[RTTY] Rigblaster Pro Hum

[Charles Morrison]

I emailed West Mountain Radio about this and haven't heard back from them,
so I'm going to pose this question to the RTTY group.  

I've got a Rigblaster Pro, and have been using it for some time.  During the
SS SSB contest, a W6 told me that I had a hum on my signal.  So I began
investigating what the cause was.   I confirmed the hum with the monitor on
and the power on the radio turned all the way down.  I began removing cables
one at a time, until I got down to only the MIC input into the radio (even
pulled the power cable).  Pulled the mic input, and no hum, plug it back in
and a hum, definitely coming from the Rigblaster.  This was evident in SSB
and AFSK modes.

I picked it up from its position on top of the radio and moved it around.
Definitely affected the amount of the hum, but never quite got rid of if
regardless of position.  

I reached over and turned off the amplifier.  Bingo.  Transformer in the
Alpha.  So I turned it back on, placed it right on top of the alpha, biggest
hum in the world.  So I began attempting to find a location where I could
get the Rigblaster away from the alpha, but it turns out that the Rotator
Control box did it too, as well as the scanner.  At the maximum length of
the mic cable, I couldn't locate a quiet location.

I did a search, N6IT Garry had the same problem back a few years and posted
this question to the Writelog list.  I emailed Garry and he said he moved
his, but since I've moved it all around the desk, there's no where else to
go. Up, down, side to side, just slight differences, but no relief from the
hum.

Did some final experimentations and found the cause.  In the Rigblaster Pro,
there's the audio routing jumper block that allows you to "process" your
audio through the computer.  Set the jumper, flip the switch and load the
software and you can have "big audio" like the rest of the Double
Widebanders.    I enabled this to give me the ability to record SSB messages
in Writelog through the station mic instead of a computer mic.  Turns out,
if this jumper header is enabled, regardless of the position of the Process
switch, the Rigblaster picks up the hum of just about any nearby
transformer.  The alpha only did it when it was on, the Radio Shack scanner
only did it when it was plugged in, and the Rotator only did it when it was
on. 

Has anyone successfully used a Rigblaster Pro with the audio processing
circuit enabled in a shack with an amplifier transformer within the 2 and a
half foot reach of the Mic cable?   Currently I've cured it by changing the
header to disable and doing without the recording on the fly in Writelog.  I
use FSK for rtty, but was told that there were sidebands on my PSK signals
if the Alpha was turned on.  This has now cleared up since I changed the
jumper block back to disable.

Charlie
KI5XP