The dreaded "simple RF overload" is rare. Most RFI problems are caused
by RF in the shack, which gets into power lines, etc. When you DO have
the former problem, it's treated by installing ferrites on the
"antennas" of the devices interfered with, e.g. power, speaker, or phone
lines. ONCE I had to cover a CO detector with aluminum foil, but most of
the time the problem was solved by ferrites on the external leads.
I am running 1.2 kW with a dipole about 8m above the roof of my apartment.
73,
Victor, 4X6GP
Rehovot, Israel
formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
On 27/11/2022 4:00, Al Lorona wrote:
Here's a statement: "RF in the shack" does not equal "simple RF overload". Let
me define my terms.
"RF in the shack", which many people have experienced when using "unbalanced"
antennas like verticals, off-center fed wires, and others, is caused by radiation from the outside
shield of the coax, or by unequal currents on either side of a balanced transmission line. As you
know, this causes everything from interfering with household devices to RF burns. Many folks have
cured this kind of problem with various ferrite chokes and grounding.
But there's another kind of interference: that caused by "simple RF overload",
which occurs when your beautifully balanced antenna, with lots of ferrite all over the
place, judicious routing of the feedline, and good grounding, is radiating so well that
the RF field around the antenna-- and thus, inside your home-- is very high.
Paradoxically, this is what you want to happen; your highly efficient antenna system is
turning your RF power into a nice, strong radiated field.
So it's important to understand the difference between these two mechanisms.
Maybe a story will help you further understand the distinction I'm making. I
attended a high school not far from 50 kW radio station KRLA. KRLA used to get
into everything. It was so loud on a crystal radio that you could hear it
easily with the earphones laying on the benchtop. If you left an oscilloscope
probe disconnected the scope would show an enormous 10V peak-to-peak signal on
the screen.
Was KRLA guilty of RF on its feedline, putting "RF in the shack" into our electronics
lab? Would ferrites and additional grounding at KRLA's antenna have improved anything? No, because
it was a case of "simple RF overload"... caused by a very strong, very close transmitter.
KRLA was doing exactly what it should have done: put a bodaciously loud signal everywhere. We just
happened to be 'in the way' of that signal.
This is what can happen when you have a perfectly good and RFI-proofed antenna
system. The radiated signal is simply too strong for various electronics in
your house to handle. And, as you can imagine, running the legal limit makes
the problem worse. This is what I was trying to communicate in a previous post.
I had essentially asked, "Given that your properly functioning antenna is putting a
bodaciously loud signal everywhere, why are some devices immune to the signal, and yet
others fall apart? Why does one ham's garage door opener go crazy when he transmits, but
another ham's is unaffected?" That's what I was wondering.
A number of respondents to my other post told me that yes, in fact, there are
devices that act naughtily when they operate high power, but at least as many
said that they've *never* had any such problems. Isn't that interesting? Is it
just luck? I've purchased faulty devices while they lucked in and purchased all
good ones? The engineer in me hates this arbitrarity and drives me to
understand why.
What are the unaffected hams doing differently than the rest of us, if anything, to
prevent not "RF in the shack", but the dreaded Simple RF Overload?
To keep the reflector quiet, maybe you can email me privately and I can post a
summary of comments later on. Or not, if you're sick of the topic.
Thanks!
Al W6LX
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