RadioBanter - View Single Post - HB VHF low-pass filter

April 21st 06, 12:43 AM posted to rec.radio.amateur.homebrew

wrote:

Hi gang,

And old chum of mine suffers badly from pager interference when he's
trying to listen on the 2m band. The interference is strong to him
(S9+) and takes out all his reception, despite the fact that it's quite
a way up-band at 153Mhz.
I've been looking into designing a filter for him to cut off by 153Mhz
to better than -20db but it turns out to be rather more tricky than I'd
imagined. Even with a seven element butterworth configuration, the
difference between the 146Mhz (wanted) and the 153Mhz (unwanted is an
insignificant 6db or so. I'm just not getting enough roll-off and need
something much sharper. Worse still, the roll-off I'm seeing is on a
computer simulation of the filter with ideal components and would no
doubt be even worse with real-world Ls and Cs. Any suggestions as to
how to tackle the problem, guys?
Thanks,
P.

If its just one transmitter he would be better off with a notch
filter.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida