I am not entirely sure what it is I am trying to achieve with the scope and not
sure what they mean by triming r1 for mixer balance at 21.320.
I cannot say anything specifically about the Argosy.
Generally speaking in a "Balanced Mixer" the input signals feeding
through to the mixer output are minimized when the mixer is adjusted for
best balance. So for instance if the inputs were a 9 MHz IF and a 16 MHz
LO, and the desired output is 7 MHz, mixer balance adjustments will
minimize the amount of 16 MHz and 9 MHz signal on the output of the
mixer. There is another mixing product in the scenario, 25 MHz, that has
to be removed by bandpass filters or a trap. The 9 MHz IF, being fairly
close to the desired 7 MHz output, could still have significant power
even after bandpass filtering, if it were not "balanced out" by the
balance adjustments on the mixer.
A similar situation exists with "Balanced Modulators" in which the
"Carrier" is minimized by the mixer balance adjustment, leaving only the
two sidebands, one of which is passed through a bandpass filter and the
other drastically reduced by that filter. The carrier is on the filter
skirt where it would not be sufficiently attenuated by virtue of the
filter by itself. By balancing the mixer the carrier feed through can be
greatly attenuated.
DE N6KB
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