July 8th 03, 05:32 AM
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In article ,
says...
i see a lot of transmitter schems where the VFO's power is switched with
the mic or key. and i saw a test where it took 5 minutes of warm up time
for a VFO to stabilize.
Mike-
One of the effects of keying the VFO by keying the power, is a distinct chirp.
Another method used in the vacuum tube days, is grid-block keying. A negative
voltage is applied to the grid of the oscillator tube, and shorted to ground to
turn on the oscillator. This approach would apply to an FET oscillator as
well.
Keeping the oscillator running and keying subsequent stages will usually
produce a more stable signal. However, it is not unusual for some of the
oscillator's signal to leak through and be radiated by the antenna. You can
probably imagine a CW tone that gets louder when keyed, but the pitch doesn't
change. When such a station is nearby, it is hard to discriminate between the
strength of the keyed and unkeyed signal. If you use this approach, you should
pay attention to keeping the oscillator from bleeding through. One method
might be to key all of the following stages, for example.
that's what i was thinking. key the amps and maybe dump the VFO into a
terminator inside the RFI shield thru a good pin diode switch.
mike
73, Fred, K4DII
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