OK. got access to the spreadsheet. Setting the stub+short+connector loss
to 0.25 dB, and cutting the stub for 55.25 gives about 15 dB loss at 50 MHz,
and about 30 dB loss at 55.25. This probably is good enough to either
prove or disprove the hypothesis about what is causing the problem (video
carrier overloading the RF amp), and an inexpensive way to find out.

As a long-term solution, a bandpass filter would be easier provided it had
loss low and SWR (so it could be left in-line for transmitting).

-- Tom




"Dale Parfitt" wrote in message
news:jZAjd.2538$bH2.1351@trnddc09...

"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find
some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is
difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP