[eagle] Re: New 70 cm Receiver Test Results
rwmcgwier at gmail.com
Sat Jun 9 07:03:47 PDT 2007
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.
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