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Antennas

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Anonymous
a b F Wireless
December 3, 2004 10:12:58 PM

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

Hello all,

I am trying to set up a link, about 1/4 mile long. I have two radios,
each producing 200mw of power. I also am thinking about purchasing one
of two antennas -- one is 15dBi and the other is 24dBi. Different
people in the area have told me that for this link, all I need is a
15dBi antenna, but I am wondering if there would be any speed advantage
(or any advantages at all) to using a 24dBi antenna with this relatively
short link.

Thanks in advance,
Kevin Brown.

More about : antennas

December 3, 2004 11:28:15 PM

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

Kevin Brown wrote:

> Hello all,
>
> I am trying to set up a link, about 1/4 mile long. I have two radios,
> each producing 200mw of power. I also am thinking about purchasing one
> of two antennas -- one is 15dBi and the other is 24dBi. Different
> people in the area have told me that for this link, all I need is a
> 15dBi antenna, but I am wondering if there would be any speed advantage
> (or any advantages at all) to using a 24dBi antenna with this relatively
> short link.
>
> Thanks in advance,
> Kevin Brown.

If you have two radios producing 200mw and the power isn't watered down
by a bunch of connector and cable runs, you should be able to do a
quarter mile with far less than either 18 or 24dbi antennas. The main
advantage of the 24dbi I can think of is focusing the signal so that the
radios receive less interference from outside sources and radiate less
interference to surrounding areas. No speed advantage I would think, not
unless something is wrong.
Anonymous
a b F Wireless
December 4, 2004 4:39:51 AM

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

On Fri, 03 Dec 2004 19:12:58 -0600, Kevin Brown
<-NOSPAM-itismekevinb-NOSPAM-@hotmail.com> wrote:

>I am trying to set up a link, about 1/4 mile long. I have two radios,
>each producing 200mw of power. I also am thinking about purchasing one
>of two antennas -- one is 15dBi and the other is 24dBi. Different
>people in the area have told me that for this link, all I need is a
>15dBi antenna, but I am wondering if there would be any speed advantage
>(or any advantages at all) to using a 24dBi antenna with this relatively
>short link.

15dBi will work just fine. There are two benifits to using 24dBi
antennas. Thanks for not specifying the hardware so I have to do
guesswork.

1. Assuming you have enough signal strength, the signal level
necessary to get "full" speed from what I'm guessing is 802.11g
hardware. This is from a DI-624 but is probably close enough to your
unspecified hardware.
* 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)
Note that the signal level difference between tolerable speed
(9Mbits/sec = -87dBm) and the fastest (54Mbits/sec = -68dBm) is 19dB.
That's a HUGE difference in required signal. If you want speed, go
for all the signal strength you can get.

Also, the above sensitivities are for the threshold where the system
starts to generate errors. You don't wanna be running at the bitter
edge. Try for 20-30dB of overhead.

Run the numbers at:
http://www.ydi.com/calculation/som.php
using -68dBm for the receive sensitivity. Aim for a fade margin (SOM)
of about 20-30dB. See how much antenna gain it takes. With:
Distance = 0.25 miles
Tx power = 20dBm
Tx ant gain = 15dBi
Rx and gain = 15dBi
Tx cable loss = 3dB (including connectors)
RX cable loss = 3dB
RX sens = -68dBm (for 54mbits/sec)
I get a fade margin of 20dB. That's barely tolerable, but not
thrilling. The 24dBi antennas yield 38dB of fade margin, which is
more than enough. The magic number is somewhere between 15dBi and
24dBi.

2. Higher gain antennas have a more narrow beamwidth. A little
interference from nearby 802.11b/g and microwave ovens can really
trash the thruput. If you want to keep these things out of your link,
go for a narrow beamwidth antenna. Also position it to block signals
from potential problem areas.



--
# 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
Related resources
Anonymous
a b F Wireless
December 4, 2004 9:00:38 AM

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

> >I am trying to set up a link, about 1/4 mile long. I have two
radios,
> >each producing 200mw of power. I also am thinking about purchasing
one
> >of two antennas -- one is 15dBi and the other is 24dBi. Different
> >people in the area have told me that for this link, all I need is a
> >15dBi antenna, but I am wondering if there would be any speed
advantage
> >(or any advantages at all) to using a 24dBi antenna with this
relatively
> >short link.
>
> 15dBi will work just fine. There are two benifits to using 24dBi
> antennas. Thanks for not specifying the hardware so I have to do
> guesswork.

