Hi Ted,
RF is weird at times and can be pretty frustrating. It seemingly defies
logic. I'm not sure if you are having the problem or your buddy but anyway,
you left out a few things: Are you running a low-pass filter in your
feedline to your antenna? If not, I'd get one and give it a try. There was
a LP filter survey article in QST a few months ago (it might have been last
year) in which a bunch of filters were reviewed. It is probably on-line
from the ARRL web site. You could look at it and select a filter.
You mention something about RF in the shack. Do you mean, RF in your tx
audio? That's a separate problem from the TVI in some ways, (but some
things you do about the TVI may help with the audio RF if you have any).
Besides the LP filter, I'd try a few other things. I hate to say it but you
may have more work to do. In my experience, a 1 kw amp needs a pretty good
ground. Depending on where you are, one rod may not be enough. I'd put in
at least two more, each at least 4 or 5 feet away from the one you already
have in. The one in now should be the center rod with the others coming off
it, each with its own strap from the center, i.e. don't daisy chain them.
It's better to have all this below grade also.
You don't say what band you are operating on when you cause interference.
If it's 10 meters your 10' ground run is just about a 1/4 wave antenna. If
possible, try to make it shorter, as in about 5 or 6 feet (hard to do I
know) so your gear sees a lower reactance on that band. I would also
recommend using either a heavier gauge cable such as 2/0 gauge from Home
Depot, or better yet, some 3" wide copper strap which is available in rolls
from AES and perhaps other vendors. Try to avoid sharp bends in your run
to the rods. Use the ferrite beads on your audio cables into your rig (mic
cord for example) if you have RF getting into your tx audio.
As always, do the easy stuff first such as trying the LP filter. That may
make a big difference. You don't mention if the tv is connected to an
antenna or cable service. It's real hard if not impossible to keep 1kw of
rf out of a consumer electronic product connected to an antenna that's near
the tx antenna. You have done a lot already--I'd try protecting the tv next
by putting a high pass filter in the line and looping the tv feed thru some
ferrite beads and putting the tv power cord on a line filter--it could be
looped through ferrite beads also. After all this, the tv front end may
simply not be cabable of rejecting a real strong out of band signal. Please
report back to the list on the outcome.
73,
Rob Atkinson
K5UJ
k5uj@hotmail.com
From: Ted Bohrer <N7QY@arrl.net>
To: rfi@contesting.com
Subject: [RFI] stealth RFI
To: <rfi@contesting.com>
Date: Sun, 15 Jun 2003 14:13:50 -0700
Well, All
My buddy has a RFI problem in the TV and home stereo. Here's the challenge.
(He has the Icom 756 Pro II, Icom linear and tuner, GAP Challenger)
------------------------------
THE SETUP TO DETERMINE EXTENT OF RFI PROBLEM-
"I turned on TV, sat the wife down, asked what channel was the worst, and
did a baseline test with Icom linear on (500w), voice and CW. The TV screen
does a little herringbone on key down full 500w and the speakers mumble on
SSB, worse with processor on."
INTENTED SOLUTION-
"So I tear out my grounding harness made of 1.5 inch braid bus bar and 0.5
inch braid straps going to each piece of equipment and replace it with
individual braid lines all going to the back of the Icom tuner, and the
tuner uses #8 ground wire on a 10' run to a 8' ground rod just outside the
shack. Then I installed a Radio Works T-4G grounded Line Isolator at the
Gap Challenger antenna hooking the isolator ground strap to the 10' ground
rod at the foot of the Gap.Then back in the shack I put T-4 Isolators (The
Radio Works: http://www.radioworks.com/clitop.html) between the Icom 756 Pro
II and the Icom linear and another T-4 Isolator between the linear and the
tuner. So after much cussing, cutting of finger on who knows what, writhing
in dust behind the rigs and multiple contortions working on the back of
equipment from the front, I declare the project done and RFI hereby gone."
THE TEST-
"So I sit the wife down in front of the TV again and fire off the rig to
show her how OUR $100.00+ worth of Isolators and ground rods had banished
the RFI. So I lay on the key while we are both watching the screen . . . .
. and.....
BIG blankety blank 4 INCH WIDE DIAGONAL BARS GO MARCHING ACROSS THE SCREEN .
. . 5 X 9 !!!
much more blankety blank, blankety blank. . . It is easy 3 times worse than
before I installed the line isolators!!!
So do I still have RF in the shack? Darned if I know, how am I going to
tell? Do I still have RFI on the TV? Oh yeah, big time.
Maybe, just maybe the RF on the coax is now gone, and there is less RF in
shack, but the result was more power to the antenna or a different pattern
which is pumping more RF into the house wiring which is really the way the
RF was getting into the system in the first place, thus more RFI at the TV.
I still have 4 split ferrite squares that I was going to put on the 110v
power cords of the TV and the Tuner box. I almost hate to do it cause I
have this sinking feeling it will make it even worse."
SO THERE WE HAVE THE CHALLENGE-
Can anyone make any suggestions for us?
Thanks and 73,
Ted N7QY
--
"What could possibly go wrong?" Laurel and Hardy
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
_________________________________________________________________
Protect your PC - get McAfee.com VirusScan Online
http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963
|