Posted by
Mike Scott-7 on
Mar 12, 2006; 12:22am
URL: http://elecraft.85.s1.nabble.com/KX1-signals-peak-at-low-audio-beat-frequency-tp387498.html
First post to this list
The KX1 has a fixed BFO designed for 600Hz offset; this is where I expected
signal audio to peak. I validated what I thought I was experiencing that
signal audio peaks closer to 400 Hz than 600 Hz, lower than expected.
I put an audio spectrogram on the audio out of my KX1 (Visualization
Software PC version). Input to KX1 was the XG2 signal generator at 7.040
MHz. I set up so that I was showing a good S/N and then manually swept the
end-to-end response of the entire RF-to-audio path by slowly tuning the
receiver across the signal plotting response peaks.
End-to-end response shape seems normal falling off 20 dB per octave far
above the peak and rising faster far below the peak with a nice rounded peak
that is obviously sharper at the lower filter settings.
Results tabulated as follows picks off the peak and -6dB points of the end
to-end-response for four different filter settings:
Filter setting Peak Audio -6dB High -6dB Low
Maximum 592 Hz 1214 Hz 159 Hz
1.0 500 Hz 697 Hz 259 Hz
0.5 442 Hz 554 Hz 321 Hz
Min 444 Hz 516 Hz 337 Hz
As you can see with narrower filter settings the maximum signal tune point
is a beat-frequency tone just north of 440 Hz. The signal is already more
than 6 dB down by the time I have tuned to the design 600 Hz offset point,
where I would zero beat another signal.
Have other KX1 owners noted signals peaking at a low CW tone? I find myself
listening to some low notes on weak signals and this means I do a rather
poor job of zero beating.
I don't have an RF frequency measurement tool but am suspecting that the BFO
could be set more optimally in my case.
Does anyone know if there is a way that I might trim the BFO frequency
100-200 Hz lower? Or, possibly there is something else going on and I am
looking in the wrong place?
Mike Scott
AE6WA
Tarzana, CA
DM04
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