[R-390] Fan Power Supply Voltage and RTTY Question

[Scott, Barry (Clyde B)]

List,

Power Supply question:
I built a simple power supply to drive a cooling fan for my R390A.  I used an 18VCT in a "double half wave" rectifier configuration (the same way the R390A HV power supply is done).  I slapped a cap across the output (20mfd as I recall) and it was delivering a clean 14VDC no-load voltage on the scope.  Fine, I thought.  Good enough to drive some small fans.

Well, when I connect the fan, the voltage drops to about 9 volts (according to the DVM).  The fan is drawing about 120ma.  What causes the sudden voltage drop?  I need to look at the voltage on the scope, but I suspect the cap is discharged through the load between half cycles and the DVM "sees" 9VDC when, in fact, it is a rippled DC signal.  Does this sound plausible?

RTTY question:

When tuning for RTTY, I know tha most all of them are LSB and tuning to the wrong side of the signal will invert the mark and space signals.  When you tune through a RTTY signal -- say from a lower frequency, through zero, to a higher frequency, which "side" of the signal is the right "side": the one "below" the zero beat or the one "above" it?  I think this may part of my inability to copy RTTY correctly.  Last night I finally was able to get the "five number" coded patterns I've heard others talk about.  Sadly, I don't remember which "side" of the signal I was on...

Thanks,

Barry(III) - N4BUQ