On 8-Feb-2004, Don Tuite wrote:

Hey Jim. How about an antenna-line pad (maybe 40 dB or so) that you
could switch in when listening to union? The local guys would still
break squelch, but the guys 100 miles away wouldn't.


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. 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.

It's an imaginative idea, though.

-Elliott Drucker