[ARC5] Update on first IF mod

[J Mcvey]

I played a little more with the R-27 selectivity mod yesterday.
To compensate for the looser coupling loss from increasing the distance between the coils, I jumpered R-9 (1st IF cathode resistor) with an 820 ohm resistor.
The radio seems to have the same sensitivity as a before now.

Ironically , when I compared the two IFs ( one modified, one not) on the spectrum analyzer, they didn't look all that different. However, I think that may have had more to do with the low levels I was using to drive the cans and impedance matching which probably affected the overall Q in both tests.

In practice, there is a noticeable improvement in selectivity which is , of coarse, most noticeable in the CW area. 


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