I think there are TWO incompatible applications being discussed:

1) The original request was for narrowband BPF for portable operating

on a mountain top in the presence of commercial transmitters.

Usually needs a relatively large cavity or heloical resonator. This is

for the annual APpalachian Trail GOlden Packet event 17 July

http://aprs.org/at-golden-packet.html

2) The more common AMSAT need for a LPF to prevent front end

overload of the third harmonic of a VHF upllink into the UHF receiver.

The solutions are very different. - Bob, WB4APR

On Thu, Jun 10, 2021 at 2:08 PM Joseph B. Fitzgerald <jfitzgerald@alum.wpi.edu> wrote:

Mini-circuits has sub $100 filters available suitable for receiving applications:

https://www.minicircuits.com/WebStore/RF-Filters.html

Meeting the 0.5 dB insertion loss specification might be difficult though.

-Joe KM1P

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