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

[hwhall at compuserve.com]

Will a square wave produce a "family" of intermodulation signals that I find undesirable?
Very likely. Why not put a filter on the divider output, though? It's a fixed frequency so I should think you could make a very good filter & have a good sinewave to send the mixer.

WayneWB4OGM

-----Original Message-----
From: Leslie Smith <lnsmith99 at gmail.com>
To: arc5 at mailman.qth.net
Sent: Wed, Mar 16, 2022 7:23 pm
Subject: [ARC5] HF Converter - feeding mixer with a square wave?


        HF converter - 80M to BC-453 tunable IF.
        
I wish to build a simple solid state converter to bring the lower part of 80m down to suit a BC-453 working as a tuneable IF.   The LO frequency would therefore be 3200kHz.  Crystals are readily available for 6400kHz.  Consequently I am considering dividing the crystal frequency by 2 using a JK (or similar) digital divider.   This raises a question.  Normally a mixer is driven with (something approximating) a sine-wave - a signal with no harmonics.  A digital divider provides a square wave, with many odd harmonics in the signal.  The amplitudes  of the harmonic fall progressively, so that the third has an amplitude of one third the fundamental.  The fifth fifth - one fifth and so on.  You can check this easily using MS excel spreadsheet.  (or just trust Mr. Fourier).

Question:  How will the presence of these harmonics affect the operation of the mixer.  Will a square wave produce a "family" of intermodulation signals that I find undesirable?  Am I chasing the wrong birdie up a tree?

Leslie

PS - 3200kHz crystals are available, but not so easily got as crystals for 6400kHz, so the idea of using a sine-wave isn't out of the question.  


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