On Tue, 10 Feb 2004 03:59:00 GMT, wrote:

Well, I'm not Jim, but what the hey, it's a public forum.

Like you, I am often frustrated by congestion on unicom frequencies in and
around urban areas, BUT...

Unfortunately, the difference in received signal level from equal power
transmitters 10 miles away and 100 miles away is only 20 dB (assuming
line-of-sight). There is probably 10 dB variability in effective unicom
station transmit power owing to different antenna gains, cable losses, etc.
That leaves only a 10 dB "window" to separate "desired" signals from
"undesired" ones, and only about 4 dB if the undesired is a more realistic
50 miles away.

It'd be worth an experiment if you could get the hardware.

An additional negative would be the two coax relays or other
type of RF switches required to switch the pad in and out. These would add
considerable cost and reduce reliability, but most significantly would hurt
receiver sensitivity (since there will be some signal loss in the switches.

I was hoping one could find old Transco "D" switches on the surplus
market. (I worked for Transco in the early '70s.) At VHF and UHF,
they had exceptionally low insertion loss and VSWR and exceptionally
high isolation in a small form factor. Generally, the conectors were
SMA.

Maybe that's a pipe dream.

Don