Sign in with
Sign up | Sign in
Your question

parabolic antenna and beam width

Last response: in Wireless Networking
Share
Anonymous
a b F Wireless
November 25, 2004 7:42:21 PM

Archived from groups: alt.internet.wireless (More info?)

Hi all,
I purchased two LinkSys WRT54GS wifi routers to set up a wireless bridge
between two houses, the distance is about 340 meters, there are some oak
trees in the line of sight.

I am considering to buy two parabolic antennas from Stella Doradus, but
I am not sure how much gain I need to setup a stable wifi bridge:
<http://www.stelladoradus.com/2.4para.shtml&gt;

I noticed that the antennas with higher gain have smaller beam width, so
I think it is harder to 'point' them in the right direction and they are
less proof to movements (wind, etc.). Is that correct?

I am considering to get the 24 SD19 one, with 19 dBi gain, will it be
enough for my needs?

If I get an antenna with higher gain, just to be on the safe side, will
I have problems to 'point' it in the right direction or will the radio
signal be too 'strong'?
Please excuse my ignorance about this subject ...

What low loss cable do you recommend? Is the LMR400 a good one?

I think the Linksys wifi router has a RP-TNC connection, but I am not
sure about the Stella Doradus antenna, any idea?

Where can I buy a couple of short cables (e.g. 30 cm) already with the
right connectors installed at the ends?

Thanks a lot.
Anonymous
a b F Wireless
November 25, 2004 7:42:22 PM

Archived from groups: alt.internet.wireless (More info?)

I dont think you can use the wrt54gs as a bridge, it is an Access
point and wont talk to another AP.
You need something like the WAP54g that can function as a bridge, AP,
AP client or repeater.



"meATprivacyDOTnet" <me@privacy.net> wrote in message
news:30mcquF318d9pU1@uni-berlin.de...
> Hi all,
> I purchased two LinkSys WRT54GS wifi routers to set up a wireless
bridge
> between two houses, the distance is about 340 meters, there are some
oak
> trees in the line of sight.
>
> I am considering to buy two parabolic antennas from Stella Doradus,
but
> I am not sure how much gain I need to setup a stable wifi bridge:
> <http://www.stelladoradus.com/2.4para.shtml&gt;
>
> I noticed that the antennas with higher gain have smaller beam
width, so
> I think it is harder to 'point' them in the right direction and they
are
> less proof to movements (wind, etc.). Is that correct?
>
> I am considering to get the 24 SD19 one, with 19 dBi gain, will it
be
> enough for my needs?
>
> If I get an antenna with higher gain, just to be on the safe side,
will
> I have problems to 'point' it in the right direction or will the
radio
> signal be too 'strong'?
> Please excuse my ignorance about this subject ...
>
> What low loss cable do you recommend? Is the LMR400 a good one?
>
> I think the Linksys wifi router has a RP-TNC connection, but I am
not
> sure about the Stella Doradus antenna, any idea?
>
> Where can I buy a couple of short cables (e.g. 30 cm) already with
the
> right connectors installed at the ends?
>
> Thanks a lot.
Anonymous
a b F Wireless
November 25, 2004 7:42:22 PM

Archived from groups: alt.internet.wireless (More info?)

On Thu, 25 Nov 2004 16:42:21 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>I purchased two LinkSys WRT54GS wifi routers to set up a wireless bridge
>between two houses,

Send them back and get either a pair of WAP54G bridge radios, or a
single WAP54G to talk to your WRT54GS. Wireless routers don't talk to
each other (unless you're planning to use WDS).

>the distance is about 340 meters, there are some oak
>trees in the line of sight.

Trees are evil.

>I am considering to buy two parabolic antennas from Stella Doradus, but
>I am not sure how much gain I need to setup a stable wifi bridge:
><http://www.stelladoradus.com/2.4para.shtml&gt;
>
>I noticed that the antennas with higher gain have smaller beam width, so
>I think it is harder to 'point' them in the right direction and they are
>less proof to movements (wind, etc.). Is that correct?
>
>I am considering to get the 24 SD19 one, with 19 dBi gain, will it be
>enough for my needs?

Well, I'll be happy to do the math for you, as I've done several times
in this newgroup. However, I need to know coax cable type and length,
and type and length of optional pigtail. See:
http://www.ydi.com/calculation/som.php
for the basic calcs. See:

http://www.google.com/groups?selm=5m54q0dmt6cmvvb496p92...
for an example of how I grind the numbers.

>If I get an antenna with higher gain, just to be on the safe side, will
>I have problems to 'point' it in the right direction or will the radio
>signal be too 'strong'?

No. There's no such thing as too strong in such a system. The signal
level required to overload the receiver front end is fairly
substantial. I can calculate that if you'd like, but I don't think it
will be an issue at 340 meters.

>What low loss cable do you recommend? Is the LMR400 a good one?

LMR400 is a good choice. However, if the cable run is rediculously
long, heavier cable such as LMR600 may be necessary. By the time you
get to fat cable, methinks it's best to simply mount the radio on the
roof near the antenna.
http://www.sveasoft.com/articles/armored/
(About 6 page. See tiny "next" in lower right corner of page).

>I think the Linksys wifi router has a RP-TNC connection, but I am not
>sure about the Stella Doradus antenna, any idea?

WRT54GS uses R-TNC. The data sheets on the dish at:
http://www.stelladoradus.com/2.4.ghz.parabolic.antennas...
show a male N connector.

>Where can I buy a couple of short cables (e.g. 30 cm) already with the
>right connectors installed at the ends?

That would depend on what country you were located. In the US, I buy
from:
http://www.fab-corp.com
No experience with international vendors.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Related resources
Anonymous
a b F Wireless
November 26, 2004 1:23:41 AM

Archived from groups: alt.internet.wireless (More info?)

Yes, the gain of antenna comes from squashing the radiated energy into a
smaller beam, so
higher gains go hand in and with smaller beamwidths, and the beamwidth to
the -3dB points
will be approx (1.2 * wavelength / dish diameter) radians (where 2 * 3.142
radians equals 180 degrees).

Link bandwidth will drop with signal strength.
Signal strength will drop with increasing distance - 1/r^2 as the beam
spreads out, and 1/r due to attenuation through
the atmosphere - I've seen a theoretical model somewhere on the net (I can't
find it now); the 1/r term is significant at 2.4GHz as this corresponds to
water absorption.

I'm not sure what attenuation you will get in your environment, but you
could try plotting a graph of signal level against range or log(range), and
extrapolating from that.

I can't comment on the cable - but I'd keep it as short as possible to
minise losses.
Maplin (UK) do various connectors, including TNC (not connected to cable):-

http://www.maplin.co.uk/family.aspx?menu=227&menuname=R...


At a range of about 4 metres I'm getting a signal strength of -34dBm, giving
a
link rate of 54Mbd.I still get a link rate of 54Mbd even if I drop the
received signal
to -55to -60dBm (by badly positioning the antenna - down the back of a
radiator)

At a range of about 50 metres through 2 brick walls and a silver birch I get
around -70dBm,which my Linksys thinks it can manage 1Mbd through.

hope this helps.
Colin


"meATprivacyDOTnet" <me@privacy.net> wrote in message
news:30mcquF318d9pU1@uni-berlin.de...
> Hi all,
> I purchased two LinkSys WRT54GS wifi routers to set up a wireless bridge
> between two houses, the distance is about 340 meters, there are some oak
> trees in the line of sight.
>
> I am considering to buy two parabolic antennas from Stella Doradus, but I
> am not sure how much gain I need to setup a stable wifi bridge:
> <http://www.stelladoradus.com/2.4para.shtml&gt;
>
> I noticed that the antennas with higher gain have smaller beam width, so I
> think it is harder to 'point' them in the right direction and they are
> less proof to movements (wind, etc.). Is that correct?
>
> I am considering to get the 24 SD19 one, with 19 dBi gain, will it be
> enough for my needs?
>
> If I get an antenna with higher gain, just to be on the safe side, will I
> have problems to 'point' it in the right direction or will the radio
> signal be too 'strong'?
> Please excuse my ignorance about this subject ...
>
> What low loss cable do you recommend? Is the LMR400 a good one?
>
> I think the Linksys wifi router has a RP-TNC connection, but I am not sure
> about the Stella Doradus antenna, any idea?
>
> Where can I buy a couple of short cables (e.g. 30 cm) already with the
> right connectors installed at the ends?
>
> Thanks a lot.
Anonymous
a b F Wireless
November 26, 2004 1:23:42 AM

Archived from groups: alt.internet.wireless (More info?)

On Thu, 25 Nov 2004 22:23:41 -0000, "nospam" <me@privacy.net> wrote:

>Yes, the gain of antenna comes from squashing the radiated energy into a
>smaller beam, so
>higher gains go hand in and with smaller beamwidths, and the beamwidth to
>the -3dB points
>will be approx (1.2 * wavelength / dish diameter) radians (where 2 * 3.142
>radians equals 180 degrees).

Let's see how close we get with the antenna in question:
http://www.stelladoradus.com/pdfs/2.4/parabolic/grid/24...
It's interesting that the chart at:
http://www.stelladoradus.com/2.4.ghz.parabolic.antennas...
claims 10 degress for the SD27, while the data sheet says 8 degrees.

wavelength = 3x10^8 meters/sec / 2400x10^6 Hz = 0.125 meters
Dish diameter = 91 cmd
1.2 * 0.125 / 0.91 = 0.164 radians
0.164 radians * 180 / Pi = 9.4 degrees.
Yep, it works.

