[TenTec] some Confusion--Argosy Alignment

[Ken Brown]

>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