[SunRescue] Suburban Wireless?

[Chris Byrne]

James Sharp wrote:

>> Some acces points advertise up to 250 meter range, but with the standard
>> antennae you are lucky to get 100 meters,and more like 50 with
obstructions.
>> It's illegal to amplify the signal beyond a certain point, where it could
>> "cause undue interference" which basically means scrambling your
neighbors
>> cordless phones etc... etc... so your best bet here is good antennae
design.
>
>They're certified under FCC part 15, which means a) It cannot cause
>interference and b) Must accept any interference.  But yes, good antenna
>design is definitely a must.  You can overcome a lot of the problems
>caused by lack of transmitter/receiver horsepower with antenna gain.

I always wondered why they included the "must accept any interference" part.
The language is such that if for example I used braided coaxial shield on my
feed line then I would not be accepting interference. I always thought it
was kind of pointless.


>Unless you're going to put the access point within a few feet of the
>antenna, you'll need to end up using some rather expensive hardline to
>make the run.  Even good quality Belden 9913 has atrocious loss at 2.4Ghz.

I'm sure it does. I've never done anything in the way of amateur radio with
gigherz stuff so I've never figured it. Anyway that's why I suggested a
short run in the next section.

When I did this in a business environment we had something like a 1 foot
feed line going into a powerhorn that had been specifically designed for 2.4
ghz. The line was semirigid coax, and I believe it was teflon dielectric
with a braided copper or aluminum shield but I'm not 100% sure since I didnt
wire it.

>Use the yagi at the remote node sides, and then use a coaxial collinear
>antenna at the central point...they provide excellent omnidirectional
>gain.

That would assume you had a star pattern network with centralized routing.
It would certainly be more efficient from a comms standpoint, but it may not
be physically practical.

>Adding circular polarization would only make building decent omni-antennas
>difficult at best...and really wouldn't gain you anything.

I'd agree with you on the difficulty of making an omnidirectional circularly
polarized antennae.

>CP really only gains you anything (IMHO) when you shoot through the
ionosphere and have
>to deal with Faraday Rotation.

That one I'm going to disagree with you on. I have seen radiation studies on
various types of antennae for MDT (mobile data terminal) setups for Police
and Utility company use. They clearly indicated that circular polarization
reduced attenuation caused by soft obstructions (houses, trees, cars,
basically anything not a part of the earth or huge and metallic), but that
was in the public safety bands, which are all considerably lower frequency
than 802.11b equipment.

Chris Byrne





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