[eagle] Re: New 70 cm Receiver Test Results
juan-rivera at sbcglobal.net
Sun Jun 10 07:51:35 PDT 2007
Thank you. That's a good idea and saves one power supply. I'll go with the
battery and ten-turn pot method.
From: eagle-bounces at amsat.org [mailto:eagle-bounces at amsat.org] On Behalf Of
Sent: Sunday, June 10, 2007 12:42 AM
Cc: 'Dave Black (Home)'; 'David Smith'; eagle at amsat.org; 'Dave Black (Work)'
Subject: [eagle] Re: New 70 cm Receiver Test Results
The VCO control line will be extreemly sensitive to noise; testing VCOs
with a power supply often gives more data about the power supply noise
than the VCO performance. If you want to open the loop and control the
VCO directly, I would suggest controlling the VCO using a battery with a
potentiometer (10 turn if possible, or 'padded down' with resistors to
give a reduced VCO control range) and maybe a large value parallel
capacitor or two.
Juan Rivera wrote:
> I'll tackle that tomorrow. For this prototype we can actually do
> exactly what you suggest and just move the PCB back one set of standoffs
> and leave the Can-Do module where it is. Of course the SMA connectors
> will be inaccessible with the cover on but I don't run it that way when
> testing anyway, so it won't matter.
> Getting the Can-do module desoldered won't be much fun but it should be
> possible. That's a job for next week. I think I'll find tomorrow that
> U17 is also a contributor to the noise. Perhaps I should cut into the
> VCO control loop and control the VCO with an external supply if it
> starts to look like a culprit. Right now I'm out of variable supplies
> since all three are tied up. I don't have an oscilloscope that I trust
> but I may be able to use the SDR-IQ with a scope probe to look at the
> VCO control loop since it goes down to 500 Hz. That will be an
> interesting test. This little radio is very useful.
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