Argh. I'm late. More later...

>Link bandwidth will drop with signal strength.
>Signal strength will drop with increasing distance - 1/r^2 as the beam
>spreads out, and 1/r due to attenuation through
>the atmosphere - I've seen a theoretical model somewhere on the net (I can't
>find it now); the 1/r term is significant at 2.4GHz as this corresponds to
>water absorption.
>
>I'm not sure what attenuation you will get in your environment, but you
>could try plotting a graph of signal level against range or log(range), and
>extrapolating from that.
>
>I can't comment on the cable - but I'd keep it as short as possible to
>minise losses.
>Maplin (UK) do various connectors, including TNC (not connected to cable):-
>
>http://www.maplin.co.uk/family.aspx?menu=227&menuname=R...
>
>
>At a range of about 4 metres I'm getting a signal strength of -34dBm, giving
>a
> link rate of 54Mbd.I still get a link rate of 54Mbd even if I drop the
>received signal
>to -55to -60dBm (by badly positioning the antenna - down the back of a
>radiator)
>
>At a range of about 50 metres through 2 brick walls and a silver birch I get
>around -70dBm,which my Linksys thinks it can manage 1Mbd through.
>
>hope this helps.
>Colin
>
>
>"meATprivacyDOTnet" <me@privacy.net> wrote in message
>news:30mcquF318d9pU1@uni-berlin.de...
>> Hi all,
>> I purchased two LinkSys WRT54GS wifi routers to set up a wireless bridge
>> between two houses, the distance is about 340 meters, there are some oak
>> trees in the line of sight.
>>
>> I am considering to buy two parabolic antennas from Stella Doradus, but I
>> am not sure how much gain I need to setup a stable wifi bridge:
>> <http://www.stelladoradus.com/2.4para.shtml&gt;
>>
>> I noticed that the antennas with higher gain have smaller beam width, so I
>> think it is harder to 'point' them in the right direction and they are
>> less proof to movements (wind, etc.). Is that correct?
>>
>> I am considering to get the 24 SD19 one, with 19 dBi gain, will it be
>> enough for my needs?
>>
>> If I get an antenna with higher gain, just to be on the safe side, will I
>> have problems to 'point' it in the right direction or will the radio
>> signal be too 'strong'?
>> Please excuse my ignorance about this subject ...
>>
>> What low loss cable do you recommend? Is the LMR400 a good one?
>>
>> I think the Linksys wifi router has a RP-TNC connection, but I am not sure
>> about the Stella Doradus antenna, any idea?
>>
>> Where can I buy a couple of short cables (e.g. 30 cm) already with the
>> right connectors installed at the ends?
>>
>> Thanks a lot.
>

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
November 27, 2004 6:51:11 PM

Archived from groups: alt.internet.wireless (More info?)

On 11/25/04 5:31 PM, Airhead wrote:
> I dont think you can use the wrt54gs as a bridge, it is an Access
> point and wont talk to another AP.
> You need something like the WAP54g that can function as a bridge, AP,
> AP client or repeater.

Hi,
I am going to use an alternative firmware to get the bridging
functionality for the LinkSys WRT54GS router.

Check this out:
<http://www.sveasoft.com/&gt;

BTW, does anyone know any another (possibly free) alternative firmware
with bridging functionality for that router?

Thanks.
Anonymous
a b F Wireless
November 27, 2004 8:13:50 PM

Archived from groups: alt.internet.wireless (More info?)

On 11/25/04 10:12 PM, Jeff Liebermann wrote:

> Send them back and get either a pair of WAP54G bridge radios, or a
> single WAP54G to talk to your WRT54GS. Wireless routers don't talk to
> each other (unless you're planning to use WDS).

Actually I am planning to use an alternative firmware (e.g.
<http://www.sveasoft.com/&gt;) to get the bridging feature.

Can I use WDS instead? I don't think so, since I only need to do a
dedicated wifi bridge between the two LinkSys WRT54GS routers. Is that
correct?

> Trees are evil.

Yes, I know that, but they are not a lot. Will higher gain antennas help
with them?

> Well, I'll be happy to do the math for you, as I've done several times
> in this newgroup. However, I need to know coax cable type and length,
> and type and length of optional pigtail. See:
> http://www.ydi.com/calculation/som.php

I found some pigtails in my country (Italy): the length is 30 cm, the
cable type is RG-316. Is it a good one?

> No. There's no such thing as too strong in such a system. The signal
> level required to overload the receiver front end is fairly
> substantial. I can calculate that if you'd like, but I don't think it
> will be an issue at 340 meters.

Great, then I'll get the parabolic antennas with the higher gain I can
find, just to be on the safe side. I should be able to configure the
radio signal power on the LinkSys WRT54GS router.

> LMR400 is a good choice. However, if the cable run is rediculously
> long, heavier cable such as LMR600 may be necessary. By the time you
> get to fat cable, methinks it's best to simply mount the radio on the
> roof near the antenna.
> http://www.sveasoft.com/articles/armored/
> (About 6 page. See tiny "next" in lower right corner of page).

Great article, I think I'll do that, so I only need two pigtails
(probably 30 cm or so), it looks like there are no LMR400 pigtails
around, is it hard to make a pigtail out of that cable type?

> That would depend on what country you were located. In the US, I buy
> from:
> http://www.fab-corp.com

That looks a great online shop, but shipping fees are pretty high.
I found this one at a good price:
<http://cgi.ebay.it/ws/eBayISAPI.dll?ViewItem&item=57336...;
Does it look good to you?

Thanks a lot.
Anonymous
a b F Wireless
November 27, 2004 8:13:51 PM

Archived from groups: alt.internet.wireless (More info?)

"meATprivacyDOTnet" <me@privacy.net> wrote in message
news:30rne0F33142iU1@uni-berlin.de...
| On 11/25/04 10:12 PM, Jeff Liebermann wrote:
|
| > Send them back and get either a pair of WAP54G bridge radios, or a
| > single WAP54G to talk to your WRT54GS. Wireless routers don't talk to
| > each other (unless you're planning to use WDS).
|
| Actually I am planning to use an alternative firmware (e.g.
| <http://www.sveasoft.com/&gt;) to get the bridging feature.
|
| Can I use WDS instead? I don't think so, since I only need to do a
| dedicated wifi bridge between the two LinkSys WRT54GS routers. Is that
| correct?
|
| > Trees are evil.
|
| Yes, I know that, but they are not a lot. Will higher gain antennas help
| with them?
|

To an extent yes but the link budget (path loss) is hard to estimate.
Signal levels can vary by season, if the leaves have dew (ie wet/dry)

| > Well, I'll be happy to do the math for you, as I've done several times
| > in this newgroup. However, I need to know coax cable type and length,
| > and type and length of optional pigtail. See:
| > http://www.ydi.com/calculation/som.php
|
| I found some pigtails in my country (Italy): the length is 30 cm, the
| cable type is RG-316. Is it a good one?

Don;t know much about the RG-316 but I do know that with any coax the
quality can vary considerably.
|
Anonymous
a b F Wireless
November 27, 2004 8:13:51 PM

Archived from groups: alt.internet.wireless (More info?)

On Sat, 27 Nov 2004 17:13:50 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>Actually I am planning to use an alternative firmware (e.g.
><http://www.sveasoft.com/&gt;) to get the bridging feature.

OK. I don't know much about the various alternative firmwares.

>Can I use WDS instead?

To do what? The only description of what you intended to accomplish
is to "bridge" between the two houses.

>I don't think so, since I only need to do a
>dedicated wifi bridge between the two LinkSys WRT54GS routers. Is that
>correct?

Again, to do what? Are you going to have wireless clients running
around each end, that need to access the internet through the bridge
radios? Will there be wired clients on both ends? Can you tolerate
the 50% reduction in thruput caused by WDS?

>Yes, I know that, but they are not a lot. Will higher gain antennas help
>with them?

Sure, higher gain antennas will help drill through folliage. However,
if the signal is completely blocked by the trees, even the largest
antennas will result in an unsable connection.

>I found some pigtails in my country (Italy): the length is 30 cm, the
>cable type is RG-316. Is it a good one?

No. The outer diameter is 0.098". This very small coax is made for
connecting between circuit boards and external panel mount connectors.
Loss is 0.60dB/ft. At 30cm (about 10") it's not going to make much
difference. However, the pigtail I'm referring to is the one between
your WRT54G and the LMR-400 coax cable from the rooftop antenna. With
coax that small, one mistake and you're gonna rip the coax out of the
connectors. I suggest pigtails from something stronger like LMR-100A
which is 0.150" dia (and 0.35dB/ft).

>> No. There's no such thing as too strong in such a system. The signal
>> level required to overload the receiver front end is fairly
>> substantial. I can calculate that if you'd like, but I don't think it
>> will be an issue at 340 meters.

>Great, then I'll get the parabolic antennas with the higher gain I can
>find, just to be on the safe side. I should be able to configure the
>radio signal power on the LinkSys WRT54GS router.

