Spent some views on the Warbler's design again, and came to the conclusion that a single crystal in the either TX and RX filter would probably be OK for WSPR and AFSK-QRSS.
For RX, three crystals are foreseen, assume, we would be using one only, one xtal location could be shorted and the other unused one could be populated by a capacitive trimmer, for tuning the filter's response.
For TX, two crystals are foreseen, however, I believe a single one would do for sideband rejection... w/o any further periphery actually.
Reasons: multi-pole filters are employed to widen the filter's response... at a bandwidth of 200Hz (WSPR) of 300Hz (QRSS+WSPR) there is no reason to bother with widened bandwidth, that's what a single xtal has proven to be able in my sub-harmonic DC-RX already.
