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PLEASE HELP - Need advise (thats legal!)

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Anonymous
June 25, 2004 1:27:12 AM

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

I am trying to create a multi-point wireless network. The main server
will be 10km away. I do have LOS. This sight will be having a
OMNI-DIRECTIONAL antenna about 80ft above the ground (to clear and
obstuctions). Once of the recieving ends (which is 10km away) will be
using a 24dBi parabolic Andrew antenna to try and link to the
OMNI-DIRECTIONAL antenna. Here is our delema.... We first considered
using a 15.4dBi omni 70inch antenna (from fab-corp.com) with a 1w
outdoor amp linked to a 200mw Long-Range 802.11b router. After finding
out that this was ILLEGAL.... (I'm assuming that it is harmful to ones
health). I would like to ask the experts in this group what is the
MOST powerful antenna I can use without breaking the law or causing
any kind of health concerns to prelonged exposure.

BTW: Here is some more info on the setup.
Both routers are the same (200mw Long Range 802.11b routers from
fab-corp.com)
24 dBi Andrew parabolic antenna (for the recieving end)
both routers will be using 1ft low loss cable from antenna to router
Also... from what I've read in this group... a 6dBi omni looks like
the maximum legal limit for this amp. So my question is.... would the
6dBi omni with the 1w amp be better than the 15.4dBi omni without the
amp???? If there is any better combo... please let me know.


Thanks!

More about : advise legal

Anonymous
June 25, 2004 12:52:20 PM

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

> will be 10km away. I do have LOS. This sight will be having a
> OMNI-DIRECTIONAL antenna about 80ft above the ground (to clear and

Why will one end have an omni directional antenna? I don't follow that,
you should be using 2 directional antennas for a point to point link.

> the maximum legal limit for this amp. So my question is.... would the
> 6dBi omni with the 1w amp be better than the 15.4dBi omni without the
> amp???? If there is any better combo... please let me know.

I'm not in your country but I think you'll find that 2 24dBi parabolic
antennas will do the link without any amplification anyway for that
distance.

David.
Anonymous
June 25, 2004 1:22:24 PM

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

David,

I have to repeat myself 1 million times everytime I post........ I
know 2 directional antennas would be more than enough.... for a point
to point. But this is NOT a point to point connection. This is a point
to MULTIPOINT connection....like I said earlier. I MUST (1000%
certainty) have a omni antenna on one end.


Thanks.... and please advise.
Related resources
June 25, 2004 4:58:02 PM

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

Kingz#1 wrote:
> I am trying to create a multi-point wireless network. The main server
> will be 10km away. I do have LOS. This sight will be having a
> OMNI-DIRECTIONAL antenna about 80ft above the ground (to clear and
> obstuctions). Once of the recieving ends (which is 10km away) will be
> using a 24dBi parabolic Andrew antenna to try and link to the
> OMNI-DIRECTIONAL antenna. Here is our delema.... We first considered
> using a 15.4dBi omni 70inch antenna (from fab-corp.com) with a 1w
> outdoor amp linked to a 200mw Long-Range 802.11b router. After finding
> out that this was ILLEGAL.... (I'm assuming that it is harmful to ones
> health). I would like to ask the experts in this group what is the
> MOST powerful antenna I can use without breaking the law or causing
> any kind of health concerns to prelonged exposure.
>
> BTW: Here is some more info on the setup.
> Both routers are the same (200mw Long Range 802.11b routers from
> fab-corp.com)
> 24 dBi Andrew parabolic antenna (for the recieving end)
> both routers will be using 1ft low loss cable from antenna to router
> Also... from what I've read in this group... a 6dBi omni looks like
> the maximum legal limit for this amp. So my question is.... would the
> 6dBi omni with the 1w amp be better than the 15.4dBi omni without the
> amp???? If there is any better combo... please let me know.
>
>
> Thanks!