Yes, but you'll probably want and need the strongest signal possible.
The connection speed is totally dependent on the signal strength (and
s/n ratio). If you loose signal strength, the error rate will
increase, which causes the bridge radios to drop their data rate to
reduce errrors.

>> http://www.sveasoft.com/articles/armored/
>> (About 6 page. See tiny "next" in lower right corner of page).

>Great article, I think I'll do that, so I only need two pigtails
>(probably 30 cm or so), it looks like there are no LMR400 pigtails
>around, is it hard to make a pigtail out of that cable type?

The reason you need a pigtail is that LMR-400 is very stiff. It will
literally tear apart a connector or drag the WRT54G across the table.
You need a short piece of something between the LMR-400 and the radio
to allow some movement if necessary. You can get an R-TNC connector
on the end of a piece of LMR-400 coax. You can also get an N to R-TNC
adapter. However, both tof these methods, which do not require a
pigtail, will cause problems with connector alignment, damage, and
moving boxes.

It's not difficult to crimp your own connectors. RF-Industries makes
most of the connectors. About $5-$8/ea from Digikey. The crimping
tools are available for about $35.
http://www.hyperlinktech.com/web/cable_tools.php
Plan on ruining a few while learning to use the crimpers. Also, be
sure to get the cable stripper. I do mine by hand, with a pocket
knife, but I'll admit that the stripper does a better job.

>I found this one at a good price:
><http://cgi.ebay.it/ws/eBayISAPI.dll?ViewItem&item=57336...;
>Does it look good to you?

For $12, it's a bargain. That's less than what the connectors usually
cost me. The LMR-195 is much more flexible than LMR-100A but somewhat
more attenuation (0.55dB/ft).

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
November 27, 2004 8:25:55 PM

Archived from groups: alt.internet.wireless (More info?)

On 11/25/04 11:57 PM, Jeff Liebermann wrote:

> Let's see how close we get with the antenna in question:
> http://www.stelladoradus.com/pdfs/2.4/parabolic/grid/24...
> It's interesting that the chart at:
> http://www.stelladoradus.com/2.4.ghz.parabolic.antennas...
> claims 10 degress for the SD27, while the data sheet says 8 degrees.
>
> wavelength = 3x10^8 meters/sec / 2400x10^6 Hz = 0.125 meters
> Dish diameter = 91 cmd
> 1.2 * 0.125 / 0.91 = 0.164 radians
> 0.164 radians * 180 / Pi = 9.4 degrees.
> Yep, it works.
>
> Argh. I'm late. More later...

So will this be a good antenna for a 350 meters link?

Don't forget a couple of trees in the LOS ...

Thanks.
Anonymous
a b F Wireless
November 27, 2004 8:25:56 PM

Archived from groups: alt.internet.wireless (More info?)

On Sat, 27 Nov 2004 17:25:55 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>On 11/25/04 11:57 PM, Jeff Liebermann wrote:
>
>> Let's see how close we get with the antenna in question:
>> http://www.stelladoradus.com/pdfs/2.4/parabolic/grid/24...
>> It's interesting that the chart at:
>> http://www.stelladoradus.com/2.4.ghz.parabolic.antennas...
>> claims 10 degress for the SD27, while the data sheet says 8 degrees.
>>
>> wavelength = 3x10^8 meters/sec / 2400x10^6 Hz = 0.125 meters
>> Dish diameter = 91 cmd
>> 1.2 * 0.125 / 0.91 = 0.164 radians
>> 0.164 radians * 180 / Pi = 9.4 degrees.
>> Yep, it works.
>>
>> Argh. I'm late. More later...

>So will this be a good antenna for a 350 meters link?

Probably. My seat of the pants guess is that 24dBi on both ends is
probably needed to drill through two trees. However I'm a
practitioner of the black art of calculation and always grind the
numbers before passing judgement. You haven't supplied a few key
pieces of missing information, so I can't grind any numbers.

From a previous posting:

Well, I'll be happy to do the math for you, as I've done several
times in this newgroup. However, I need to know coax cable type
and length, and type and length of optional pigtail. See:
http://www.ydi.com/calculation/som.php
for the basic calcs. See:

http://www.google.com/groups?selm=5m54q0dmt6cmvvb496p92...
for an example of how I grind the numbers.

>Don't forget a couple of trees in the LOS ...

Don't forget the cable lengths (each end). I can usually give a good
guess as to the penetration through trees based on some foliage
attenuation models and personal experience. For that, I need a photo
with the fresnel zone marked on the image, as well as a photo of the
cross section of the intended path. As a general rule of thumb, if
you have soaking wet or frozen broadleaf trees, nothing will work. If
it's needles or very dry (desert) shrubbage, it can be penetrated.
Absolutely nothing goes through a trunk.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
November 28, 2004 9:25:17 PM

Archived from groups: alt.internet.wireless (More info?)

On 11/28/04 12:44 AM, Jeff Liebermann wrote:

> Again, to do what? Are you going to have wireless clients running
> around each end, that need to access the internet through the bridge
> radios? Will there be wired clients on both ends? Can you tolerate
> the 50% reduction in thruput caused by WDS?

Let me explain better.

I would like to use the LinkSys boxes to setup the wifi bridge between
the two buildings.

Then I'll attach (wired, not via radio) the computers of each building
to the LAN ports of each WRT54GS or to a network switch connected
(wired) to the WRT54GS.

So, no wireless clients will be connected to the WRT54GS boxes (except
for themselves).

I want the computers of both building to be on the same network (e.g.
192.168.0.1/255.255.255.0).

I also want to share the broadband connection: one of the building has a
high speed connection to the Internet using a Cisco router.

What is the best way to realize such wifi bridge?

Set one WRT54GS in AP mode and the other one in client mode?

This should be possible with the Sveasoft Satori (public) firmware, but
it looks like there are a couple of problems with that:
- You have to disable lookback interface on the client WRT54GS, not sure
why and if it causes any problem.
- Only one (wired) client can be connected to the client WRT54GS,
otherwise things won't work well: this is a big limitation for me.

Can anyone confirm this?

It looks like the Sveasoft Alchemy (pre-release) firmware handles the
bridge feature in a different way, but the firmware is not public yet
and I cannot test it ...

That's why I thought to give WDS a try.

Here is the WDS definition:

<http://www.broadbandbuyer.co.uk/BuyersGuide/FAQDetail.a...;
---
WDS (Wireless Distribution System) is a Wireless Access Point mode that
enables wireless bridging in which WDS APs communicate only with each
other only (without allowing for wireless clients or stations to access
them), and/or wireless repeating in which APs communicate both with each
other and with wireless stations (at the expense of half the throughput).
---

It looks like it may be a good way to get a wireless bridge between two
WRT54GS boxes and have the full bandwidth available, since I am not
going to connect any wireless client to the LinkSys boxes.

Do you think that will work?

> Sure, higher gain antennas will help drill through folliage. However,
> if the signal is completely blocked by the trees, even the largest
> antennas will result in an unsable connection.

I can see a little bit through the foliage, hopefully eve the radio
signal will be able to pass through ...

> No. The outer diameter is 0.098". This very small coax is made for
> connecting between circuit boards and external panel mount connectors.
> Loss is 0.60dB/ft. At 30cm (about 10") it's not going to make much
> difference. However, the pigtail I'm referring to is the one between
> your WRT54G and the LMR-400 coax cable from the rooftop antenna. With
> coax that small, one mistake and you're gonna rip the coax out of the
> connectors. I suggest pigtails from something stronger like LMR-100A
> which is 0.150" dia (and 0.35dB/ft).

I'll be putting each WRT54GS device in an almost sealed box next to the
antenna, all I need is pigtail between the device and the antenna, no
need for the LMR-400 coax cable.

> The reason you need a pigtail is that LMR-400 is very stiff. It will
> literally tear apart a connector or drag the WRT54G across the table.
> You need a short piece of something between the LMR-400 and the radio
> to allow some movement if necessary. You can get an R-TNC connector
> on the end of a piece of LMR-400 coax. You can also get an N to R-TNC
> adapter. However, both tof these methods, which do not require a
> pigtail, will cause problems with connector alignment, damage, and
> moving boxes.
>
> It's not difficult to crimp your own connectors. RF-Industries makes
> most of the connectors. About $5-$8/ea from Digikey. The crimping
> tools are available for about $35.
> http://www.hyperlinktech.com/web/cable_tools.php
> Plan on ruining a few while learning to use the crimpers. Also, be
> sure to get the cable stripper. I do mine by hand, with a pocket
> knife, but I'll admit that the stripper does a better job.

Thanks for the great explanation, I haven't seen a LMR-400 coax cable
yet, I had no idea it was so stiff ...

> For $12, it's a bargain. That's less than what the connectors usually
> cost me. The LMR-195 is much more flexible than LMR-100A but somewhat
> more attenuation (0.55dB/ft).

Actually it looks like the opposite is true: the LMR-100A is thinner and
has more attenuation than the LMR-195:
<http://www.mtwirefree.net/w3eme/coax.htm&gt;
<http://www.timesmicrowave.com/cgi-bin/calculate.pl&gt;

Unless I am missing something, the eBay pigtail seems very good, I think
I am going to get a couple of them.

Thanks.
Anonymous
a b F Wireless
November 28, 2004 9:28:16 PM

Archived from groups: alt.internet.wireless (More info?)