===
> 1. Assuming you have enough signal strength, the signal level
> necessary to get "full" speed from what I'm guessing is 802.11g
> hardware. This is from a DI-624 but is probably close enough to
your
> unspecified hardware.
> * 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)
> Note that the signal level difference between tolerable speed
> (9Mbits/sec = -87dBm) and the fastest (54Mbits/sec = -68dBm) is
19dB.
> That's a HUGE difference in required signal. If you want speed, go
> for all the signal strength you can get.
>
> Also, the above sensitivities are for the threshold where the system
> starts to generate errors. You don't wanna be running at the bitter
> edge. Try for 20-30dB of overhead.
>
> Run the numbers at:
> http://www.ydi.com/calculation/som.php
> using -68dBm for the receive sensitivity. Aim for a fade margin
(SOM)
> of about 20-30dB. See how much antenna gain it takes. With:
> Distance = 0.25 miles
> Tx power = 20dBm

200mw = 23dbm



> Tx ant gain = 15dBi
> Rx and gain = 15dBi
> Tx cable loss = 3dB (including connectors)
> RX cable loss = 3dB
> RX sens = -68dBm (for 54mbits/sec)
> I get a fade margin of 20dB. That's barely tolerable, but not
> thrilling. The 24dBi antennas yield 38dB of fade margin, which is
> more than enough. The magic number is somewhere between 15dBi and
> 24dBi.
>
> 2. Higher gain antennas have a more narrow beamwidth. A little
> interference from nearby 802.11b/g and microwave ovens can really
> trash the thruput. If you want to keep these things out of your
link,
> go for a narrow beamwidth antenna. Also position it to block
signals
> from potential problem areas.
>
>
>
> --
> # 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 4, 2004 12:58:50 PM

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

"Airhead" <campbell@alliancecable.net> wrote

> 200mw = 23dbm


Compared to what?

Ed Cregger
Anonymous
a b F Wireless
December 4, 2004 1:27:20 PM

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

On Sat, 4 Dec 2004 06:00:38 -0600, "Airhead"
<campbell@alliancecable.net> wrote:

>200mw = 23dbm

Oops. There went my aura of perfection. Add 3dB to the fade margin.
That would give 23dB for 15dBi antennas, and 41dB for 24dBi antennas.
15dBi would work, but I would still go for the 24dBi antennas.


--
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 4, 2004 1:54:20 PM

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

"The Amazing Seismo" <amazing_seismo@hotmail.com> wrote in message
news:cosjba01i0i@enews4.newsguy.com...
>
> "Airhead" <campbell@alliancecable.net> wrote
>
> > 200mw = 23dbm
>
The reference point of 0dbm = 1mw


>
> Compared to what?
>
> Ed Cregger
>
>
Anonymous
a b F Wireless
December 4, 2004 7:20:54 PM

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

Moochoes Grassy-ass. <G>

Ed Cregger


"Airhead" <campbell@alliancecable.net> wrote in message
news:41b1ec6a$0$793$2c56edd9@news.cablerocket.com...
>
> "The Amazing Seismo" <amazing_seismo@hotmail.com> wrote in
> message
> news:cosjba01i0i@enews4.newsguy.com...
>>
>> "Airhead" <campbell@alliancecable.net> wrote
>>
>> > 200mw = 23dbm
>>
> The reference point of 0dbm = 1mw
>
>
>>
>> Compared to what?
>>
>> Ed Cregger
>>
>>
>
>
Anonymous
a b F Wireless
December 5, 2004 2:26:14 AM

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

: Oops. There went my aura of perfection. Add 3dB to the fade margin.
: That would give 23dB for 15dBi antennas, and 41dB for 24dBi antennas.
: 15dBi would work, but I would still go for the 24dBi antennas.

I'm just wondering guys what are you doing.
Here, in Poland, we're making 11Mb (802.11b - DSSS) links for distances of few
kilometers using 30mW radios and 15dBi yagi's.

You're lucky that you can use more that our 100mW of EIRP :-)

cheers,
m.


