Omni antenna help please

Does anyone know what the highest gain omni antenna is?
Also, does Comet make decent omnis? Thanks.

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(E-Mail Removed) hath wroth:

>Does anyone know what the highest gain omni antenna is?

About 15.5dBi for 2.4GHz. 70" long:
<http://www.fab-corp.com/product.php?productid=489&cat=250&page=1>

>Also, does Comet make decent omnis? Thanks.

Yes, they're usually fine antennas.

In my never humble opinion, omni's are a bad idea. The vertical half
power beamwidth is conveniently missing from the data sheet. My guess
is that it's probably about 3 degrees or less. That's VERY narrow.

Let's play with the numbers. With a 3 degree downtilt, and mounted
50ft off the ground, your usable coverage area is from 0.13 to 0.36
miles (686ft to 1900ft). Hopefully, that's not what you want.
<http://www.terabeam.com/support/calculations/downtilt-cover.php>
Plug in your own numbers and see what you get.

That also means you have to mount the antenna absolutely perfectly
vertically.

There's also the problem of bandwidth. Very high gain antennas tend
to be very narrow band. I doubt that the antenna will cover the
entire 83.5MHz of the 2.4GHz band with a decent VSWR. It's hard to
tell because Comet doesn't supply any test data.

Hmmm... The 15dBi model isn't even listed on the Comet web pile:
<http://www.cometantenna.com/products.php?CatID=2&famID=15&childID=24>


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Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann <(E-Mail Removed)> hath wroth:

>About 15.5dBi for 2.4GHz. 70" long:
><http://www.fab-corp.com/product.php?productid=489&cat=250&page=1>
(...)
>Hmmm... The 15dBi model isn't even listed on the Comet web pile:
><http://www.cometantenna.com/products.php?CatID=2&famID=15&childID=24>

The plot thickens. I can see why it's missing. The data sheet for
the 12dBi model is at:
<http://www.cometantenna.com/pdfs/gp-24%20spec%20sheet.pdf>
The overall length from the data sheet and the above URL are both 70".
That's the same as the Fab-Corp 15dBi antenna. That's impossible
because omni antennas double in length for every 3dB of gain. What
that means is that the 70" antenna is NOT a 15dBi antenna and is
really a 12dBi antenna. That also explains why there's no 15dBi model
on the Comet web pile.

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


--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Thank you Jeff I really appreciate the honesty. I am currently using
an antenna I bought from Pasadena, it's a 40" omni they claim to
have 14db but I don't see it for sale any longer. I assume the
Comet omni units are vertical polarization, correct? Thank you.



Jeff Liebermann <(E-Mail Removed)> wrote:
> Jeff Liebermann <(E-Mail Removed)> hath wroth:
>
> >About 15.5dBi for 2.4GHz. 70" long:
> ><http://www.fab-corp.com/product.php?productid=489&cat=250&page=1>
> (...)
> >Hmmm... The 15dBi model isn't even listed on the Comet web pile:
> ><http://www.cometantenna.com/products.php?CatID=2&famID=15&childID=24>
>
> The plot thickens. I can see why it's missing. The data sheet for
> the 12dBi model is at:
> <http://www.cometantenna.com/pdfs/gp-24%20spec%20sheet.pdf>
> The overall length from the data sheet and the above URL are both 70".
> That's the same as the Fab-Corp 15dBi antenna. That's impossible
> because omni antennas double in length for every 3dB of gain. What
> that means is that the 70" antenna is NOT a 15dBi antenna and is
> really a 12dBi antenna. That also explains why there's no 15dBi model
> on the Comet web pile.
>
> Everyone lies, but that's ok, because nobody listens.

--
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(E-Mail Removed) hath wroth:

>Thank you Jeff I really appreciate the honesty. I am currently using
>an antenna I bought from Pasadena, it's a 40" omni they claim to
>have 14db but I don't see it for sale any longer. I assume the
>Comet omni units are vertical polarization, correct? Thank you.

<http://www.wlanparts.com>
I suspect you can call or write them and get the specs on whatever you
have. 40" and 14dBi seems a bit high. I have an Antenna Specialists
ASPT2976 omni antenna handy. It's about 2ft long and has a measured
gain of 8dbi gain. I've measured this several ways and it's within
0.5dB of 8dBi.

If I use this antenna as a reference standard, and the antenna guts
were the same construction, and I assume that the gain doubles (3dB)
for doubling the length of the antenna, then the gains would be:

Length gain radiation angle:
24" 8dBi 11 deg
48" 11dBi 5.5 deg
96" 14dBi 2.8 deg

Draw your own conclusions, but it looks like 70" lands at about 12dBi
as the data sheet suggests. 15dBi rediculous.

I don't think my previous comments sunk in. So, I'll be blunt. High
gain vertical omni antennas are awful for just about all but a few
specific applications. You haven't bothered to specify yours, so I
can't tell if this is going to work for you.

Also, yes. If it's a fairly thin vertical fiberglass tube, it's
undoubtably a vertically polarized antenna. Horizontally polarized
omnis are basically slotted waveguides and are much wider.

1:30AM Yawn...