On 11/28/04 12:14 AM, Jeff Liebermann wrote:

> Don't forget the cable lengths (each end). I can usually give a good
> guess as to the penetration through trees based on some foliage
> attenuation models and personal experience. For that, I need a photo
> with the fresnel zone marked on the image, as well as a photo of the
> cross section of the intended path. As a general rule of thumb, if
> you have soaking wet or frozen broadleaf trees, nothing will work. If
> it's needles or very dry (desert) shrubbage, it can be penetrated.

Except for the pigtail, there will be no cable at each installation,
since I'll put the LinkSys box next to the antenna.

What would be the best way to get you some pics?

Thanks a lot for your advise.
Anonymous
a b F Wireless
November 28, 2004 9:28:17 PM

Archived from groups: alt.internet.wireless (More info?)

On Sun, 28 Nov 2004 18:28:16 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>Except for the pigtail, there will be no cable at each installation,
>since I'll put the LinkSys box next to the antenna.

OK, I can work with that and a bit of guesswork.

>What would be the best way to get you some pics?

Email. Addresses in signature are real. Don't send Bcc: or I'll have
to fish it out of the spam trap.



--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
November 28, 2004 10:16:15 PM

Archived from groups: alt.internet.wireless (More info?)

On Sun, 28 Nov 2004 18:28:16 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>Except for the pigtail, there will be no cable at each installation,
>since I'll put the LinkSys box next to the antenna.

Ok. Let's run the initial numbers. I'll throw in the trees when I
see them. See:
http://www.ydi.com/calculation/som.php
What you're looking for is an absolute minimum of 10dB fade margin.
The system will work with 0dB of fade margin, but not be particularly
stable. A passing bird would cause the signal to disappear. At 10dB,
if set to 802.11g only (ignore 802.11b), will probably be running at
12Mbps connection speed (and about half that in thruput). Any
interference will make it worse.

I use these number for receiver sensitivity at various connection
speeds. They're from a D-Link DI-624 data sheet and appear to be
rather typical. You're WRT54GS will be close.
* 54Mbps OFDM, 10% PER, -68dBm)
* 48Mbps OFDM, 10% PER, -68dBm)
* 36Mbps OFDM, 10% PER, -75dBm)
* 24Mbps OFDM, 10% PER, -79dBm)
* 18Mbps OFDM, 10% PER, -82dBm)
* 12Mbps OFDM, 10% PER, -84dBm)
* 11Mbps CCK, 8% PER, -82dBm)
* 9Mbps OFDM, 10% PER, -87dBm)
* 6Mbps OFDM, 10% PER, -88dBm)
* 5.5Mbps CCK, 8% PER, -85dBm)
* 2Mbps QPSK, 8% PER, -86dBm)
* 1Mbps BPSK, 8% PER, -89dBm)

Using my crystal ball and some guesswork:
Distance = 0.211 miles (340 meters)
TX power = +15dBm
RX sens = -84dBm (at 12Mbits/sec OFDM)
TX ant gain = 17dBi (medium size dish)
RX ant gain = 17dBi (same at other end)
TX coax loss = -3dB (1ft LMR-195 plus a mess of connectors)
RX coax loss = -3dB (same at other end)
which yields a fade margin of 36dB which is quite good. That would
give you a max possible 26dB for foliage loss, which is reasonable for
a small broadleaf not very dense tree. A really bad approximation is
about 1dB per meter attenuation through the "typical" tree (whatever
that means) minus the trunk, heavy branches, and water logged leaves
(banana, tropical, etc). If you increase the antenna gain to 24dBi,
your fade margin will be 50dB, leaving 40dB for foliage loss. That's
enough to go through most "typical" trees.

This should give you some clues on trees:
http://www.wlanantennas.com/wlan_faq_radioprop.htm

Yeah, methinks it will work at 340 meters with 17dBi dishes.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
November 29, 2004 2:33:37 PM

Archived from groups: alt.internet.wireless (More info?)

On 11/29/04 1:58 AM, Jeff Liebermann wrote:

> To the best of my knowledge (i.e. I might be wrong), the stock WRT54GS
> (Linksys firmware) does not have a client mode. The WAP54G certainly
> does. Looks like Sveasoft Satori 4.0 does:
> http://www.linksysinfo.org/modules.php?name=News&file=a...
> The problem with this derrangement is that it will bridge exactly one
> MAC address. That's fine if your remote site only has one computah,
> but that's never the case. You can do it by enabling the VPN
> termination on your unspecified Cisco router and gettting a VPN router
> at the other end. Messy, but possible. Not recommended.

I have multiple computers at the remote site, so the single MAC address
will be an issue for me.
I got the WRT54GS instead of the WAP54G because it has better hardware
(fast CPU, more memory, SpeedBoster, etc.) and I thought the alternative
firmware would add all the WAP54G features ...

> Yes, WDS will work. See:
> http://www.orinocowireless.com/support/techbulletins/TB...
> for one of the better writeups on WDS. Go down to "Performance
> Evaluations" and try to predict what you'll get. Since Orinoco used
> 802.11b, your numbers will be about 4 times better if you have lots of
> signal to play with. Note that item #3 on Page 10, where both clients
> are wired to the access points with a single radio in each access
> point, yields the worst thruput. Yeah, it will work if you don't mind
> running at the speed of a snail.

It looks like there is an error on page 10, item #3 should read "Both
clients WIRELESSLY connected to each AP ..." instead of "Both clients
WIRED connected to each AP ...", at least according to the diagram on
page 11.

My setup would be like item #1 ("Both clients wired connected to each
AP"), that yiedls the best throughput.
I think that's close to the actual maximum 802.11b throughput: it looks
like you don't loose any bandwidth using WDS to setup a wireless bridge
between two APs and using wired clients.

> You're probably safe with LMR-100 or LMR-195. I would not go with the
> really tiny stuff.

Why most people use LMR-100A instead of LMR-195 (less loss) for pigtails?

> Reminder: Think about where the water will go if it gets inside or
> drips down the coax. It most assuredly will.

Will drilling a hole in the bottom of the sealed box help?

> Incidentally, you may find these handy as most commercial antennas use
> N pigtails. An N to R-TNC adapter would eliminate the added pigtail.
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5734...

That looks great.
What would be the approximate signal loss of such adapter?

If it is lower than an additional pigtail, as I think, why people keep
using the pigtail?

BTW, does anyone sell high gain parabolic antennas with a RP-TNC
connector, instead of the common N type connector?

Thanks a lot.
Anonymous
a b F Wireless
November 29, 2004 2:33:38 PM

Archived from groups: alt.internet.wireless (More info?)

On Mon, 29 Nov 2004 11:33:37 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>> Yes, WDS will work. See:
>> http://www.orinocowireless.com/support/techbulletins/TB...

>It looks like there is an error on page 10, item #3 should read "Both
>clients WIRELESSLY connected to each AP ..." instead of "Both clients
>WIRED connected to each AP ...", at least according to the diagram on
>page 11.

Egads, your correct. My appologies. I've never tried to use WDS to
replace a transparent bridge and have no clue what might happen. My
sense of smell tells me that something is wrong, because if it did
work, then everyone would be using it to replace "workgroup bridges"
and "game adapters" to connect multiple devices. The key part of a
transparent bridge is that the boxes have a (proprietary) bridging
protocol, that distributes the MAC address to "port number" table to
BOTH ends of the bridge to keep traffic down to a minimum. Without
this protocol, the bridges will be sending a substantial amount of
traffic that goes nowhere. I'm not sure if WDS can do that.

>My setup would be like item #1 ("Both clients wired connected to each
>AP"), that yiedls the best throughput.
>I think that's close to the actual maximum 802.11b throughput: it looks
>like you don't loose any bandwidth using WDS to setup a wireless bridge
>between two APs and using wired clients.

I think the problem isn't the bandwidth through the bridge. It's what
the bridge decides about traffic that should go across the bridge. In
a transparent bridge, if Radio #1 doesn't have a list of MAC addresses
of devices that are accross the bridge, it might send everything (as
in a hub). I'm not sure how it works and might be wrong, but it's
worth testing. I don't have a single box in the office that does WDS
so I can't setup a test for at least a few days.

>Why most people use LMR-100A instead of LMR-195 (less loss) for pigtails?

I don't know. All of the commerically made R-TNC to N pigtails I have
are LMR-100. It's quite stiff and I guess if I could have bought
LMR-195, I would have ordered it. For short lengths, the difference
in loss is negligible. I guess it's "traditional"?

>> Reminder: Think about where the water will go if it gets inside or
>> drips down the coax. It most assuredly will.

>Will drilling a hole in the bottom of the sealed box help?

Yes. I posted a rant on the subject or waterproofing in this
newsgroup in the past. Basically, the only form of sealed
waterproofing that really works is a pressurized box. If there's a
path to the atmosphere, water will condense inside. I do use
pressurized boxes and coax runs for commercial towers, but that's
overkill home use, where access is fairly trivial. I also conformal
coat the boards, which is also overkill (and messy). Two small holes
in the bottom of the box will be sufficient to drain off anything that
accumulates. The heat from the board will be sufficient to prevent
condensation on the board, but not on all the other hardware which
will tend to corrode. Use stainless as much as possible.

