The impedance increases with the square of the turns. 2 turns = 4 times
the impedance. It would take 4 chokes in series to equal one choke with
2 turns. A "turn" is one pass through the middle. More turns is better
until we get to very large chokes where the inter-coil capacitance
lowers the impedance.
Buck, K4IA
DXCC Honor Roll
8BDXCC
Author EasyWayHamBooks.com
On 12/20/2021 9:49 PM, David Herring wrote:
Pete,
Yes. You either have to have lots of them, or you need to get bigger ones and
run multiple turns through them. Also get the right “mix” for the frequency
range in question. Type 31 is pretty good for HF.
Not an expert, but studiedhttp://k9yc.com/RFI-Ham.pdf
<http://k9yc.com/RFI-Ham.pdf>,http://k9yc.com/RXChokesTransformers.pdf
<http://k9yc.com/RXChokesTransformers.pdf>,http://k9yc.com/GroundingAndAudio.pdf
<http://k9yc.com/GroundingAndAudio.pdf> and others athttp://k9yc.com/publish.htm
<http://k9yc.com/publish.htm>. There is a wealth of information there, available for free.
73,
Dave - N5DCH
On Dec 20, 2021, at 7:21 PM, Pete Smith N4ZR<[email protected]> wrote:
Others can speak more authoritatively about this, but I thought those clamp-on
cores, where they go right on the existing run of coax, offered too little
inductance to be of much use below VHF. Experts?
73, Pete N4ZR
Check out the new Reverse Beacon Network
web server at <http://beta.reversebeacon.net <http://beta.reversebeacon.net/>>.
For spots, please use your favorite
"retail" DX cluster.
On 12/20/2021 8:02 PM, Bob McGraw wrote:
For those using the clamp-on ferrite devices, when installing them, be sure
part A closes completely and solidly contacts part B. Otherwise, there is no
flux path and the device is ineffective. If it is closed and loose on the
cable, then that's good. If it is closed or difficult to close, it isn't
large enough for the cable and will likely not be effective. Any gap between
the halves renders it worthless for the application.
73
Bob, K4TAX
On 12/20/2021 6:18 PM,[email protected] wrote:
Message: 11
Date: Mon, 20 Dec 2021 08:34:24 -0800
From: Dave<[email protected]>
To:[email protected]
Subject: Re: [Elecraft] RFI
Message-ID:<[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
Hi,
Purchase some FT240-31 ferrite cores,
(https://www.farnell.com/datasheets/1912768.pdf), and wind at least 5
turns of each cable going to, or from, the computer through the ferrite.
I have several of these, and they stopped ALL of my RFI issues with my
computer, and with a weather station I have as well.
Shop around looking for the best price, some folks are asking 10 bucks
for one of these, others are asking 5 bucks... I use Newark, and
Digikey as my goto places.
Also look to K9YC's site, for more information on how to make the chokes...
http://k9yc.com/2018Cookbook.pdf
73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources
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