[ARC5] HF Converter - feeding mixer with a square wave?

[hwhall at compuserve.com]

IIRC, mixers DO have to operate in a nonlinear mode for much of anything to happen. I'm not sure that means that a square wave is a good thing to send into a mixer.

WayneWB4OGM

-----Original Message-----
From: Leslie Smith <lnsmith99 at gmail.com>
To: ARC5 at mailman.qth.net
Sent: Wed, Mar 16, 2022 9:35 pm
Subject: [ARC5] HF Converter - feeding mixer with a square wave?


ARC5 at mailman.qth.net
HF Converter - feeding mixer with a square wave?

Hi Wayne:  You might think (and correctly) that my question suggests I don't know much on this topic.  On another web-page David Newkirk published a circuit showing a 2N7000 FET in the cathode circuit of a 6SH7 mixer.  (I hope the attached circuit comes thru and is visible.)  

According to the datasheet for the 2N7000, it will turn on at about 2.5V (source to gate voltage) and by 3V be capable of passing 50mA.  That suggests (in my thinking) that the FET will quickly be saturated, so that a small LO signal switches the FET (rather than modulates it).  So - is not the LO oscillator a switching signal in Mr. Newkirk's circuit?  

Again, my understanding about correct operation of a mixing device was that it should operate (in approximately) class "C" - and so be conduction for approx 30 to 40% of the LO wave-form.  

Again, I emphasize that this is merely my interpretation of the situation; I welcome any correction to my understanding.  I know that most readers here know a good deal more about RF mixers (etc) than I do.  I hope to improve my understanding of this topic by reading answers on the ARC-5 reading list.

In the end I may take an experimental approach and try both a square wave and sine wave into the mixer circuit.  The main problem in doing this:  I don't have test equipment to measure any difference between the two circuits.

Thanks for your reply!

Leslie


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