>> Incidentally, you may find these handy as most commercial antennas use
>> N pigtails. An N to R-TNC adapter would eliminate the added pigtail.
>> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5734...

>That looks great.
>What would be the approximate signal loss of such adapter?

I could look it up, but my guess is 1dB. I use a rule of thumb of
0.5dB per connector pair and 1dB for adapters. (That's about 10%
power loss for the adapter). It's probably made by RF Industries.
Download the catalog (9MBtyes)
http://www.rfcoaxconnectors.com
and see if you can find a PT-4000-135 (R-TNC male to N female).

Hmmm... I notice that they offer pigtails in LMR-195.

>If it is lower than an additional pigtail, as I think, why people keep
>using the pigtail?

Did you read my previous explanation? The problem is that LMR-400 is
usually used for runs between the access point and the antenna. No
pigtail required at the antenna, but if you installed an R-TNC
connector on the LMR-400, the stiff coax would lift the radio off the
table or otherwise be a mechanical problem. In extreme cases, it
could rip the connector out of the radio (as on a PCMCIA card). You
could possibly get away with it using a R-TNC connector, but an SMA
connector on the end of an LMR-400 coax cable will surely break off.

>BTW, does anyone sell high gain parabolic antennas with a RP-TNC
>connector, instead of the common N type connector?

I don't think so and I have a guess as to why. The problem is that
most of the antenna manufacturers cut costs by using the absolute
cheapest coax possible for their pigtails. RG-8/u and RG-58a/u are
common. The reason they can get away with that is the difference in
loss between quality and junk coax over a 1ft distance is
insignificant. Anything will work. I don't think anyone makes an
R-TNC crimp connector for RG-8/u junk coax, only N connectors.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
November 29, 2004 2:38:28 PM

Archived from groups: alt.internet.wireless (More info?)

On 11/29/04 4:16 AM, Jeff Liebermann wrote:

> Yeah, methinks it will work at 340 meters with 17dBi dishes.

Thanks for the calculations: I'll try to get the 24 dBi parabolic
antennas anyway, just to be on the safe side.

I'll try to send you a couple of pics of the trees as soon as I have a
chance.

Thanks again for your very useful advice.
Anonymous
a b F Wireless
November 30, 2004 12:57:17 AM

Archived from groups: alt.internet.wireless (More info?)

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:

> I think the problem isn't the bandwidth through the bridge. It's what
> the bridge decides about traffic that should go across the bridge. In

If the bridges are each connected to switches, won't the switches make much
of that decision for them, only letting them see data for destinations seen
on that port on the switch?

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
Anonymous
a b F Wireless
November 30, 2004 5:49:59 AM

Archived from groups: alt.internet.wireless (More info?)

On Mon, 29 Nov 2004 21:57:17 +0000 (UTC),
dold@XReXXparab.usenet.us.com wrote:

>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote:
>
>> I think the problem isn't the bandwidth through the bridge. It's what
>> the bridge decides about traffic that should go across the bridge. In

>If the bridges are each connected to switches, won't the switches make much
>of that decision for them, only letting them see data for destinations seen
>on that port on the switch?

Duh... yes. I forgot that most wireless routers have built in 4 port
switches. The switches (actually multi-port bridges) will take care
of bridging function. I'm not sure how it would work with more than
two WDS routers, but that's not an issue here. I still smell
something is wrong, but my previous guess was not it. Thanks.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# jeffl@comix.santa-cruz.ca.us
# 831.421.6491 digital_pager jeffl@cruzio.com AE6KS
Anonymous
a b F Wireless
November 30, 2004 2:23:41 PM

Archived from groups: alt.internet.wireless (More info?)

On 11/29/04 6:42 PM, Jeff Liebermann wrote:

> I think the problem isn't the bandwidth through the bridge. It's what
> the bridge decides about traffic that should go across the bridge. In
> a transparent bridge, if Radio #1 doesn't have a list of MAC addresses
> of devices that are accross the bridge, it might send everything (as
> in a hub). I'm not sure how it works and might be wrong, but it's
> worth testing. I don't have a single box in the office that does WDS
> so I can't setup a test for at least a few days.

I'll give WDS a try as soon as I have a chance and post back to the
newsgroup with the results.

> I don't know. All of the commerically made R-TNC to N pigtails I have
> are LMR-100. It's quite stiff and I guess if I could have bought
> LMR-195, I would have ordered it. For short lengths, the difference
> in loss is negligible. I guess it's "traditional"?

I read a couple of messages about LMR-100A fitting better the connectors
than LMR-195, due to the cable size. Is that correct?

> I could look it up, but my guess is 1dB. I use a rule of thumb of
> 0.5dB per connector pair and 1dB for adapters. (That's about 10%
> power loss for the adapter). It's probably made by RF Industries.
> Download the catalog (9MBtyes)
> http://www.rfcoaxconnectors.com
> and see if you can find a PT-4000-135 (R-TNC male to N female).

I downloaded the catalog, but couldn't find that adapter, anyway I think
your guess is pretty good.

> Did you read my previous explanation? The problem is that LMR-400 is
> usually used for runs between the access point and the antenna. No
> pigtail required at the antenna, but if you installed an R-TNC
> connector on the LMR-400, the stiff coax would lift the radio off the
> table or otherwise be a mechanical problem. In extreme cases, it
> could rip the connector out of the radio (as on a PCMCIA card). You
> could possibly get away with it using a R-TNC connector, but an SMA
> connector on the end of an LMR-400 coax cable will surely break off.

Thanks for the further explanation, I got it now.
Since I am going to put the antenna next to the AP, I'll get the R-TNC
male to N female adapter, no additional pigtail needed for me.

> I don't think so and I have a guess as to why. The problem is that
> most of the antenna manufacturers cut costs by using the absolute
> cheapest coax possible for their pigtails. RG-8/u and RG-58a/u are
> common. The reason they can get away with that is the difference in
> loss between quality and junk coax over a 1ft distance is
> insignificant. Anything will work. I don't think anyone makes an
> R-TNC crimp connector for RG-8/u junk coax, only N connectors.

That sounds reasonable.
It looks like Stella Doradus uses RG-213/u (60 cm) cable for the antenna
pigtail:
<http://www.stelladoradus.com/2.4.ghz.parabolic.antennas...;

Is it a good one?
BTW, what does the 'u' stand for?

Thanks again.
November 30, 2004 4:42:11 PM

Archived from groups: alt.internet.wireless (More info?)

"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in message
news:cshcq0h4cbvrjkt21km3t97jshc1rkg6il@4ax.com...
>> http://www.sveasoft.com/articles/armored/
> (About 6 page. See tiny "next" in lower right corner of page).

I got chills when I saw the picture of the plate being drilled without being
clamped and just being hand held. My friend did *major* damage to his hand
doing that while using an seemingly innocent small drill press when the
workpiece caught and spun.



>
> >I think the Linksys wifi router has a RP-TNC connection, but I am not
> >sure about the Stella Doradus antenna, any idea?
>
> WRT54GS uses R-TNC. The data sheets on the dish at:
> http://www.stelladoradus.com/2.4.ghz.parabolic.antennas...
> show a male N connector.
>
> >Where can I buy a couple of short cables (e.g. 30 cm) already with the
> >right connectors installed at the ends?
>
> That would depend on what country you were located. In the US, I buy
> from:
> http://www.fab-corp.com
> No experience with international vendors.
>
>
> --
> Jeff Liebermann jeffl@comix.santa-cruz.ca.us
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
December 1, 2004 12:37:39 AM

Archived from groups: alt.internet.wireless (More info?)

George <george@nospam.invalid> wrote:
>>> http://www.sveasoft.com/articles/armored/

> I got chills when I saw the picture of the plate being drilled without being
> clamped and just being hand held. My friend did *major* damage to his hand
> doing that while using an seemingly innocent small drill press when the
> workpiece caught and spun.

And such a nice picture of the same metal plate _clamped_ to the drill
press on the previous page.

I did the opposite of your friend. A 1/2" handheld drill motor spun me
around when it caught in a heavy steel plate. No long term damage, but I
was young and invincible then.

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5
Anonymous
a b F Wireless
December 1, 2004 2:12:38 AM

Archived from groups: alt.internet.wireless (More info?)

On Tue, 30 Nov 2004 11:23:41 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>I read a couple of messages about LMR-100A fitting better the connectors
>than LMR-195, due to the cable size. Is that correct?

Well, the connectors and cable diameters for LMR-100A and LMR-195 are
completely different. Hopefully, someone didn't just mix up the crimp
connectors and crimp tools.
http://www.timesmicrowave.com/telecom/pdf/LMRGuide.pdf

>That sounds reasonable.
>It looks like Stella Doradus uses RG-213/u (60 cm) cable for the antenna
>pigtail:
><http://www.stelladoradus.com/2.4.ghz.parabolic.antennas...;
>Is it a good one?

RG-213/u is double shielded RG-8/u. For a 1ft run, it's fine.

>BTW, what does the 'u' stand for?

RG means "radio guide" as in something that guides radio waves to
whever they're going. The various numbers were originally the page
numbers of some lost military catalog of coax cables. The /A /B /U
are the different types of jackets. I think /u means
non-contaminating jacket. Like any other significant numbering
system, the military dumped the whole RG mess in about 1945 in favour
of the C17 numbering system which nobody uses.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# jeffl@comix.santa-cruz.ca.us
# 831.421.6491 digital_pager jeffl@cruzio.com AE6KS
Anonymous
a b F Wireless
December 1, 2004 2:19:51 AM

Archived from groups: alt.internet.wireless (More info?)

