[eagle] Re: New 70 cm Receiver Test Results

Robert McGwier 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.
> 73,
> John

AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
"If you're going to be crazy, you have to get paid for it or
else you're going to be locked up." Hunter S. Thompson

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