>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 19 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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