--
Marcin Lukasik
Milea Wireless Communications, http://milea.pl
phone/fax/mobile: (++48) 13 4480070 / 13 4481148 / 509 390 490

,,the only difference between men and boys is the price of their toys''
Anonymous
a b F Wireless
December 5, 2004 2:26:15 AM

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

"Marcin Lukasik" <user@email.invalid> wrote in message
news:cotdo8$534$1@atlantis.news.tpi.pl...
>: Oops. There went my aura of perfection. Add 3dB to the
>fade margin.
> : That would give 23dB for 15dBi antennas, and 41dB for
> 24dBi antennas.
> : 15dBi would work, but I would still go for the 24dBi
> antennas.
>
> I'm just wondering guys what are you doing.
> Here, in Poland, we're making 11Mb (802.11b - DSSS) links
> for distances of few
> kilometers using 30mW radios and 15dBi yagi's.
>
> You're lucky that you can use more that our 100mW of EIRP
> :-)
>
> cheers,
> m.


What does the "I" stand for in EIRP? TIA

Ed Cregger
Anonymous
a b F Wireless
December 5, 2004 2:26:16 AM

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

"The Amazing Seismo" <amazing_seismo@hotmail.com> wrote:
>What does the "I" stand for in EIRP? TIA

Effective Isotropic Radiated Power

Google is your friend.
Anonymous
a b F Wireless
December 5, 2004 3:44:15 AM

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

<William P.N. Smith> wrote in message
news:9km4r0pr72b0cgkrbrcv5obg8vfforg32m@4ax.com...
> "The Amazing Seismo" <amazing_seismo@hotmail.com> wrote:
>>What does the "I" stand for in EIRP? TIA
>
> Effective Isotropic Radiated Power
>
> Google is your friend.
>


I was afraid that you were going to say that. Thanks.

Ed Cregger
Anonymous
a b F Wireless
December 5, 2004 4:02:47 AM

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

On Sat, 4 Dec 2004 09:58:50 -0500, "The Amazing Seismo"
<amazing_seismo@hotmail.com> wrote:

>"Airhead" <campbell@alliancecable.net> wrote
>
>> 200mw = 23dbm

>Compared to what?
>Ed Cregger

Commandment #11: Thou shalt not abrev.

The most common ones in use for wireless are:
dB = decibels as in a ratio.
For power, it's: dB = 10 * log(ratio)
dBm = decibels above 1 milliwatt into 50 ohms.
dBi = decibels above an isotropic (antenna) radiator.

There are plenty of other dB references (i.e. dBw, dBu, dBv, dbV, dBm,
dbVU, dBFS, dBspl, dBrnCO) and impedance references (50, 75, 600
ohms).


--
# 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 4:02:48 AM

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

It has been a while since I studied for the ancient FCC
commercial ticket exam. The old license, with radar
endorsement, still hangs upon the wall, somewhere in the
house.

In the "olden days", any spec referring to isotropic, point
source, antennas was considered marketing hype with copious
amounts of snake oil stirred into the mix. All serious
references were to a 1/2 wave dipole. Funny how time changes
everything.

Thanks for the memory stimulators.

Ed Cregger


"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in
message news:3pm4r0hu2ktctft8b50pvvmfac7p56u3pp@4ax.com...
> On Sat, 4 Dec 2004 09:58:50 -0500, "The Amazing Seismo"
> <amazing_seismo@hotmail.com> wrote:
>
>>"Airhead" <campbell@alliancecable.net> wrote
>>
>>> 200mw = 23dbm
>
>>Compared to what?
>>Ed Cregger
>
> Commandment #11: Thou shalt not abrev.
>
> The most common ones in use for wireless are:
> dB = decibels as in a ratio.
> For power, it's: dB = 10 * log(ratio)
> dBm = decibels above 1 milliwatt into 50 ohms.
> dBi = decibels above an isotropic (antenna) radiator.
>
> There are plenty of other dB references (i.e. dBw, dBu,
> dBv, dbV, dBm,
> dbVU, dBFS, dBspl, dBrnCO) and impedance references (50,
> 75, 600
> ohms).
>
>
> --
> # 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 4:02:49 AM

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

On Sun, 5 Dec 2004 00:50:42 -0500, "The Amazing Seismo"
<amazing_seismo@hotmail.com> wrote:

>It has been a while since I studied for the ancient FCC
>commercial ticket exam. The old license, with radar
>endorsement, still hangs upon the wall, somewhere in the
>house.