Most people I know in the business stay away from amps unless it's the
*only* way to get it to work. Amps amplify noise equally with signal,
they don't always help. With 200mw radios, a 15dbi omni and a 24dbi
parabolic, I can hardly imagine you having problems getting a 10km link
to work unless there is a lot of 2.4GHz noise in the area already or you
have problems aiming the omni (you do know high-gain omnis have a rather
flat doughnut shaped radiation pattern, don't you?) Done a site survey yet?
June 26, 2004 3:36:14 PM

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

mikeycp3@yahoo.com (Kingz#1) wrote in news:4d451e16.0406250822.48f38c00
@posting.google.com:

> David,
>
> I have to repeat myself 1 million times everytime I post........ I
> know 2 directional antennas would be more than enough.... for a point
> to point. But this is NOT a point to point connection. This is a point
> to MULTIPOINT connection....like I said earlier. I MUST (1000%
> certainty) have a omni antenna on one end.
>
>
> Thanks.... and please advise.
>

The max TX power is 36 dBm. So base your calculation's on that. 200 mW is
23 dBm. Assuming that the antenna is connected directly to the box, the
greatest gain antenna would be 13 dBi. Now you have to account for cable
loss. Cheap coax is high loss, low loss coax is expensive. The coax specs
will give a loss per foot, or meter.

If you axe the amp and go with the 15 db omni, and can manage only 2+ dB of
coax loss, you'll be at max. This can be done by mounting the device in a
nema box on the mast and using the PoE. I can only assume that you were
looking at the one titled: Long Range 802.11b Multi-Client Bridge & POE
Inj.

Almost always better off not using an amp. Why add cost, another point of
failure, and more complexity if you can get the same result's with a more
simple approach.

Also, while it's true that directional antenna's do focus the RF energy,
there is still side lobes that vary from design to design. These lobes can
be used to make successful connection's also as long as the system is
planned that each subscriber units operates at similar power levels.

Of couse, I was in at an ISP that had all type's of antenna's & coax's
available to use to mix and match as necessary, so that made it quite a bit
easier.......
Anonymous
June 26, 2004 4:19:17 PM

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

"Kingz#1" <mikeycp3@yahoo.com> schreef in bericht
news:4d451e16.0406242027.398f1029@posting.google.com...
> I am trying to create a multi-point wireless network. The main server
> will be 10km away. I do have LOS. This sight will be having a
> OMNI-DIRECTIONAL antenna about 80ft above the ground (to clear and
> obstuctions). Once of the recieving ends (which is 10km away) will be
> using a 24dBi parabolic Andrew antenna to try and link to the
> OMNI-DIRECTIONAL antenna. Here is our delema.... We first considered
> using a 15.4dBi omni 70inch antenna (from fab-corp.com) with a 1w
> outdoor amp linked to a 200mw Long-Range 802.11b router. After finding
> out that this was ILLEGAL.... (I'm assuming that it is harmful to ones
> health). I would like to ask the experts in this group what is the
> MOST powerful antenna I can use without breaking the law or causing
> any kind of health concerns to prelonged exposure.
>
> BTW: Here is some more info on the setup.
> Both routers are the same (200mw Long Range 802.11b routers from
> fab-corp.com)
> 24 dBi Andrew parabolic antenna (for the recieving end)
> both routers will be using 1ft low loss cable from antenna to router
> Also... from what I've read in this group... a 6dBi omni looks like
> the maximum legal limit for this amp. So my question is.... would the
> 6dBi omni with the 1w amp be better than the 15.4dBi omni without the
> amp???? If there is any better combo... please let me know.
>
>
> Thanks!

Your combined specifications are difficult to meet: multipoint wireless + 10
km distance + legal solution.
I guess that you need to let one spec go to make this work. The legal aspect
might be tied to health issues,
though I'd rather think it is a matter of interference. Wireless signals do
interfere and your strong signal
will disturb all the weaker ones it finds in its path. Depending on your
location, you might get away
with strong signales, as long as nobody else suffers. I live in the
Netherlands and for sure it would
be cause for complaints.
Signal amplification is the last thing I'd pursue. At the omnidirectional
side, the antenna receives a lot
of noise and that gets amplified as well. Amplifiers don't change the signal
to noise ratio, they make
it even worse.
Basically the only advice here is to change the multipoint design to a
collection of point-to-point
connections. It is very likely that you don't want to hear that, but please
remember that multipoint
is equivalent to a a single point of failure. Not a good design, but YMMV,
Hans
Anonymous
June 27, 2004 2:12:57 AM

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

> I have to repeat myself 1 million times everytime I post........ I
> know 2 directional antennas would be more than enough.... for a point

Well, it wasn't clear to me, you only mentioned two locations!

> to point. But this is NOT a point to point connection. This is a point
> to MULTIPOINT connection....like I said earlier. I MUST (1000%
> certainty) have a omni antenna on one end.

Why? If you have say 3 sites, use two access points in the middle site
and use two DIRECTIONAL antennas, one pointing to each of the remote
sites.

How many other sites are there?

David.
Anonymous
June 27, 2004 2:14:27 AM

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

> Basically the only advice here is to change the multipoint design to a
> collection of point-to-point
> connections. It is very likely that you don't want to hear that, but please
> remember that multipoint
> is equivalent to a a single point of failure. Not a good design, but YMMV,

Quite, that's two of us saying the same thing so it must be true! :) 

David.
Anonymous
June 27, 2004 10:01:07 AM

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

"Fresnel Fadermargini" <RSSI@pathloss.dbm.com> wrote in message
news:z7sDc.2754$OR4.273210@twister.tampabay.rr.com...
> 1rst problem is it looks like you will be using conventional, 802.11 for
> a multi-point system and you are going to get burnt by Hidden Node...
> Although if done correctly, all child sites will hear the parent the
> children will
> not hear eachother, and since 802.11 uses CSMA, they will talk at the
same
> time..
> CSMA works by a client listening, and if clear it talks.. if it hears
> another system talking,
> the client backs off for longer and longer periods of time.. i.e.
> remember back in the
> Ethernet HUB days "collisions" This is how 802.11 works..

Wired Ethernet uses CSMA/CD (Carrier Sense, Multiple Access with Collision
DETECTION) and works as you described. 802.11 used CSMA/CA (CSMA with
Collision AVOIDANCE) and doesn't suffer from collisions nearly as often as
wired Ethernet.

Ron Bandes, CCNP, CTT+, etc.
Anonymous
June 27, 2004 2:52:37 PM

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

"David Taylor" <djtaylor@bigfoot.com> schreef in bericht
news:MPG.1b47f78cde5b5bd989c8b@news.individual.de...
> > Basically the only advice here is to change the multipoint design to a
> > collection of point-to-point
> > connections. It is very likely that you don't want to hear that, but
please
> > remember that multipoint
> > is equivalent to a a single point of failure. Not a good design, but
YMMV,
>
> Quite, that's two of us saying the same thing so it must be true! :) 
>
> David.

Saw your post too; obviously a case of great minds thinking alike, right ;-)
I have no clue why the OP is so sure that an omnidirectional antenna is the
only solution. OTOH he didn't really tell us what problem he's trying to
solve.
So unless the OP provides us with a little moer background this topic is
closed.

Hans
Anonymous
June 27, 2004 10:28:49 PM

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

See Below

"Ron Bandes" <RunderscoreBandes @yah00.com> wrote in message
news:D otDc.12571$OT6.8073134@news4.srv.hcvlny.cv.net...
> "Fresnel Fadermargini" <RSSI@pathloss.dbm.com> wrote in message
> news:z7sDc.2754$OR4.273210@twister.tampabay.rr.com...
> > 1rst problem is it looks like you will be using conventional, 802.11 for
> > a multi-point system and you are going to get burnt by Hidden Node...
> > Although if done correctly, all child sites will hear the parent the
> > children will
> > not hear eachother, and since 802.11 uses CSMA, they will talk at the
> same
> > time..
> > CSMA works by a client listening, and if clear it talks.. if it hears
> > another system talking,
> > the client backs off for longer and longer periods of time.. i.e.
> > remember back in the
> > Ethernet HUB days "collisions" This is how 802.11 works..
>
> Wired Ethernet uses CSMA/CD (Carrier Sense, Multiple Access with Collision
> DETECTION) and works as you described. 802.11 used CSMA/CA (CSMA with
> Collision AVOIDANCE) and doesn't suffer from collisions nearly as often as
> wired Ethernet.
>
> Ron Bandes, CCNP, CTT+, etc.
>
>
>
Ron, I think you need to do a bit of research on Hidden Node... Hence the
reason for polling/clocking MP systems.. I have been working in the space
for 17 years!
The Collision Avoidance part is where the Client listens first... but if a
client can not hear
another client oh well it talks... RTS/CTS was a weak attempt at solving
this issue..
It slowed down throughput and only worked for limited # of uers with packets
within a
certain size.

