re: [BAWUG] Single Antenna - Multiple Radios

[Jim Aspinwall]

Eden:

At the risk of alienating about half the list...

Your power divider just ate 4-6 db of signal per port. Good non-overlap plan but you're still feeding a 'lot' of power back into the other receiver. Without adequate band-pass or band-reject filtering no sane RF engineer would ever do this in ham or commercial practice.

You also have NO protection against intermodulation and mixes between these devices and will create a lot of out-of-band signals that can potentially mess up other services. If you're doing this at a commercial site, or near one, and a site engineer or adversely affected party catches and finds this - be careful you don't find the gear crumpled in a heap someplace - no worries about the FCC - there won't be any gear left to fine you for.

(Recommend you take lots of replacement coax, connectors and power cords with every site visit...cutting same into 6" pieces and stacking them near your equipment is a popular deterant among those wronged by inteference.)

Not to mention that this is definitely a non-certified system implementation...

We know this is fun, especially to test the limits and craft better than intended performance, etc., and I applaude the creativity and tenacity, but these practices are not unlike the rampant CB 'kickers' and other gizmos that gave Channel 19 such a bad name.

At least the CBers were playing in their own sandbox except for the occassional "good buddy" crap that hit the neighbor's stereo or TV. In this case 802.11 is VERY definitely in a lot of OTHER (licensed or primary) people's sandbox as a 3rd-class citizen as far as rights and tolerances - you don't have ANY, especially if this style of creative "ad-hoc engineering" continues.

What you have created is an unsound and potentially 'harmful' RF 'system' that would never pass a certification under any circumstances. Toss enough of those together and you're creating an RF nightmare - if not for yourself, others.

I'm sure I echo the sentiments of more than a few licensed service users and potentially affected victims of such creations. If you get away with it, consider yourself lucky, and ONLY lucky. There are proper ways to do this stuff, and this is not it.

As far as masts, mounts, etc. IF you're not dealing with a stout thick-wall piece of properly guyed 1.5 - 2" steel pipe you're probably headed for mechanical failure. The windload of a single antenna or two is not bad, but a 'lot' of them suddenly increase the surface contact area for the wind to start turning the antenna system into a large pretzel - no mustard or salt. I do a LOT of high-steel work and have seen some of even the best commercial hardware installations turn to scrap in a high wind.

"Message: 12
Reply-To: <[EMAIL PROTECTED]>
From: "Eden Akhavi" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Date: Fri, 8 Nov 2002 02:03:42 +0100
Organization: LTT Inc
Subject: [BAWUG] Single Antenna - Multiple Radios
Following on from the questions I asked a week back - I have done some
basic testing today connecting two radios to a single antenna. The
primary objective was to enable us to increase the number of channels
available on a sector antenna rather than deploying a second antenna.
I used Huber & Suhner 3 way Power Divider, connected an AP2000 with two
radios (1 on channel 1, the other on channel 10) - the antenna used was
an H&S 85 degree sector antenna. It appeared to perform flawlessly - the
number of errors did not increase on either of the radios, neither did
the signal or noise level change.

I'll do some proper testing over the coming days and if anyone is
interested I will post the results. Our biggest headache is increasing
the number of antennas on a mast, if we can make this work properly it
will allow us to increase the number of clients on a single antenna by
spreading them over different channels.

If anyone else has tried this please let me know - I'd like to compare
notes."




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Jim Aspinwall - [EMAIL PROTECTED]
"lack of (the right) information is a dangerous thing"
B.A.R.F. UHF Repeater - 443.750 - San Jose PL 100 - Vaca PL 127.3
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