>RE: 2m Bandpass Filter Reply
by N8EKT on February 19, 2009 Mail this to a friend!
Make your own 1/4 wave stub filter.
There are many online 1/4 wave stub calculators available and all you need is a length of coax and a "T" connector.
One stub cut for 152 mhz should eliminate the paging signals.<
::That idea is right, but in practice I think you'll find it's impossible to do with ordinary coax, because you can't achieve a high enough Q to get reasonable rejection with a frequency spacing of only 6 MHz at 150 MHz.
Q = fc/BW if I recall...
Q required at 146 MHz for a BW of, say, 4 MHz would be 36.5. A 1/4-wave stub (open ended) cut for 152 MHz having such a high Q would need to be made of awfully good, extremely low resistance coax. Maybe 7/8" hardline could do it, but I don't think one could get there with RG58/U.
PAR ELECTRONICS makes an excellent in-line 152 MHz trap filter for this application. It has BNC connectors already on it and can handle a bit of transmitter power. I've used theirs for years, they do an amazing job. Not expensive at all.
WB2WIK/6