That must have been quite a while ago. The current incantation is the
GROL (General Radio Operators License):
http://www.narte.org/h/fccabout.asp
http://www.w5yi.org/page.php?id=35
It's now issued for a lifetime. It's basically the same as elements 1
and 3 that you probably took for the old 2nd class license, with a bit
of the old element 4 that was the old 1st class license. In other
words, it's easier than your previous ticket. The catch is that they
ask the questions in a rather odd manner so that you must know the
answer they are expecting, which is not necessarily correct or even
close. I had to borrow the study guide and temporarily revert to
college exam style memorization because of the odd question style.

>In the "olden days", any spec referring to isotropic, point
>source, antennas was considered marketing hype with copious
>amounts of snake oil stirred into the mix. All serious
>references were to a 1/2 wave dipole. Funny how time changes
>everything.

Using a dipole reference was fine before the days of computah modeling
(late 1970's) when antenna patterns were measured, not calculated,
usually with a dipole reference. This resulted in much abuse by
antenna manufactories in specifying the gain of a dipole over
isotropic. 2.15dB is the accepted figure, but that didn't stop
vendors from using other numbers or positioning their antennas so that
ground reflections would yield the highest gain.

All that changed with NEC antenna modeling. Measurd dipole over real
ground references made no sense when all the models are based on
isotropic radiators in free space. In my never humble opinion,
isotropic reference models are easier to deal with and do not involve
any creative number juggling. At least everyone will agree on the
gain of an isotropic radiator (0dBi) in free space.

>Thanks for the memory stimulators.

Keep going. Study for the GROL so that you will have more wallpaper.


--
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 5, 2004 4:18:41 AM

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

"The Amazing Seismo" <amazing_seismo@hotmail.com> wrote in message
news:cotl9002mhd@enews4.newsguy.com...
>
> "Marcin Lukasik" <user@email.invalid> wrote in message
> news:cotdo8$534$1@atlantis.news.tpi.pl...
> >: Oops. There went my aura of perfection. Add 3dB to the
> >fade margin.
> > : That would give 23dB for 15dBi antennas, and 41dB for
> > 24dBi antennas.
> > : 15dBi would work, but I would still go for the 24dBi
> > antennas.
> >
> > I'm just wondering guys what are you doing.
> > Here, in Poland, we're making 11Mb (802.11b - DSSS) links
> > for distances of few
> > kilometers using 30mW radios and 15dBi yagi's.
> >
> > You're lucky that you can use more that our 100mW of EIRP
> > :-)
> >
> > cheers,
> > m.
>
>
> What does the "I" stand for in EIRP? TIA
>
Effective Isotropic Radiated Power

isotropic.
exhibiting properties (as velocity of light transmission) with the same
values when measured along axes in all directions
Anonymous
a b F Wireless
December 5, 2004 7:20:05 AM

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

"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in
message news:04h5r09r1o059728g45fjlqr7qe6j6f5v0@4ax.com...
> On Sun, 5 Dec 2004 00:50:42 -0500, "The Amazing Seismo"
> <amazing_seismo@hotmail.com> wrote:
>
>>It has been a while since I studied for the ancient FCC
>>commercial ticket exam. The old license, with radar
>>endorsement, still hangs upon the wall, somewhere in the
>>house.
>
> That must have been quite a while ago. The current
> incantation is the
> GROL (General Radio Operators License):
> http://www.narte.org/h/fccabout.asp
> http://www.w5yi.org/page.php?id=35
> It's now issued for a lifetime. It's basically the same
> as elements 1
> and 3 that you probably took for the old 2nd class
> license, with a bit
> of the old element 4 that was the old 1st class license.
> In other
> words, it's easier than your previous ticket. The catch
> is that they
> ask the questions in a rather odd manner so that you must
> know the
> answer they are expecting, which is not necessarily
> correct or even
> close. I had to borrow the study guide and temporarily
> revert to
> college exam style memorization because of the odd
> question style.
>
>>In the "olden days", any spec referring to isotropic,
>>point
>>source, antennas was considered marketing hype with
>>copious
>>amounts of snake oil stirred into the mix. All serious
>>references were to a 1/2 wave dipole. Funny how time
>>changes
>>everything.
>
> Using a dipole reference was fine before the days of
> computah modeling
> (late 1970's) when antenna patterns were measured, not
> calculated,
> usually with a dipole reference. This resulted in much
> abuse by
> antenna manufactories in specifying the gain of a dipole
> over
> isotropic. 2.15dB is the accepted figure, but that didn't
> stop
> vendors from using other numbers or positioning their
> antennas so that
> ground reflections would yield the highest gain.
>
> All that changed with NEC antenna modeling. Measurd
> dipole over real
> ground references made no sense when all the models are
> based on
> isotropic radiators in free space. In my never humble
> opinion,
> isotropic reference models are easier to deal with and do
> not involve
> any creative number juggling. At least everyone will
> agree on the
> gain of an isotropic radiator (0dBi) in free space.
>
>>Thanks for the memory stimulators.
>
> Keep going. Study for the GROL so that you will have more
> wallpaper.


