"Norm Mann" wrote in message
news:HDV1g.10938$oQ2.4421@trnddc05...

wrote in message
ups.com...
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.

A coax stub filter to notch out the pager would probably work better.
It's cheap to make, but it also has some drawbacks - signals within
roughly +/- 10 MHz of the notch may have as much as 10 dB of attenuation.
Your friend may be able to cope with some attenuation better than 100%
overload.

-NM


You will not meet your goals with a real world LPF. A coaxial Stub may
yield -20dB attenuation but have terrible in band (2M) VSWR and high loss.
The previous poster is correct- a notch- particularly an asymmetrcial notch
is the proper solution.

50dB or greater attenuation at 163 MHz with in band loss of under -0.4dB is
easily achieved. See:
http://www.eham.net/reviews/detail/3716

Or:
http://www.eham.net/reviews/detail/385

Dale W4OP