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

[Bob Groh]

Wayne, actually a square wave is a darn good LO - at least for balanced
diode mixers. Basically the mixer is adding as a switch and the LO is the
doing the switching. Considerable amount of technical analysis on this
'back in the day' - was the hot setup for high performance receivers in the
1960s and 1970s.

Bob Groh, WA2CKY

On Wed, Mar 16, 2022 at 10:47 PM <hwhall at compuserve.com> wrote:

> 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.
>
> Wayne
> WB4OGM
>
> -----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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