[Drake] R4C Filter loss/mode independent of bandwidth selection

[Garey Barrell]

The later R-4C's use a "T-7C" transformer that is tapped to 
provide a better match to the narrower filters.  At least 
that is the explanation I heard or read somewhere!.   My 
21000 schematic has the T7C, but the 18726 schematic does 
not.  All of my R-4C's are above 21000, and the two I just 
tried both show less than 1/2 S-Unit drop from 2400 to 1500 
or 500 Hz, and a little over one S-unit to 250 Hz.

There are a couple of changes that can be made to improve 
the situation in the older receivers.  One is to replace the 
white "microphone" cable from T9 to the switch and from the 
switch to T6 with RG-174 or similar small coax.  Another is 
to replace C49 (390 pF) with a 430 pF.  Obviously IF 
alignment is critical on the 250 and 500 Hz.

73, Garey - K4OAH
Atlanta

Ka9p@aol.com wrote:

> Thanks Harvey.  Unfortunately it's an early one.  I did carefully go thru a 
> tweak things this AM and found about a 3 dB improvement (thanks).  It's still a 
> bit of a dog, but you've inspired me to look and see if there is some other 
> way to optimize the match a bit just in case.  73, Scott
> 
>