In the development of the original 40M Wireless, I purposefully used two separate Band Pass Filters. The original Swan 120, which was the template for the wireless it had tuned coils. I converted that part of the design to broad band with the BPF ahead of the 12BA6 RF amplifier stage
Another innovation was the use of a homebrew 2.5 mHy ferrite core choke in the plate circuit of the 12BE6 transmit mixer where a couple of turns of wire on the FT-82-43 core provided a 50 Ohm tap point. From this tap point the transmitted signal passes through a second Band Pass Filter and on up the RF transmit chain.
A simple mod to the 40M Hybrid Wireless gave proof of life that receive on 20M was quite good. Two more changes are needed to prove 20M transmit and these include a 20M transmit BPF and the 20M LPF following the genuine IRF510's (from Jameco... no BoJack's here.)
This design uses 9-50pF Trimmer caps available from Jameco Electronics. If you parallel a 150pF cap with C1 and C2 and replace C4 with a 5pF Trimmer cap this can be tuned to 40M. Note R1 is for the simulation and not installed as hardware.
20M BPF
Our LT Spice simulation reveals a nice flat response across the SSB Phone band and so this design should do well in the 20M Hybrid.
Using an existing stored CNC program about 5 minutes of work created two PC boards for the new BPF's. That is on the agenda for today's work.
Hide your digital footprint as we are all being watched.
Them that know can make things go.
73's
Pete N6QW