On Tue, 30 Nov 2004 21:37:39 +0000 (UTC),
dold@XReXXparab.usenet.us.com wrote:

>George <george@nospam.invalid> wrote:
>>>> http://www.sveasoft.com/articles/armored/
>
>> I got chills when I saw the picture of the plate being drilled without being
>> clamped and just being hand held. My friend did *major* damage to his hand
>> doing that while using an seemingly innocent small drill press when the
>> workpiece caught and spun.

>And such a nice picture of the same metal plate _clamped_ to the drill
>press on the previous page.

>I did the opposite of your friend. A 1/2" handheld drill motor spun me
>around when it caught in a heavy steel plate. No long term damage, but I
>was young and invincible then.

Bah. For a really fun time, try running a gasoline engine powered
post hole digger. If you want a fun carousel ride, you've found the
right contraption. Stick the auger into a rock and around you go.
These do have a "dead mans switch" on the handles, but I figured out
that one would be dead by the time it works.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# jeffl@comix.santa-cruz.ca.us
# 831.421.6491 digital_pager jeffl@cruzio.com AE6KS
Anonymous
a b F Wireless
December 5, 2004 9:21:51 PM

Archived from groups: alt.internet.wireless (More info?)

On 11/29/04 4:16 AM, Jeff Liebermann wrote:

> I use these number for receiver sensitivity at various connection
> speeds. They're from a D-Link DI-624 data sheet and appear to be
> rather typical. You're WRT54GS will be close.
> * 54Mbps OFDM, 10% PER, -68dBm)
> * 48Mbps OFDM, 10% PER, -68dBm)
> * 36Mbps OFDM, 10% PER, -75dBm)
> * 24Mbps OFDM, 10% PER, -79dBm)
> * 18Mbps OFDM, 10% PER, -82dBm)
> * 12Mbps OFDM, 10% PER, -84dBm)
> * 11Mbps CCK, 8% PER, -82dBm)
> * 9Mbps OFDM, 10% PER, -87dBm)
> * 6Mbps OFDM, 10% PER, -88dBm)
> * 5.5Mbps CCK, 8% PER, -85dBm)
> * 2Mbps QPSK, 8% PER, -86dBm)
> * 1Mbps BPSK, 8% PER, -89dBm)

It looks like the WRT54GS uses the BroadCom 4712 chipset:
<http://www.ecsl.cs.sunysb.edu/~jchen/wrt54gs/wrt54gs.ht...;
<http://www.broadcom.com/products/product.php?product_id...;
<http://www.broadcom.com/press/release.php?id=432998&gt;

The datasheet is at the following URL:
<http://www.broadcom.com/collateral/pb/94712-PB02-R.pdf&...;

The sensitivity looks a little better than the D-Link one:
---
-95 dBm at 1 Mbps
-87 dBm at 11 Mbps
-70 dBm at 54 Mbps
---

> Using my crystal ball and some guesswork:
> Distance = 0.211 miles (340 meters)
> TX power = +15dBm
> RX sens = -84dBm (at 12Mbits/sec OFDM)
> TX ant gain = 17dBi (medium size dish)
> RX ant gain = 17dBi (same at other end)
> TX coax loss = -3dB (1ft LMR-195 plus a mess of connectors)
> RX coax loss = -3dB (same at other end)
> which yields a fade margin of 36dB which is quite good.

I cannot get the same results as yours using the online calculator:
<http://www.ydi.com/calculation/som.php&gt;

I use the same input data and 2400 MHz as operating frequency, I get the
following results:
---
Fress Space Loss: 90.7 dB
Rx Signal Level: -35.7 dBm
Theoretical System Operating Margin: 48.3 dB
---

Any idea? Should I use a different frequency?

> That would
> give you a max possible 26dB for foliage loss, which is reasonable for
> a small broadleaf not very dense tree. A really bad approximation is
> about 1dB per meter attenuation through the "typical" tree (whatever
> that means) minus the trunk, heavy branches, and water logged leaves
> (banana, tropical, etc). If you increase the antenna gain to 24dBi,
> your fade margin will be 50dB, leaving 40dB for foliage loss. That's
> enough to go through most "typical" trees.

Also, if I run the calculations with 24 dBi (instead of 17) antennas and
1 dBm (instead of 15) Tx Power, I get the same results:
---
Fress Space Loss: 90.7 dB
Rx Signal Level: -35.7 dBm
Theoretical System Operating Margin: 48.3 dB
---

It looks like the more gain in the antennas (7 x 2 = +14 dBi) balances
perfectly the smaller Tx Power (1 - 15 = -14 dBm), is that correct?

Is the RX Signal Level (-35.7 dBm) too much?
Will it overload the LinkSys WRT54GS receiver?

I have no idea about the overload point for the Broadcom chipset.
There is no mention about it in the above datasheet.
Any guess about it?

As suggested, I should be able to simulate the effects by putting the
two LinkSys boxes next to each other with the included omnidirectional
antennas.

What would be the exact distance for simulating that signal level (-35.7
dBm) or a little stronger?

The reason for which I am considering to get the 24 dBi antennas instead
of the 17 dBi ones (that would probably work fine too) is that I would
like to get a full reliable 54 Mbps link, also consider the trees in the
LOS, they will attenuate the signal ...

Also, it looks you can set the LinkSys WRT54GS transmit power from 0 to
84 mW:
<http://docs.sveasoft.com/SV-Wireless-AdvancedSettings.h...;

What would be the equivalent numbers in dB?

If I set it to 0 mW, will it transmit the radio signal at all?

Basically I would like to run the LinkSys box at the minimum transmit
power and take adavantage of the high gain parabolic antennas.

Is it a good plan?

Thanks a lot, I am learning a lot from this ng.
Anonymous
a b F Wireless
December 5, 2004 9:21:52 PM

Archived from groups: alt.internet.wireless (More info?)

On Sun, 05 Dec 2004 18:21:51 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>It looks like the WRT54GS uses the BroadCom 4712 chipset:

Yep. Broadcom BCM4712KPB

>The datasheet is at the following URL:
><http://www.broadcom.com/collateral/pb/94712-PB02-R.pdf&...;
>
>The sensitivity looks a little better than the D-Link one:
>---
>-95 dBm at 1 Mbps
>-87 dBm at 11 Mbps
>-70 dBm at 54 Mbps

That's the sensitivity of the chip, measured at the input to the chip
and not the sensitivity measured after going through a diversity
switch IC, across some lossy G10 circuit board, through a lossy coax
cable, and into 1/2 of a lossy R-TNC pair. Use the sensitivity of the
final product, not that of the chip.

>> Using my crystal ball and some guesswork:
>> Distance = 0.211 miles (340 meters)
>> TX power = +15dBm
>> RX sens = -84dBm (at 12Mbits/sec OFDM)
>> TX ant gain = 17dBi (medium size dish)
>> RX ant gain = 17dBi (same at other end)
>> TX coax loss = -3dB (1ft LMR-195 plus a mess of connectors)
>> RX coax loss = -3dB (same at other end)
>> which yields a fade margin of 36dB which is quite good.

>I cannot get the same results as yours using the online calculator:
><http://www.ydi.com/calculation/som.php&gt;
>
>I use the same input data and 2400 MHz as operating frequency, I get the
>following results:
>---
>Fress Space Loss: 90.7 dB
>Rx Signal Level: -35.7 dBm
>Theoretical System Operating Margin: 48.3 dB

Try again, but this time do NOT use "-3" for the coax losses. The
spread sheet wants it without the minus sign. Use just "3". Remind
me to yell at YDI about that.

>It looks like the more gain in the antennas (7 x 2 = +14 dBi) balances
>perfectly the smaller Tx Power (1 - 15 = -14 dBm), is that correct?

No. It's an artifact of the extra minus sign.

Just to be sure, I cramming it into a more complex calculator at:
http://my.athenet.net/~multiplx/cgi-bin/wireless.main.c...
I get the same 36dB fade margin using my original numbers and 17dBi
antennas.

>Is the RX Signal Level (-35.7 dBm) too much?
>Will it overload the LinkSys WRT54GS receiver?

I don't know exactly where the broadcom chipset overloads. Older
bipolar chips overload at about -30dBm. However, I don't have numbers
on the newer Broadcom BiCMOS chips thanks to Broadcom controlling the
distribution of their data sheets. If I had a WRT54G box to play
with, I could put it on the bench and run a quick (rough) test.

>I have no idea about the overload point for the Broadcom chipset.
>There is no mention about it in the above datasheet.
>Any guess about it?

Yeah. This is a guess, this is only a guess. A similar BiCMOS chip
has a 3rd order intercept point (IP3) of -6dBm. Subtracting my guess
of the conversion gain and extrapolating the curves, that *ROGHLY*
yields an overload point about about -30dBm.
http://www.matrixtest.com/Literat/MTN109.htm

>As suggested, I should be able to simulate the effects by putting the
>two LinkSys boxes next to each other with the included omnidirectional
>antennas.