-FF
Expired CCIE, SMRE (Harris Senior Microwave RF Engineer)
(since you list your certs :)  )
Anonymous
June 27, 2004 10:28:50 PM

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

On Sun, 27 Jun 2004 18:28:49 GMT, "Fresnel Fadermargini"
<RSSI@pathloss.dbm.com> wrote:

>Ron, I think you need to do a bit of research on Hidden Node... Hence the
>reason for polling/clocking MP systems.. I have been working in the space
>for 17 years!

Yep. Hidden nodes are a killer. Lots of token passing, round robin,
polling, sychronous, and scanning type of solutions are available from
various proprietary (non-802.11) vendors. While none of these do
anything useful for small systems, large WISP (wireless ISP) systems
can really benefit from an improved collision
detection/avoidance/mitigation/bandwidth-allocation/whatever
mechanism.

Here's some graphs on the effects of collisions compared with a
polling scheme.
http://aqua.comptek.ru/test/HiddenNode/hidden_node_en.h...

Here's an open source attempt at a solution:
http://frottle.sourceforge.net
which uses QoS to allocate transmission bandwidth in order to reduce
collisions.

>The Collision Avoidance part is where the Client listens first... but if a
>client can not hear
>another client oh well it talks... RTS/CTS was a weak attempt at solving
>this issue..
>It slowed down throughput and only worked for limited # of uers with packets
>within a
>certain size.

Yep. It makes no sense to send flow control packets for small data
packet sizes. The overhead of the flow control packets is bad enough,
especially since they're sent at 1Mbit/sec (so ever radio can decode
them) in 802.11b. The radios have a CTS threshold setting. It just
sends the data for data packets smaller than the threshold, and does
the flow control exercise for larger packets. I wouldn't call it
weak, but it certainly doesn't solve all the collision problems under
all the circumstanced.

>-FF
>Expired CCIE, SMRE (Harris Senior Microwave RF Engineer)
> (since you list your certs :)  )

Ummm... No certifications, memberships, or titles. I never had time
to collect those and never needed them. Been doing radios in one form
or other (service, design, marketing, management, politics) since
about 1971. I added computahs to the mix in about 1981.



--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D 831-336-2558
Santa Cruz CA 95060 AE6KS
Anonymous
July 3, 2004 2:10:27 PM

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

Your biggest problem isn't legal limits... it's attenuation. What is the
length of transmission line that you will be using? Assuming a ground level
location for your WAP, the signal to and from the antenna will be so
degraded by feed line attenuation it will be un acceptable. Mounting the
WAP in a weather proof enclosure directly at the antenna's feed point will
help this issue. Run your network cable to the WAP at the antenna. This has
worked well for me on numerous commercial installations I have performed. Be
advised that every country has differing limitations on the ERP (effective
radiated power). You need to check the regulations in your country ( in the
United States the relevant document is FCC Part 15) and calculate the ERP of
your installation, and adjust power accordingly (adjusting feed line length
to attenuate the sufficient amount of RF is a very practical method).
point of info: you do not need to use an omni antenna for multipoint
access... 'stacked' directional antennas would be a better choice. The
directional antennas should be chosen for beam widths (radiation patterns)
and mounting so that they act as a single super high gain omni, that will
increase the reception as well as transmission. There are many commercially
made antennas that fit this description that would be preferable to a single
high gain omni

"Kingz#1" <mikeycp3@yahoo.com> wrote in message
news:4d451e16.0406250822.48f38c00@posting.google.com...
> David,
>
> I have to repeat myself 1 million times everytime I post........ I
> know 2 directional antennas would be more than enough.... for a point
> to point. But this is NOT a point to point connection. This is a point
> to MULTIPOINT connection....like I said earlier. I MUST (1000%
> certainty) have a omni antenna on one end.
>
>
> Thanks.... and please advise.
!