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann <(E-Mail Removed)> hath wroth:

>I don't think my previous comments sunk in. So, I'll be blunt. High
>gain vertical omni antennas are awful for just about all but a few
>specific applications. You haven't bothered to specify yours, so I
>can't tell if this is going to work for you.

I forgot to plug my favorite antenna system. Look into Franklin or
AMOS sector antennas. See:
<http://pe2er.nl/wifisector>
<http://www.qsl.net/yu1aw/vhf_ant.htm>
<http://yu1aw.ba-karlsruhe.de/ANT.htm>
<http://www.brest-wireless.net/gallery/AntenneAmos>
<http://www.brest-wireless.net/wiki/materiel:amos>
Lots of gain, very small vertical radiation angle, fairly wide
horizontal coverage (90 to 120 degrees). They're easy to build, but
there are commercial versions if prefer.



--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Mon, 16 Jul 2007 01:34:13 -0700, Jeff Liebermann <(E-Mail Removed)>
wrote:

>I don't think my previous comments sunk in. So, I'll be blunt. High
>gain vertical omni antennas are awful for just about all but a few
>specific applications. You haven't bothered to specify yours, so I
>can't tell if this is going to work for you.

I use them on my boat for hitting shore based APs. Since the boat is
constantly swinging at anchor an omni antenna is absolutely essential,
and the higher the gain the better. I have sometimes been able to
connect with good outdoor APs that were over 4 miles away.

This is the one I'm using at the moment:

http://wlanparts.com/product/GP-24-3

High gain omnis are also useful at APs where wide outdoor coverage is
needed.

That is the antenna that I want to buy. I bought the 14db, 40 inch
from them and I am using it now and it seems to work great.




Wayne.B <(E-Mail Removed)> wrote:
> On Mon, 16 Jul 2007 01:34:13 -0700, Jeff Liebermann <(E-Mail Removed)>
> wrote:
>
> >I don't think my previous comments sunk in. So, I'll be blunt. High
> >gain vertical omni antennas are awful for just about all but a few
> >specific applications. You haven't bothered to specify yours, so I
> >can't tell if this is going to work for you.
>
> I use them on my boat for hitting shore based APs. Since the boat is
> constantly swinging at anchor an omni antenna is absolutely essential,
> and the higher the gain the better. I have sometimes been able to
> connect with good outdoor APs that were over 4 miles away.
>
> This is the one I'm using at the moment:
>
> http://wlanparts.com/product/GP-24-3
>
> High gain omnis are also useful at APs where wide outdoor coverage is
> needed.

--
..

Here is the one I bought and it works great for me:
http://wlanparts.com/product/O2415


I would like to buy the commet you mentioned though.




Wayne.B <(E-Mail Removed)> wrote:
> On Mon, 16 Jul 2007 01:34:13 -0700, Jeff Liebermann <(E-Mail Removed)>
> wrote:
>
> >I don't think my previous comments sunk in. So, I'll be blunt. High
> >gain vertical omni antennas are awful for just about all but a few
> >specific applications. You haven't bothered to specify yours, so I
> >can't tell if this is going to work for you.
>
> I use them on my boat for hitting shore based APs. Since the boat is
> constantly swinging at anchor an omni antenna is absolutely essential,
> and the higher the gain the better. I have sometimes been able to
> connect with good outdoor APs that were over 4 miles away.
>
> This is the one I'm using at the moment:
>
> http://wlanparts.com/product/GP-24-3
>
> High gain omnis are also useful at APs where wide outdoor coverage is
> needed.

--
..

"Wayne.B" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Mon, 16 Jul 2007 01:34:13 -0700, Jeff Liebermann <(E-Mail Removed)>
> wrote:
>
>>I don't think my previous comments sunk in. So, I'll be blunt. High
>>gain vertical omni antennas are awful for just about all but a few
>>specific applications. You haven't bothered to specify yours, so I
>>can't tell if this is going to work for you.
>
> I use them on my boat for hitting shore based APs. Since the boat is
> constantly swinging at anchor an omni antenna is absolutely essential,
> and the higher the gain the better. I have sometimes been able to
> connect with good outdoor APs that were over 4 miles away.
>
> This is the one I'm using at the moment:
>
> http://wlanparts.com/product/GP-24-3
>
> High gain omnis are also useful at APs where wide outdoor coverage is
> needed.

* I'm glad the antenna of such as gain has worked well for you. I would
think that it would be possible (see beamwidth earlier by Jeff) to miss some
access points or hotspots altogether because you either over or under shoot
them on transmit and receive. I think 8.5dBi is about average recommended
especially for marine.

---
Alan Spicer
DBA Alan Spicer Telcom / Alan Spicer Marine Telecom
Computer Services, Wired/Wireless Networking,
Cell/Sat/Landline Communications, General Consulting...
Marine, Business, Small Office and Home Office (SOHO)
* http://telecom.dyndns.biz/ (Main Site)
* http://www.marinetelecom.net/ (.net mirror site)
* http://alanspicermarinetelecom.com/ (.com mirror site)
* http://www.wifiyacht.net/ (Yacht WiFi Main Site)
* http://www.mymarinewifi.com/ (Marine WiFi .com mirror site)