I have the GROL too. It got me a radio sales job once. 8>)

Ed Cregger
Anonymous
a b F Wireless
December 5, 2004 4:22:52 PM

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

I still have my First Class with radar endorsement around. Of
course, I have the General Class with radar now. I'm not sure that it
is really good for anything any more.

Regards,


Fred
Anonymous
a b F Wireless
December 5, 2004 4:22:53 PM

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

"Fred Atkinson" <fatkinson@mishmash.com> wrote in message
news:rn26r0p2qj4dldhh1q9ogtk9s5r8bfj7k7@4ax.com...
> I still have my First Class with radar endorsement around.
> Of
> course, I have the General Class with radar now. I'm not
> sure that it
> is really good for anything any more.
>
> Regards,
>
>
> Fred
>


Yep, I studied a course for the First Class ticket and
passed it. When I called the FCC office to schedule a test,
I learned that they had discontinued it and had introduced
the GROL. I should have taken the test in the late sixties
as I had planned, but it wasn't meant to be.

Odd that my GROL test was still mostly on vacuum tube
theory, but that was a good thing. Got the Radar endorsement
a few weeks later.

Last thing I heard was that they were using the Amateur
Extra class test for the GROL. I did get my Extra (1985)
before they lowered the code requirement. I got the first
ham ticket after the commercial ticket, by about a year.

It is sad to see the license for a vocation die. I remember
when having an FCC ticket was as good as gold.

Ed Cregger
Anonymous
a b F Wireless
December 5, 2004 5:52:52 PM

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

But,,,

Jeff,, the easist way to really look at antennas is the dbi
reference, but the problem with the isotropic dipole is just that,
it's a computer model,, then you come to the old standby,

figures don't lie, but liar's figure.

This happens alot in the antenna community one company's dbi figures
don't work like the other company's dbi. I have first hand knowledge
of this with the comparison of Equinox's 29dbi 5.8ghz grid parabolic
when compared to PacWireless's 25dbi 5.8 grid parabolic.

The difference was :

a 50-60% link at 14miles with the Equinox antenna and a 85-95% link
using the PacWirless antenna. Yup, the equinox antenna was rated
4dbi better than the pacwireless antenna,, ie 4db,, but in reality.

The pac wireless antenna blew the equinox antenna away,,,

I really wish that the world would go to the dbd rating, ( DB over a
real dipole } then we would have some 'real world' figures.

After talking the techs at Equinox, located in Michigan, I found out
that their TEST RANGE was located in New Jersey, and that they
NEVER had run the antenna on a test range because it meant flying
800-1000 miles to do the 'simple testing'..... they beleived the dbi
rating that there 'engineers' had given them.. so much for that,,

figures don't lie, but liar's figure,,


DBD forever , then they have something to compare it to instead of
comparing "antennas to computers"


Bob Smith
Robert Smith Consulting
Wisp Consulting and Installation (I love towers)
ARS NA6T (extra Class)
ARRL Life Member
1st licensed in 1958






On Fri, 03 Dec 2004 19:12:58 -0600, Kevin Brown
<-NOSPAM-itismekevinb-NOSPAM-@hotmail.com> wrote:

>Hello all,
>
>I am trying to set up a link, about 1/4 mile long. I have two radios,
>each producing 200mw of power. I also am thinking about purchasing one
>of two antennas -- one is 15dBi and the other is 24dBi. Different
>people in the area have told me that for this link, all I need is a
>15dBi antenna, but I am wondering if there would be any speed advantage
>(or any advantages at all) to using a 24dBi antenna with this relatively
>short link.
>
>Thanks in advance,
>Kevin Brown.
Anonymous
a b F Wireless
December 5, 2004 9:21:14 PM

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

It's either isotropic, or it's a dipole. It can't be both.
Isotropic radiators are imaginary point source radiators.

