Thanks Jim..
I'll read through where you suggested I read and see where I can improve my
system.
One thing you said, that I haven't done, and will, is to have a common ground
for the home theater systems. Gonna be tough for the home theater room, it is
upstairs and 150 feet away from the grounding pedestal. One saving grace: I
have no RF activity into the subs with the L7, only the Henry.
One thing I *did* do on both theater systems, was to use Cat 6 for the speaker
wiring. I forget where I heard to do that, I think it was on one of my home
theater groups.
As for your '2 line' mode being bad, I assume [ J ] you are speaking of twin
lead fed OCFD's. No issues there, I use coax as a feed, not twin lead. Twin
lead will not survive 100 mph winds, which are common at my location.
OK, off to do some reading!
Many thanks Jim. I will keep you posted on anything I read, that makes sense
as it pertains to my system(s), that I will have implemented.
Joe – W7RKN
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Jim Brown
Subject: Re: [RFI] RFI In My Shack
On 12/2/2017 9:25 AM, Joe wrote:
> A little different question. Perhaps some suggestions here:
>
> I have a new amplifier in the shack, a Drake L7, that is being used in
> place of a European version of the Henry 2K D Classic.
The description of your system sounds like a recipe for RFI. I've done three
tutorials on the topic. They are at k9yc.com. The most theoretical on is
k9yc.com/RFI-Ham.pdf BTW -- I tore up a lovely 18-in JBL sub-woofer about 15
ft from a dipole. It was in shreds before I realized it.
Several highlights.
AC line filters are a complete waste of money. They only work on differential
mode RFI (even though they say they do common mode) and nearly all RFI induced
on wiring is common mode. SO -- Ferrite common mode chokes are the solution
that works.
Poorly balanced antennas are a MAJOR cause of RF in the shack and the house.
Almost any antenna fed with 2-wire line will put common mode current on it, and
off-center fed antennas are the worst. The solution is a serious common mode
choke at the feedpoint, BUT off-center fed antennas put HUGE common mode on the
line, so any decent choke will FRY.
Any antenna that WORKS will put RF current on any conductors near it. We may
call them speaker cables or audio cables, but Mother Nature calls them
ANTENNAS. Nearly all equipment is built with a design defect called "The Pin
One Problem," which causes any current flowing on cable shields to get into the
equipment. If it's AF (power line fundamental and
harmonics) we hear it as hum and buzz; if it's RF, it gets detected and
amplified.
The solution is pretty simple -- start with proper bonding of all equipment in
the shack and any home entertainment setup. Add to that multi-turn ferrite
chokes on all wiring coming into those systems, and if you still have problems,
chokes on interconnecting wiring. Study this set of slides for a talk I've done
for several ham clubs and at Pacificon and the Visalia DX convention. It has
been a large part of the basis for N0AX's new ARRL book on the topic.
<http://k9yc.com/GroundingAndAudio.pdf> http://k9yc.com/GroundingAndAudio.pdf
Another mechanism couples RF from speaker cables to power amps. All audio
amplifiers have feedback around every gain stage to reduce distortion and
noise. The feedback network around the output stage of an audio power amp
couples any RF on the speaker cable back to the input, where it is rectified
and amplified. Two solutions for this. First, replace all zip cord used as
speaker cable, glorified or plain, with twisted pair. Twisted pair has been
used for more than a century to resist crosstalk, and is about 30 dB better
than zip cord in rejecting differential mode pickup. Second, if you still have
a problem, put serious ferrite chokes on the speaker cable.
As to why you have problems with one amp and not the other, I'd suspect issues
with bonding, or some combination of monkeys and typewriters writing
Shakespeare.
73, Jim K9YC
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