Thought I'd fill you all in on the final chapter of my
little drama, in which N1EU triumphs after being
plagued unceasingly by horrible nasty RF-induced ssb
distortion from his Omni 6+/Centurion combo on 10, 12
and 17m.
I've had so many really helpful suggestions from many
of the TT reflector gang all along the way - many,
many thanks. And if I needed him to, Paul at Ten-Tec
offered to go above & beyond what I believe any other
manufacturer would have offered in helping to solve
the problem. And now, the story . . .
I was getting to the end of the rope. I had installed
bypass caps in the 961 & Omni where they seemed to be
lacking. I added gobs of ferrite everywhere I could
think of (almost . .) I was ready to replace the
internal audio wiring of my Omni when someone
"knowingly" told me it was unshielded (upon
inspection, found that it was not only shielded but
ferrite beads are on the lines as well). I stripped
the station set up down to the barebones -
disconnecting everything but the Omni, Centurion, 961,
dummy load and a mike - no improvement. I tried
different mikes. Reworked the station ground. Etc,
etc ad infinitum
The first glimmering came when I lengthened the
rig/amp coax interconnect from 3 feet to 6 feet and
found an improvement. (Hmmm . .) On a whim I stuck
my 238 tuner between the Omni & Centurion, nulled
reflected power and completely eliminated the problem.
(Double Hmmm . .) So I thought there might be a rig
problem, but first I wanted to try a really good choke
between the rig and amp. At the same time I got an
idea on how I could drive an 8 ft ground rod into the
subfloor almost right beneath the rig. I installed
the new ground system with a total run of 5ft of 1
inch braid between rig and rod (a shortening of 7 ft
from the old connection to the house entry ground rod)
- and used strict single point grounding for the
station. The new ground eliminated 90% of the
RF/distortion and the choke (currently a RadioWorks T4
Line Isolator, soon to be a homebrew job) eliminated
the remaining 10%.
Whew, what a relief! I learned at least two things
through all this - there's a lot of guys on the
reflector who really want to help, and RF ground
connections like to be S-H-O-R-T.
Thanks & 73 to all,
Barry N1EU
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