Converting the W4IMP Transmitter into a Transceiver configuration. Well indeed, who am I to go messing with the superb work done by W4IMP? Bottom line, it is just a terrible affliction of looking at a circuit and seeing possibilities.
W4IMP is specific in his article that this 15M rig is just a steppingstone to an all-band rig he has in the works. So, he too has the affliction.
In 1961 I was halfway through a BSEE, and I doubt I could have designed his original work. But having built so many SSB rigs some 60 years later you get a feel of topologies and what can be done with many years of data stashed on the Internet.
A word here about my rig fabrication process that involves upfront noodling and simulation. My soldering iron is off and will be off until I have looked at a literature search.
This is not the complete block diagram but shows how to diode steer the Audio Amp/Mic Amps, the New Crystal Filter and the two RF amplifiers such that one is the Receiver RF Amp, and another is the Transmitter Pre-Driver.
A good stop and smell the roses point is the 50 Ohm input output impedance matching. Consider that the HB Filter likely has a Z in/out in the 200 Ohm range so you will need some 4:1 matching.
The LT Spice simulation below show the RF amp circuits. About 10dB gain at 21 MHz with 500 mv of input which certainly would be the case for the transmit side. Yesterday's post had the Audio Pre-amp and Mic Amp circuits.
Essentially, you build two Diode Ring Mixers, a Crystal Filter, and 4 amplifier blocks -- two at audio and two at RF. The Driver Stage could be a 2N2905 and the Final Amp a 2SC1969. [The 2N2905 is the PNP equivalent of my go to 2N2219A.]
RF Amp Simulation
The Audio Amp/Mic Amp Simulation
The Key take away is that with some simple circuitry you have the beginnings of an SSB Transceiver.
Lest I forget -- the two HB Double Balanced Mixers circuits.
Start scouring the junk box and just think an unconventional use of PNP transistors.
If you use a 9 MHz IF, then a simple 5 MHz Analog VFO would get you on 20 Meters. That VFO frequency would be a lot more stable than an LC 13MHz VFO. I only mention the analog VFO for those averse to Arduino's and Si5351's. We have a big tent.
Keep noodling.
73's
Pete N6QW