Tom Thompson wrote:
Kurt,
Sound cards are just begging for RF interference. They have high
impedance inputs and high gain, and as a result, they are subject to
fundamental overload. I have used F114-77 toroid cores from
http://palomar-engineers.com extensively on my Delta 44 leads and
computer leads with good results. Wrap as many turns as you can of each
lead close to the card and the SDR-1000 using two toroids.
Good luck and 73,
Tom W0IVJ
Kurt Vangsness wrote:
I'm finally starting to play around a little bit with CW and in
preparation I'm trying things out with my radio putting < 1 watt out
into a dummy load (I have an external amp which is off for these tests)
and am monitoring my transmission from another receiver. I'm noticing
that my transmitted CW tone is not steady - almost as though the
transmitted frequency is wavering. I don't notice this with other CW
signals received on the radio I'm using to monitor so I have to assume
it is my transmitted signal... The resulting effect is almost like a CW
transmitter with a very unstable LO.
I tried an experiment monitoring the LO from the sdr-1000 (while the
sdr-1000 was in receive) from the same receiver and it does not exhibit
the same variations in tone.
One (possibly unrelated) thing I've noticed on my sdr-1000 is that I
appear to be getting fairly strong interference from a local AM station
on the sound card input. In the panadaptor display I can see the carrier
at the bottom of the display (when tuned to the lowest frequency before
the radio retunes the DDS). With my radio connected to a dummy load
(noise floor is down at the bottom of the display), the carrier shows up
around -85 dBm! I've made a wave capture of the I&Q and tuned to the
carrier and verified that it is a local AM station. I'm wondering if it
is possible for a strong signal like this on my audio cables to somehow
cause the tone/frequency changes I'm observing on my transmitted CW
signal. Any ideas (both on the CW instability and in getting rid of the
AM signal on the sound card)?
73 and Happy Holidays,
Kurt KC9FOL
Configuration details: P4 2.4 Ghz, 1GB RAM, Delta 44.
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