Yep. However, if you have an accurate attenuator, you can just plug
the antennas from two boxes into each other.
attenuator loss = +15dBm tx power - (-30dBm overload point) = 45dB
So, try a 40dB attenuator and see if you have problems.

>What would be the exact distance for simulating that signal level (-35.7
>dBm) or a little stronger?

Using what for antennas? If you get to close, you end up with a
near-field calculation instead of a far-field. I don't wanna grind
the numbers. Use the calculator at:
http://www.ydi.com/calculation/som.php
and try various numbers for the distance until you get -30dBm signal
at the receiver input.

>The reason for which I am considering to get the 24 dBi antennas instead
>of the 17 dBi ones (that would probably work fine too) is that I would
>like to get a full reliable 54 Mbps link, also consider the trees in the
>LOS, they will attenuate the signal ...

Trees are bad. Go for the 24dBi antennas.

>Also, it looks you can set the LinkSys WRT54GS transmit power from 0 to
>84 mW:
><http://docs.sveasoft.com/SV-Wireless-AdvancedSettings.h...;
>What would be the equivalent numbers in dB?

84mw = +19.2dBm. The data sheet power +18dBm. Close enough. Why
would you want to decrease it? Note that I used +15dBm for my power
output, not +19dBm. This is from personal experience with other
radios that never seem to deliver rated power. The test results on
the FCC web pile show a test power output of +16dbm for 802.11b and
+15dbm for 802.11g. See section 5.6 at:
https://gullfoss2.fcc.gov/prod/oet/forms/blobs/retrieve...

To keep this in perspective, a 6dB increase in system gain will double
your range. 3dB is worth 1.4 times the range.

>If I set it to 0 mW, will it transmit the radio signal at all?

I dunno.

>Basically I would like to run the LinkSys box at the minimum transmit
>power and take adavantage of the high gain parabolic antennas.

Methinks that's a bad idea. Your performance is determined by the
signal to noise ratio of the received signal. If you crank down the
xmit signal to any large degree, you won't have the required signal to
noise ratio necessary to maintain a link, much less get decent
thruput.

>Is it a good plan?

No.

>Thanks a lot, I am learning a lot from this ng.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
December 6, 2004 1:30:52 PM

Archived from groups: alt.internet.wireless (More info?)

On 12/5/04 9:58 PM, Jeff Liebermann wrote:

> That's the sensitivity of the chip, measured at the input to the chip
> and not the sensitivity measured after going through a diversity
> switch IC, across some lossy G10 circuit board, through a lossy coax
> cable, and into 1/2 of a lossy R-TNC pair. Use the sensitivity of the
> final product, not that of the chip.

I found some info about the WRT54G, the WRT54GS should be close:
<http://www.seattlewireless.net/index.cgi/LinksysWrt54g&...;
---
Receiver Sensitivity (unconfirmed):
* -65db for ofdm 802.11g 54 megs
* -80db for dsss 802.11b 11 megs
---

> Try again, but this time do NOT use "-3" for the coax losses. The
> spread sheet wants it without the minus sign. Use just "3". Remind
> me to yell at YDI about that.

Thanks, I get your results now.

> No. It's an artifact of the extra minus sign.

Removing the extra minus sign, I still get the same results by replacing
the 17 dBi antennas with the 24 dBi ones and setting the Tx Power to 1
dBm instead of 15 dBm.
Am I missing something?

> Just to be sure, I cramming it into a more complex calculator at:
> http://my.athenet.net/~multiplx/cgi-bin/wireless.main.c...
> I get the same 36dB fade margin using my original numbers and 17dBi
> antennas.

That looks a very good calculator, unfortunately it's a bit too complex
for me. :-)

> Yeah. This is a guess, this is only a guess. A similar BiCMOS chip
> has a 3rd order intercept point (IP3) of -6dBm. Subtracting my guess
> of the conversion gain and extrapolating the curves, that *ROGHLY*
> yields an overload point about about -30dBm.
> http://www.matrixtest.com/Literat/MTN109.htm

According to your guess (I know it's only a guess), the overload point
(about -30 dBm) would be about the same of the older bipolar chips.
I thought the LinkSys receiver was good quality ones, was I wrong? :-)

Anyway, removing the extra minus sign from the online calculator and
using 24 dBi antennas and 1 dBm Tx Power, I get a Rx Signal Level of
-47.7 dBm, that should be far enough from the estimated overload point.

> Yep. However, if you have an accurate attenuator, you can just plug
> the antennas from two boxes into each other.
> attenuator loss = +15dBm tx power - (-30dBm overload point) = 45dB
> So, try a 40dB attenuator and see if you have problems.

Unfortunately I don't have such attenuator, and even if I had it, I
don't think I have the experience to use it correctly.

> Using what for antennas? If you get to close, you end up with a
> near-field calculation instead of a far-field. I don't wanna grind
> the numbers. Use the calculator at:
> http://www.ydi.com/calculation/som.php
> and try various numbers for the distance until you get -30dBm signal
> at the receiver input.

I want to do such test using the omnidirectional antennas bundled with
the LinkSys WRT54GS boxes, but I am not sure of their gain, I cannot
find the specs for them. Any idea?

What is the difference between the near-field and the far-field
calculation? Will the YDI calculator take care of it automatically?

> Trees are bad. Go for the 24dBi antennas.

Yes, that's another good reason why I want to go for the 24 dBi antennas.

> 84mw = +19.2dBm. The data sheet power +18dBm. Close enough. Why
> would you want to decrease it? Note that I used +15dBm for my power
> output, not +19dBm. This is from personal experience with other
> radios that never seem to deliver rated power. The test results on
> the FCC web pile show a test power output of +16dbm for 802.11b and
> +15dbm for 802.11g. See section 5.6 at:
> https://gullfoss2.fcc.gov/prod/oet/forms/blobs/retrieve...
>
> To keep this in perspective, a 6dB increase in system gain will double
> your range. 3dB is worth 1.4 times the range.

The main reason because I want to decrease the TX Power is to avoid
getting too close to the overload point for the receiver.
Also the Italian laws don't allow high power radio signals like in the
U.S.A., actually I think all the E.U. countries have stricter limits for
that.

> I dunno.

BTW, it looks you can increase the LinkSys TX Power up to 251 mW:
<http://www.sveasoft.com/content/view/3/1/&gt;

I am almost sure the signal will not be clear at that power level, also
it will probably burn the box in the long run ...

> Methinks that's a bad idea. Your performance is determined by the
> signal to noise ratio of the received signal. If you crank down the
> xmit signal to any large degree, you won't have the required signal to
> noise ratio necessary to maintain a link, much less get decent
> thruput.

Okay, then what would be the minimum TX Power necessary to keep the
signal to noise ratio good and have a good link?

To sum up: my aim is to get a stable full 54 Mbps radio link at 340
meters with two 24 dBi parabolic antennas without overloading the
LinkSys receivers, and there are a couple of oak trees in the LOS.

Thanks, I keep learning a lot from your advice and from this newsgroup.
Anonymous
a b F Wireless
December 6, 2004 1:30:53 PM

Archived from groups: alt.internet.wireless (More info?)

On Mon, 06 Dec 2004 10:30:52 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>I found some info about the WRT54G, the WRT54GS should be close:
><http://www.seattlewireless.net/index.cgi/LinksysWrt54g&...;
>---
>Receiver Sensitivity (unconfirmed):
>* -65db for ofdm 802.11g 54 megs
>* -80db for dsss 802.11b 11 megs

I'm suspicious when someone uses dB instead of the correct dBm. The
numbers look real enough to be useful as they are "only" 2-3dB worse
than my stated numbers. That's within the accuracy of a BER (bit
error rate tester) and my ancient and uncalibrated test equipment.

>Removing the extra minus sign, I still get the same results by replacing
>the 17 dBi antennas with the 24 dBi ones and setting the Tx Power to 1
>dBm instead of 15 dBm.
>Am I missing something?

Why would you want to reduce the TX power from +15dBm to +1dBm? A
15dB drop in tx power is the equivalent of a 31 times drop in power
level. Stay with the 15dBm tx power.

>> Just to be sure, I cramming it into a more complex calculator at:
>> http://my.athenet.net/~multiplx/cgi-bin/wireless.main.c...
>> I get the same 36dB fade margin using my original numbers and 17dBi
>> antennas.

>That looks a very good calculator, unfortunately it's a bit too complex
>for me. :-)

There are others online that will work. The complex one above is what
I use when I have to deal with marginal systems running at the very
edge of the performance envelope. It's also a good learning tool. If
you can understand EVERY item on the page, you're well on your way to
understanding wireless propogation. (The rest is magic and
witchcraft).

Other fade margin calculators:
http://www.ecommwireless.com/calculations.html
http://www.tcstx.com/software/Flash/ThermalFadeMargin.s...
http://www.airaya.com/support/ai108_link.asp
http://www.cisco.com/application/vnd.ms-excel/en/us/gue...
http://www.n2end.com/store/calculator.xls

>According to your guess (I know it's only a guess), the overload point
>(about -30 dBm) would be about the same of the older bipolar chips.
>I thought the LinkSys receiver was good quality ones, was I wrong? :-)

BiCMOS and SiGe should be somewhat better than bipolar. GaAs should
be spectacularly better than bipolar. However, there are many ways to
screw things up. Most of the modern chipsets emphasize low power
consumption. At some point, the quest for low power consumption can
ruin the ability of the front end to handle overload. Modern designs
are also direct conversion receivers, which are quite different from
the older superhetrodyne style of double conversion receivers. Again,
the simplicity of direct conversion is paid for in overload handling.
If you're into this problem, CommDesign magazine has something on the
topic, but I don't wanna dig for it now.
http://www.commsdesign.com

>Anyway, removing the extra minus sign from the online calculator and
>using 24 dBi antennas and 1 dBm Tx Power, I get a Rx Signal Level of
>-47.7 dBm, that should be far enough from the estimated overload point.