The Amazing Seismo



"Robert Smith Consulting - Bob Smith" <na6t@na6t.com> wrote
in message
news:8947r098s5pt40hc1nn1ub5e8qsmmsngk0@4ax.com...
>
> But,,,
>
> Jeff,, the easist way to really look at antennas is the
> dbi
> reference, but the problem with the isotropic dipole is
> just that,
> it's a computer model,, then you come to the old standby,
>
> figures don't lie, but liar's figure.
>
> This happens alot in the antenna community one company's
> dbi figures
> don't work like the other company's dbi. I have first
> hand knowledge
> of this with the comparison of Equinox's 29dbi 5.8ghz grid
> parabolic
> when compared to PacWireless's 25dbi 5.8 grid parabolic.
>
> The difference was :
>
> a 50-60% link at 14miles with the Equinox antenna and a
> 85-95% link
> using the PacWirless antenna. Yup, the equinox antenna
> was rated
> 4dbi better than the pacwireless antenna,, ie 4db,, but in
> reality.
>
> The pac wireless antenna blew the equinox antenna away,,,
>
> I really wish that the world would go to the dbd rating,
> ( DB over a
> real dipole } then we would have some 'real world'
> figures.
>
> After talking the techs at Equinox, located in Michigan, I
> found out
> that their TEST RANGE was located in New Jersey, and that
> they
> NEVER had run the antenna on a test range because it meant
> flying
> 800-1000 miles to do the 'simple testing'..... they
> beleived the dbi
> rating that there 'engineers' had given them.. so much for
> that,,
>
> figures don't lie, but liar's figure,,
>
>
> DBD forever , then they have something to compare it to
> instead of
> comparing "antennas to computers"
>
>
> Bob Smith
> Robert Smith Consulting
> Wisp Consulting and Installation (I love towers)
> ARS NA6T (extra Class)
> ARRL Life Member
> 1st licensed in 1958
>
>
>
>
>
>
> On Fri, 03 Dec 2004 19:12:58 -0600, Kevin Brown
> <-NOSPAM-itismekevinb-NOSPAM-@hotmail.com> wrote:
>
>>Hello all,
>>
>>I am trying to set up a link, about 1/4 mile long. I have
>>two radios,
>>each producing 200mw of power. I also am thinking about
>>purchasing one
>>of two antennas -- one is 15dBi and the other is 24dBi.
>>Different
>>people in the area have told me that for this link, all I
>>need is a
>>15dBi antenna, but I am wondering if there would be any
>>speed advantage
>>(or any advantages at all) to using a 24dBi antenna with
>>this relatively
>>short link.
>>
>>Thanks in advance,
>>Kevin Brown.
>
Anonymous
a b F Wireless
December 5, 2004 10:28:25 PM

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

On Sun, 05 Dec 2004 14:52:52 -0800, Robert Smith Consulting - Bob
Smith <na6t@na6t.com> wrote:

>But,,,

Oh-oh. You've found where I've been hiding.

>Jeff,, the easist way to really look at antennas is the dbi
>reference, but the problem with the isotropic dipole is just that,
>it's a computer model,, then you come to the old standby,

As usual, I beg to differ. Many clueless companies simply subtract
2.15dB from the isotropic gain rating to yield dB over a dipole.

>figures don't lie, but liar's figure.

Everyone lies, but that's ok because nobody listens.

>This happens alot in the antenna community one company's dbi figures
>don't work like the other company's dbi.

Sorta. I've had the ratings on one of my ancient designs tweaked by
marketing. The short version is that I wanted to keep the return loss
under 15dB (about 1.5:1 vswr) and the built in filter group delay
constant within about +/- 10nsec over the 2.4GHz ISM band. That's not
easy to do with a high gain antenna. The result was that I had to
compromise on the gain specs. Although it did everything the customer
wanted, the lousy gain spec made it look like an inferior antenna. So
when marketing decided that there was a potential market, they just
changed the gain spec to be the same as a similar size competitors
antenna.

>I have first hand knowledge
>of this with the comparison of Equinox's 29dbi 5.8ghz grid parabolic
>when compared to PacWireless's 25dbi 5.8 grid parabolic.

You're comparing apples and oranges. Equinox make reflectors for use
with Motorola Canopy products. None of their antennas have feeds or
pigtails. The 29dBi gain is based on the reflector itself, without
the usual -3dB reflection loss, illumination losses, VSWR, etc. They
finally got smart and derated their antennas to the "common" 24dBi
gain spec used by similar sized antennas.
http://www.rfeq.com/images/warm_photo_large.jpg

http://www.rfeq.com/package_warm.php?id=a1194ba9955a541...

