Once the harmonics and spur issues are put to bed, what will remain is unacceptable levels of intermodulation distortion produced by the Termination Insensitive Amplifiers used as bi-directional IF amps at both 45 and 12 MHz.
This is a prototype MMIC amplifier utilizing the ERA-3SM+ (80 cents each on eBay) mounted on an RF prototyping board ($2.50 each from SV1AFN) that is the proper size and form factor to replace both transmit TIAs. The MMIC/board measure flat response from 300 Hz to well over 200 MHz.
This test quantifies the IMD performance of the combo. The reference point on the SA is shifted +6 dB so that the readings reflect the power level that would be achieved with a single tone for convenience of interpretation.
Measurements were taken at Vcc of 3.3 volts and current draw was the recommended 35 ma.
The blue trace shows performance at 0 dBm out and is an acceptable -42 dBc (-36 dB minus 6 dB for a single tone carrier). Performance at - 10 dBm out, the level needed to drive the uBitx driver/PA chain, is an excellent -51 dBc (-45 dB minus 6 dB for a single tone carrier).
Yet to be determined is how to add the LM1117-3.3 regulator to hold the Vcc at the required level.