Cathy:
A trick I've used in the past with RTTY demods is to drive the demod
audio input (or sound card) via a step-up audio transformer.
In the days of tube-type demods, I would connect a tube-type audio
output transformer backwards across the receiver speaker output, but
that would produce too much voltage for a sound card. However, a
transistor audio output transformer should be about right, something in
the 8 ohm : 200 ohm range.
Of course, you could do the same type of voltage amplification with an
op amp, but a transformer works well for this application.
Or, you could use the microphone audio input instead of the line input.
Plenty more gain there, and most computers have an auxiliary +20 dB gain
switch.
Jack K8ZOA
Cathy James wrote:
I ran some tests this evening with my K2 and my computer sound card
and HamScope software. 80 meters was not great, but it was open and
there were a number of QSOs going on.
The K2 was able to pick up signals and decode them quite well, and the
narrow filters really help block QRM. (My RTTY filter bandpasses are
all over the place, though; I don't think I ever finished setting them
up after getting Spectrogram going. Have to revisit that!)
However, the audio drive from the K2 is much less than from the
DX-70TH that I use as my primary digital mode rig. Although the
signals decoded well, the traces on the waterfall barely showed even
at fairly high soundcard record volume settings. With the DX-70TH
plugged into the sound card instead, the same signals were brilliant
yellow and easily found by eye.
What can I do to increase the audio output level of the K2 for sound
card purposes?
Cathy
N5WVR
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