On Sun, 14 Apr 2013 13:01:15 -0700, "garyr" wrote:

I'm trying to build a 80/40 meter receiver and I'd like to be able to
switch the RF input between the two bandpass filters. This sort of thing is
usually done with relays but I'd like to avoid that if possible. A
SN74CBT3306 would be ideal but I think the on-resistance would be too high,
thought it's hard to tell from the data sheet. Are there other devices that
would be suitable for this application? What do you think about using
2N7000's for this job?

The input and output capacitors of the double-tuned filters are 2200 & 2700
pF so the stray capacitance of the switching circuitry would not affect the
response very much.

Thanks in advance

In receivers like for instance those of ICOM (R71 etc.) and Kenwood (R1000
etc.), the input and IF bandpass filters were switched with diodes (N4148 or
equivalent). With a current of ~10 mA through a diode this works rather well,
regarding both IM and loss. But because at that time circuits weren't
simulated, it was overlooked that due to the diode capacitance, filters supposed
to be switched out, still exerted (often a nasty) influence. To eliminate that,
you'll also have to use a diode switch as a short circuit for the filter not in
use.

Jan