[Elecraft] RFIth

[David Herring]

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 studied http://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 at http://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 <pete.n4zr at gmail.com> 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, elecraft-request at mailman.qth.net wrote:
>>> Message: 11
>>> Date: Mon, 20 Dec 2021 08:34:24 -0800
>>> From: Dave<dave at nk7z.net>
>>> To:elecraft at mailman.qth.net
>>> Subject: Re: [Elecraft] RFI
>>> Message-ID:<8cdb19ae-b111-5a6c-3f2a-d29efdd25351 at nk7z.net>
>>> 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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