John,
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.
73,
Juan
From: John B.
Stephensen [mailto:kd6ozh@comcast.net]
Sent: Saturday, June 09, 2007 8:08
PM
To:
Cc: eagle@amsat.org;
Subject: Re: [eagle] Re: New 70 cm
Receiver Test Results
Reconnect the switcher on the receiver PCB and see what
shows up.
To eliminate the noise, we may have to connect the PCB
to the CAN-Do widget with a ribbon cable and place it at the other end of
the module case. If the internal switcher also pollutes the VCO control
voltage, it could be moved to a separate PCB.
73,
John
KD6OZH