My general impression is that ladder filter terminating impedances tend to
be based on the general frequency range of the crystals.

I built some 5.000 MHz ladder filters that work best with 270 ohms
termination, while a filter I read about in an article which was at 12 MHz
had 50 ohm impedances.

Of course, one can work with either termination....

In my case, I had calculated that 5.000 MHz IF and 1.2 MHz VCO would
result in a 7 MHz transciever with VERY few mixing spurs anywhere near a
frequency that would bother my design.

So, in general, I think the frequency of a ladder filter can be low or
high, and used for either SSB or CW. But, mixing spurs and so on should be
considered when choosing an IF.


Jim Pennell
N6BIU