John Navas <spamfilter0@navasgroup.com> hath wroth:

>On Sat, 11 Nov 2006 21:24:41 -0800, Jeff Liebermann
><jeffl@comix.santa-cruz.ca.us> wrote in
><lrbdl2h6ibsprfobs9af163mjp8o3enve4@4ax.com>:
>
>>miso@sushi.com hath wroth:
>>
>>>Fry's has an Airlink 10dbi directional antenna on sale, today only. OK,
>>>you have about two hours. $9
>>
>>I think it's this one:
>> http://shop2.outpost.com/product/4901671

>That's an omni.

Oops. Sloppy cut-n-paste.
http://shop2.outpost.com/product/4901691


>$17 here:
>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130045666269>

>>>I bought the Airlink omni (9dbi I think) and it wasn't even close to my
>>>home brew biquad. Worse yet, it didn't perform as well as the antenna
>>>in my SMC card.

Omnis have a much narrower beamwidth than a directional antenna with
the same gain. For example, a 10dBi vertical omni will have a
vertical -3dB beamwidth of about 30 degress. A typical 11dBi biquad
will have a vertical beamwidth of about 50 degrees:
| http://802.11junk.com/jeffl/antennas/Biquad/index.html
That makes the antenna position and orientation less critical with the
biquad. The omni also has many more reflections and multipath
problems than the directional antenna. If you compared antennas in a
typical cluttered environment, the reflections will have a big effect
on link reliability.

>The 10 dB directional antenna is
><http://www.airlink101.com/products/asb-10da.html>

Chuckle. Look at the numbers. One line says:
Antenna Type 2.4GHz 8dBi Indoor Patch Antenna
while another line says:
Gain +10dBi
So, is it 8dBi or 10dBi gain? Maybe they really did include the coax
loss, and then changed their mind.

My guess(tm) is that there's more coax cable loss on the Airlink
antenna than your home made biquad. At least you probably used fatter
and better coax. The data sheet doesn't specify the coax length but
I'll guess about 2m of RG-316/u coax. That's about -2.4db loss for
the pigtail. That's a bit less than half your power lost in the coax.
Instead of a 10dBi antenna, you have a 7.6dBi gain antenna. Specifying
the antenna gain and ignoring the coax loss is in my never humble
opinion borderline fraudulent advertising.

--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558