Omnidirectional Antennas

Marty Galyean marty
Fri Apr 2 09:05:49 PST 2004

Kelly nailed it, the higher the db of the omni, the flatter the toroid
of tx/rx.  On a related note, on sailboats people often mount high db
antennas to reach farther but the pitch and yaw of the boat in the waves
causes the signal to blink in and out as the narrower "squished donut"
plane of reception/transmission swings above and below the distant
contact more easily.  For this reason many boat owners keep their omnis
to 6db or so, to get the larger vertical angle at the cost of distance. 
Some have both so they can use the higher db in calmer seas.

Many howtos on the web say to mount "as high as possible" but they are
simply wrong.


On Sat, 2004-03-27 at 19:09, Kelly Hogan wrote:
> Dave,
> How high are you placing your 15db omni?  How long is your coax, and
> what type?
> A common mis-conception is that omni's have deep vertical transmission 
> patterns.  We have found that the higher the gain of omni, the thinner
> the doughnut of pattern around the antenna.  A lot of people place these
> high gain antennas way up high, expecting good coverage, then only find 
> that they are putting the sweet spot over their targeted areas.
> Try lowering your antenna, or get its plot of coverage and do some 
> good ol trig math to determine its best coverage area.  Then of course
> trial & error is good as well. 
> We use a similar setup and get nearly 6-700m of good coverage.
> Best
> KH
> > Right now I am currently using a 15dBi omnidirectional antenna with 
> > Host-AP on redhat 9 with a senao nl-2511 CD Plus EXT2.  I like the 
> > setup as far as the card and server go, but with the antenna I haven't 
> > been really impressed with it so far.  As of right now I'm getting 
> > about 150m when I should be getting at least 300m.  Has anyone found a 
> > good omnidir antenna for a decent price?
> > I am getting ready to start my second hot-spot, am looking for a decent 
> > antenna, with the same setup of card and server.
> > 
> > Dave
> > 
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> >
> > 
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