John B. Stephensen wrote:
Since the noise is always symmetrical around the received signal, the switcher noise must be modulating the VCO control voltages. There are two switchers - one on the receiver PCB and one on the CAN-DO module. We must determine which is causing the problem or whether both are. Can you cut the trace on the PCB and vary the DC voltage to the receiver independently of the voltage to the CAN-Do module?
I agree with this switcher comment and did as soon as I saw the picture. I really hope this is not the CAN-DO module as FLIGHT UNITS have been DELIVERED for P3E. We need to have Stephen, et. al. check the noise output of the switcher on the Can-Do module.
I hope that you can tap each component and find the microphionic one. Good candidates for microphonic components are the capacitors in the PLL feedback loop. The capacitors in the integrator are film types so they shouldn't be microphonic but perhaps SMT parts aren't as good as leaded parts. The ceramic capactors in the feedback path might also cause problems and could be changed to film capacitors. Another possibility may be the 4.7 and 10 uF bypass capacitors on the outputs of the linear regulators. These are ceramic because of concerns about tantalums in space but they might have good piezoelectric properties and could be switched to 1206 size tantalum capacitors. There could also be a cold solder joint somewhere.
73,
John KD6OZH