Posted by
w8fn on
Sep 27, 2009; 8:33pm
URL: http://elecraft.85.s1.nabble.com/K3-FSK-power-transients-tp3712691p3722808.html
>I experience the same issue and Elecraft indicated that the FSK mark/space
>power fluctuations are caused by the transmit filter's passband ripple and
>where the transmit signal falls within the filter's passband. I'm using the
>standard 5 pole 2.7khz filter. They indicated the 8 pole filter should be
>flatter.
I'm using a 2.8kHz 8-pole as the main transmit filter and at nominal
100W output I can see a perceptible "wobble" on the wattmeter as the
signal shifts between mark and space. It's hard to believe the
ripples in the filter would be so steep that a 170 Hz difference in
frequency of the two tones would make much difference. If you use the
standard 2125 Hz / 2295 Hz mark/space convention, this would make the
signal appear fairly close to the filter's transition band, assuming
there's no center frequency offset applied in the transmit path. This
amplitude mismatch will introduce an unintentional AM at the baud
rate, but it's probably not enough to appreciably broaden the
transmitted signal. I don't have access to a spectrum analyzer or I
would examine this further. Maybe someone with a well-instrumented
bench can have a look and report back.
73...
Randy, W8FN
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