PacWireless doesn't make such a Canopy reflector. So my guess(tm) is
that you were testing:
http://www.pacwireless.com/products/directional.shtml
which includes the feed and pigtail.

The problem with the Equinox reflector has less to do with the gain of
the dish portion than with the gross inefficiency of the Canopy radio
illuminating the dish. My guess(tm) is that there is considerable
overspray from the Canopy internal antenna, and that's why your gain
and performance stunk.

>a 50-60% link at 14miles with the Equinox antenna and a 85-95% link
>using the PacWirless antenna. Yup, the equinox antenna was rated
>4dbi better than the pacwireless antenna,, ie 4db,, but in reality.

Yep. About what I would expect with an inefficient dish feed.

>The pac wireless antenna blew the equinox antenna away,,,

I've used lots of PacWireless dishes. They work. However, I prefer
the more expensive cast aluminium dishes instead of the painted steel.
Incidentally, remind me to show you my do it thyself corner reflector
made from welded steel storage shelves (Creative Cubes). Same
material as PacWireless but MUCH cheaper.

>I really wish that the world would go to the dbd rating, ( DB over a
>real dipole } then we would have some 'real world' figures.

I don't think it will make much difference. I can lie as well in dBd
as I can in dBi. However, I'm a believer in testing to verify the
computer calculations, not the other way around. I grind the numbers
on the NEC design program, and then verify that my construction
technique matches the calcs. If not, I find whatever I screwed up and
fix it. Back in the dark ages B.C. (before computers), my numerical
guesswork was far worse than today, when I have a decent modeling
program to play with.

>After talking the techs at Equinox, located in Michigan, I found out
>that their TEST RANGE was located in New Jersey, and that they
>NEVER had run the antenna on a test range because it meant flying
>800-1000 miles to do the 'simple testing'..... they beleived the dbi
>rating that there 'engineers' had given them.. so much for that,,

Well, yeah. That happens with "distributors and resellers" that don't
have testing facilities. In this case, it appears that Equinox did
run a field test on their 24dBi reflector:
http://www.rfeq.com/pdf/warm_24r_5.7.pdf
Sure looks like real data to me.

>figures don't lie, but liar's figure,,
>DBD forever , then they have something to compare it to instead of
>comparing "antennas to computers"

>Bob Smith
>Robert Smith Consulting
>Wisp Consulting and Installation (I love towers)

Masochist. Towers are for suicidal maniacs, indestructible kids, and
lynchings. My tower climbing days are over. With all the safety
paraphernalia required these days, I just let the "certified" and
insured tower climber do the dirty work.

>ARS NA6T (extra Class)

AE6KS (Extra Class or no class whatsoever).

>ARRL Life Member

That reminds me. Time to haul off all the old QST magazines.

>1st licensed in 1958

Ok, you beat me. Novice in about 1960 at age 12.


--
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 9:11:02 AM

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

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

> I can lie as well in dBd as I can in dBi.

As in "lies, damn lies, and tech specs"?
Anonymous
a b F Wireless
December 7, 2004 12:31:46 AM

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

I found out the little trick with the cheeeeap telescope from the
wireless list about a year ago, it works with dishes and parabolics..

I keep it under my hat,, you know "black magic",,

about Pac Wireless, they are in Utah now, building , designing and
shipping from one location, courtesy of the State of California
TAXES..

Well, were straying way off the original topic, so

next subject,,,,,


good talking to you jeff, I'll call you on the telephone this week and
we can catch up of things,,

see ya in the funnies,


Bob


On Fri, 03 Dec 2004 19:12:58 -0600, Kevin Brown
<-NOSPAM-itismekevinb-NOSPAM-@hotmail.com> wrote:

>Hello all,
>
>I am trying to set up a link, about 1/4 mile long. I have two radios,
>each producing 200mw of power. I also am thinking about purchasing one
>of two antennas -- one is 15dBi and the other is 24dBi. Different
>people in the area have told me that for this link, all I need is a
>15dBi antenna, but I am wondering if there would be any speed advantage
>(or any advantages at all) to using a 24dBi antenna with this relatively
>short link.
>
>Thanks in advance,
>Kevin Brown.
!