Posted by
Ron D'Eau Claire-2 on
Aug 31, 2006; 8:33pm
URL: http://elecraft.85.s1.nabble.com/KX1-improvements-tp393532p393543.html
Vic, K2VCO wrote:
Geoff is talking about keying a flip-flop which is between the LO and
the mixer. It can be used to gate the LO signal (as well as to convert
the mixer signal to the 50% duty cycle square wave required for the type
of mixer that he recommends). He's not recommending keying the LO itself.
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It doesn't matter where in the path you switch the signal, turning it on and
off causes sidebands. Actually it causes mixing which produces sidebands -
sum and difference frequencies based on the modulation frequency (the rate
at which it's turned on and off) and the signal being switched.
Does putting the switch in the L.O. path avoid those? I wonder. The act of
switching the L.O. on and off means we're feeding three fundamental
frequencies into the mixer in the signal path instead of two, plus the
sidebands from switching the L.O. on and off. It sounds to me like we'll get
a huge range of additional mixer products that wouldn't be there otherwise.
It might result in better overall performance than switching the signal
path, but it's not a panacea.
Ron AC7AC
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