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Consider two things, ground loops and capacitor
bypassing where possible.
The ground loop can be a total killer at AF and a serious problem
at HF. Try to find ways to deal with it. It's often not at all
Capacitive bypassing is a good thing, too, when you can do it.
Attenuation comes from either or both increasing the impedance of
the path into a device and decreasing the input impedance. If your
input impedance is 1k it is going to take a few pounds of suitable
ferrite to attenuate signals. If your input impedance is 50 ohms
and the impedance of your chokes is 10k your attenuation goes from
about 20 dB to almost 50 dB. This input impedance would be your
common mode input impedance, of course. So it is likely to be
quite low at least for the shield side. Ferrite can help guarantee
that noise on the shield has less chance to leak inside. (All
cables leak RF. All you can do is negotiate with it over how much
Something to think about it the fact that if you have one ferrite
over a cable and add a second beside it, all you do is double the
impedance (6dB). If you can find a way to let cable between the
chokes have a low impedance path away from your receivers (and
lips on microphones) then you can go from doubling the impedance
to having cascaded low pass filters with a 20 dB filter plus a
second 20 dB filter giving you 40 dB rather than only 26 dB.
Design your solution rather than throw ferrite at it at random. A
really good resource to visit is Jim Brown's website
. He spent his
working life fighting emi and hum in a theater inside a building
in Chicago that housed several very high power radio and TV
stations - and making it work. He knows what he talks about.
On 20211119 07:43:20, Tom Crosbie G6PZZ
the true friend of the Radio Ham”
but it has to be the right type of ferrite to be effective.
Putting your own ferrites on your cables means you have a
much better solution for solving EMI/RFI problems.
shack is groaning under the weight of ferrite in place, much
of it doing nothing because it is cheap Chinese ferrite
bought because it fitted the cable more than anything else.
have a big EMI/RFI problem which is slowly diminishing as I
replace both cables and ferrites to make better common mode
chokes and filters. Using a trusted brand is a good start
but does anyone know the type of ferrite fitted to the Tripp
Lite leads that started off this discussion? I’m just
Good call there OB. Ferite the true
friend of the Radio Ham. 73 de John - G0WXU.
On Thu, 18 Nov 2021 at 15:13, jdow <jdow@...>
cables do this, too. I am not sure about HDMI. There are
a lot of HDMI cables with glowing advertising and claims
that aren't really up to snuff. Linus Tech Tips has the
testing on youtube. I am guessing much the same goes for
USB3 cables and Ethernet cables and....
On 20211118 06:53:29, Kriss Kliegle
It’s not just USB cables that have
poor RFI shielding. I was just at another Ham’s QTH
installing an over the air TV antenna for when the
power/cable goes out. When ever he turned on his
IC7610 with the external video monitor, he would loose
TV reception. TV antenna was in attic and rig in
basement, separated by +35’. On a hunch, I
disconnected the DVI Cable from the IC7610 (that
contains toroids on both ends) and TV reception
returned. I placed a few random, unknown value
clamp-on ferrites that he had in a drawer and all was
The hunch was from prior experience with a DVI
cable in my main operation position, the computer
monitor wipes out certain 440 band channels on my
Those with DVI cables in operation and use 70cm and
above may want to experiment with ferrites.
YMMV (Your Milage May Vary)
73 Kriss KA1GJU/AM