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"Sal M. Onella" wrote in message
...

Open quarter wave, shorted half wave. I don't know which is better.
Remember to shorten the stub length by the velocity factor of the coax.

snip

I bought a "Midband Trap" from a TV
shop downtown which fixed things. It went inline and attenuated those
non-TV signals between (approx) 120 - 170 MHz.

I have good and bad news to add:

Last night I built some stubs with TV coax and BNC T-connectors. I swept
them with a spec-an/tracking-generator. I could produce a nice 2m notch
with one stub and (by careful trimming) a nice bandstop filter with two
stubs, separated by an intermediate length of cable. There was some ripple
in the passband, probably due to impedance discontinuities. That's the good
news.

The bad news is that there was also loss at freqs for UHF channels 14, 15 &
16, as well as Channels 45 and up. (If your building had separate antennas
for VHF and UHF, this effect could probably be avoided. You trap the VHF
antenna cable, then join the separate U/V antennas at the amp input. Maybe
the amp has provision for separate VHF & UHF antenna inputs. Many do.)

Back to good news: My junkbox contained a midband trap, a Winegard BRF-170
which I put in line and found it to be near-perfect. Stopband between 120
and 160 (about 25 dB) with minimal effect on the passband.

Bad news, http://winegard.com/offair/traps.htm doesn't show the product.
I'm still looking.

Good news: I also have a highpass filter, a Pico TTHPF02M. It attenuates
everything below 50 MHz, good for what you said might be a 10m EMI problem.
I've found recent references to it in other NGs, but no sign of a vendor for
exactly that item. News is still OK, as a "filter" search of the Picomacom
website switched me directly to a Yahoo purchase website, where they offer a
similar product http://yhst-18278607509093.stores.ya...pico-0145.html.
TV highpass filters with cutoff around 50 MHz are fairly common. For a few
bucks, try one if you confirm a 10m problem.

I hope this helps.

"Sal"
(KD6VKW)