Ah, OK, an AUDIO mixer is not at all the same thing as an RF mixer (which
I'm sure you know, Russell). An audio mixer is just a summing amplifier
(which I suggested this might be much earlier in this thread). An RF mixer
is essentially a multiplier, to achieve heterodyning. It may be implemented
as a true analog multiplier (log-sum-exponentiate circuit, or Gilbert cell
over a narrow range of amplitude, or a multiplying DAC) but more often is
implemented as simply a non-linear amplifier fed by both signals or even by
diode or transistor switching circuits which just turn one of the signals
into a square wave and switch the other signal on and off in time to the
square wave, yielding not only the desired product but also various
harmonic products, too, and not responding much to small changes in the
amplitude of the LO input.

Using dual-gate FETs allows the LO to shift the operating point of the two
FETs which changes the gain of  their response to the RF input, hence
multiplying action.


On Fri, Sep 30, 2016 at 2:04 AM, RussellMc <apptechnz@gmail.com> wrote:

> Here is a functionally identical ciruit using MPF102's EXCEPT they have n=
o
> emitter/source resistor.
>
>
> http://www.seekic.com/circuit_diagram/Audio_Circuit/Mixer/
> SIMPLE_UTILITY_MIXER.html
>
>        Circuit diagram only
> <http://www.seekic.com/uploadfile/ic-circuit/s2009795657611.gif>
>
> Here is a RF mixer  RF + LO to IF with commoned drains BUT they use dual
> gate FETs
>
>
> http://www.next.gr/uploads//112/Balanced-mixer-circuit-
> consisting-of-two-dual-gate-field-effect-transistor-formed.png
>
> _________________
>
> This not quite the same arrangement separates emitter but commons
> collectors - used as a colour channel separator in a mechanical TV system=
 -
> sounds like a black hole :-)
> Circuit http://www.hawestv.com/mtv_color/colorize_images/inv_mixer.gif
> >From here  <http://www.hawestv.com/mtv_color/mtv_colorize2.htm>
>
> _________
>
> Event Horizon - mechanical TV page - legion
>
>       http://www.hawestv.com/
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
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