[R-390] IF Transformer, alignment and performance

[Tisha Hayes]

I have been lurking for quite a while, I continue to travel extensively and
rarely get to fire up my radios;

But on to sensitivity;

We know what S/N (signal to noise ratio) and receiver selectivity has
probably even more to do with receiver performance than just sensitivity,
expressed as either RSL in dBm, uV or S-units.
Once you get to the point where you are between 3 and 0.5 uV sensitivity
and you are still wanting more you find yourself chasing after ways to
improve selectivity.
I did a few things to improve selectivity; since I was not worried about
ESSB or wideband audio quality for BCB or SWL listening (I primarily listen
to SSB or CW) I went after the stagger-tuning on the IF
Going with a conventional alignment of the stages instead of an offset made
the radio more selective. Building a 12 KHz wide roofing filter between the
RF and IF decks helped as well.
Fortunately I live in a radio-quiet area where across most bands the
background noise levels are -110 to -115 dBm (S2-S3) when there aren't
thunderstorm crashes I can dig out some good ones off of the tail end of a
1600' beverage.

Trying to do better than -110 to -112 dBm RSSI required the use of a
Faraday cage and constantly swapping good tubes for good tubes to find the
quietest one. It reverted to black-magic and I wanted to do blood
sacrifices and scatter chicken bones for better results. That is when I put
a stop to that fools-pursuit.

*Ms. Tisha Hayes, AA4HA*

*Senior Engineer, 4RF*