Well, if you insist on reducing your power 30 times, sure. As I said
before, I do NOT think that overload will be a problem, especially
since you introduced a few trees in the way in the last message.
Trees are very lossy at 2.4Ghz and should reduce your signal to
tolerable levels.

>Unfortunately I don't have such attenuator, and even if I had it, I
>don't think I have the experience to use it correctly.

They're easy enough to find. The can also be made from cheap lossy
coax cable. As for expertise, Learn by Destroying(tm). Just
calculate how far you would need to be seperated to get -30dBm at the
receiver input. That you can do.

>I want to do such test using the omnidirectional antennas bundled with
>the LinkSys WRT54GS boxes, but I am not sure of their gain, I cannot
>find the specs for them. Any idea?

Yeah. Figure about 2.5dBi. I know that some data sheets claim 4dBi,
but my models show much less.

>What is the difference between the near-field and the far-field
>calculation? Will the YDI calculator take care of it automatically?

Big difference. In the near field, signal strength does NOT follow
square law. Normally in far field double the distance results in 1/4
the signal strength. In near field it's roughly linear. None of the
online calculators do near field.

>The main reason because I want to decrease the TX Power is to avoid
>BTW, it looks you can increase the LinkSys TX Power up to 251 mW:
><http://www.sveasoft.com/content/view/3/1/&gt;

Yeah, someone posted some really lousy spectrum analyzer photos of
what the spectra looks like when one does that. They left off the
grid markings and reference levels so I couldn't tell what was
happening or whether they met FCC emission requirements. Methinks
I'll pass on commenting more on such hacking until I determine if the
transmit spectra is really tolerable, or if it goes non-linear and
sprays trash all over the band.

>Okay, then what would be the minimum TX Power necessary to keep the
>signal to noise ratio good and have a good link?

About 20dB over the receiver sensitivity. That's your fade margin as
calculated on the various online calculators. Note that the
sensitivity changes with connection speed. Use your -65dBm for
802.11g at 54Mbits/sec. Add 20db resulting in -45dBm receive signal.

>To sum up: my aim is to get a stable full 54 Mbps radio link at 340
>meters with two 24 dBi parabolic antennas without overloading the
>LinkSys receivers, and there are a couple of oak trees in the LOS.
>
>Thanks, I keep learning a lot from your advice and from this newsgroup.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
Anonymous
a b F Wireless
December 7, 2004 1:12:09 PM

Archived from groups: alt.internet.wireless (More info?)

On 12/6/04 7:01 PM, Jeff Liebermann wrote:

> Why would you want to reduce the TX power from +15dBm to +1dBm? A
> 15dB drop in tx power is the equivalent of a 31 times drop in power
> level. Stay with the 15dBm tx power.

Okay, I'll do that. I still wonder what is the minimum TX power to get a
good signal, considering the signal to noise radio thing you told me ...

> BiCMOS and SiGe should be somewhat better than bipolar. GaAs should
> be spectacularly better than bipolar. However, there are many ways to
> screw things up. Most of the modern chipsets emphasize low power
> consumption. At some point, the quest for low power consumption can
> ruin the ability of the front end to handle overload. Modern designs
> are also direct conversion receivers, which are quite different from
> the older superhetrodyne style of double conversion receivers. Again,
> the simplicity of direct conversion is paid for in overload handling.
> If you're into this problem, CommDesign magazine has something on the
> topic, but I don't wanna dig for it now.
> http://www.commsdesign.com

I tried to search their web site, but no luck ...

> Well, if you insist on reducing your power 30 times, sure. As I said
> before, I do NOT think that overload will be a problem, especially
> since you introduced a few trees in the way in the last message.
> Trees are very lossy at 2.4Ghz and should reduce your signal to
> tolerable levels.

They are oak trees: they loose foliage in the fall/winter and the
attenuation will be much less than in spring/summer.

> Big difference. In the near field, signal strength does NOT follow
> square law. Normally in far field double the distance results in 1/4
> the signal strength. In near field it's roughly linear. None of the
> online calculators do near field.

Can you estimate the approximate distance between the two LinkSys boxes
to get a -30 dBm signal at the receiver input using the bundled antennas?

Can I damage the boxes if I put them too close?

Do you know if the WRT54GS has any feature to read the signal level at
the receiver input? I don't think you can do that from the web
interface, maybe it has some hidden command in the CLI?

> About 20dB over the receiver sensitivity. That's your fade margin as
> calculated on the various online calculators. Note that the
> sensitivity changes with connection speed. Use your -65dBm for
> 802.11g at 54Mbits/sec. Add 20db resulting in -45dBm receive signal.

Okay, then I would need a receive signal between -45 dBm (stable 54 MBps
link) and -30 dBm (estimated overload point).

According to the calculations, using 24 dBi antennas and 15 dBm transmit
power, the signal will be in that interval, then substract a few dBm for
the trees, yeah, I should be okay ...

I am going to order the 24 dBi parabolic antennas.
I'll let you know if the link works when I set it up ...

Thanks a lot for your advice.
Anonymous
a b F Wireless
December 13, 2004 1:13:10 PM

Archived from groups: alt.internet.wireless (More info?)

On 12/5/04 9:58 PM, Jeff Liebermann wrote:

> Yeah. This is a guess, this is only a guess. A similar BiCMOS chip
> has a 3rd order intercept point (IP3) of -6dBm. Subtracting my guess
> of the conversion gain and extrapolating the curves, that *ROGHLY*
> yields an overload point about about -30dBm.
> http://www.matrixtest.com/Literat/MTN109.htm

I found a PDF document about the Broadcom radio chipset specifications
and tests:
<http://www.hotchips.org/archive/hc15/pdf/11.broadcom.pd...;

Does it help to get a better estimation of the overload point for the
LinkSys WRT54GS radio receiver?

> Using what for antennas? If you get to close, you end up with a
> near-field calculation instead of a far-field. I don't wanna grind
> the numbers. Use the calculator at:
> http://www.ydi.com/calculation/som.php
> and try various numbers for the distance until you get -30dBm signal
> at the receiver input.

Can I permanently damage the LinkSys boxes if I put them too close each
other to find out the actual overload point?

"Learn by Destroying" is pretty cool, but these LinkSys boxes are pretty
expensive in Italy, I would prefer to not "brick" them for now! :-)

Thanks a lot.
Anonymous
a b F Wireless
December 13, 2004 1:13:11 PM

Archived from groups: alt.internet.wireless (More info?)

On Mon, 13 Dec 2004 10:13:10 +0100, meATprivacyDOTnet <me@privacy.net>
wrote:

>On 12/5/04 9:58 PM, Jeff Liebermann wrote:
>
>> Yeah. This is a guess, this is only a guess. A similar BiCMOS chip
>> has a 3rd order intercept point (IP3) of -6dBm. Subtracting my guess
>> of the conversion gain and extrapolating the curves, that *ROGHLY*
>> yields an overload point about about -30dBm.
>> http://www.matrixtest.com/Literat/MTN109.htm

>I found a PDF document about the Broadcom radio chipset specifications
>and tests:
><http://www.hotchips.org/archive/hc15/pdf/11.broadcom.pd...;

Actually, that's a PDF of a PowerPoint presentation. Buried in the
middle are some useful numbers. The BCM2050 chip (802.11g) has a 3rd
order intercept point (IIP3) of -16dBm at maximum gain and +4dBm and
minimum gain. You're going to be running near the middle to upper
part of the range, which puts you where I previous guessed, at -6dBm
IIP3 or better. That's roughly -30dBm or higher overload. Probably
higher.

>Does it help to get a better estimation of the overload point for the
>LinkSys WRT54GS radio receiver?

Sorta. I think you're eggagerating the effects of too much signal.
It isn't likely to be a problem, especially with trees in the way to
reduce the signal furthur. In addition, losses tend to be higher than
calculated, and antenna gains tend to be less than the manufacturer
specified.

>Can I permanently damage the LinkSys boxes if I put them too close each
>other to find out the actual overload point?

Nope. I have a WRT54Gv1.1 sitting on my desk, next to my BEFW11S4v4
and a WAP11v1.1. Antennas are almost touching. I'm playing with some
intereference tests. No fire, no smoke, no problems, and but plenty
of interaction.

>"Learn by Destroying" is pretty cool, but these LinkSys boxes are pretty
>expensive in Italy, I would prefer to not "brick" them for now! :-)

I went to the dump and recycling station yesterday and couldn't resist
scavenging some electronics out of the e-waste pile. Included was a
fairly dirty WRT54Gv1.1 that didn't power up. After cleaning, and
replacing a diode, capacitor, and power connector, and upgrading the
firmware, it works nicely. That's the way I like my wireless routers,
for free.


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
!