Ferrite cores

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  • Question
  • Updated 3 years ago
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Is it pointless or a good idea to use ferrite cores on the earthing wires in the shack?

Thanks in advance.
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DrTeeth

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Posted 3 years ago

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Mike va3mw

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Official Response
Ferrite cores should always be used, but not on the ground lines. You need them on feedlines both near the antenna and near the radio. Power lines, both AC and DC.

I have ordered them in bulk (Mix 31 and Mix 43). It was after reading http://www.yccc.org/Articles/W1HIS/Co...
that made me a believer in RF Choking.

The quieter you are, the more you can hear.

73, Mike va3mw
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DrTeeth

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Thanks Mike. I have a bulk order  of 31s just waiting to be fitted. There is a nice photo on Al's (NN4ZZ) site (damned if I can find it now) showing the back if his kit with ferrites applied. I do have it on my computer, but do not have the right to post it.
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Walt - KZ1F

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I remember Al's picture Guy. I figured there had to have been a sale that day.
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Al / NN4ZZ

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Hi Guy,
Here is a link to my web page with the RF mitigation and ferrities.  Feel free to post the link or any of the pictures.   

http://www.nn4zz.com/FLEX6700.htm#RF_issues_and_solutions

Same with the link for the fiber setup which is also an RF mitigation solution.

http://www.nn4zz.com/FLEX6700.htm#Ethernet_Lightning_Protection

@Walt, yes I bought a box of them (hihi), figured it was well worth it for both fixing the lockups I was having as well as minimizing noise for DXing.


Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com
6700 - HW.................... V 1.6.21.77
SSDR / DAX / CAT...... V 1.6.21.159
Win10
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Tim VE6SH

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I followed Al's advice to the letter and it cured all my RFI issues!

73

Tim VE6SH
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DrTeeth

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@ Al - NN4ZZ

Thanks for the link and permission to post any photos here is they would be useful. I actually have the 6700 page saved locally as a PDF as it is VERY useful.
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KY6LA - Howard, Elmer

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Official Response
It's actually counterproductive to put ferrites on the earthing wires as you want the RFto go to ground.
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KY6LA - Howard, Elmer

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@Charles

Simple answer is that there is no simple answer
RF textbooks and engineering codes stress the need for single point RF grounds to provide a path that minimizes radiation ground loops. However the path length depends on frequency and length of the ground connections.

I suspect the results you got were likely because your grounds were too long so they were reactive to the flow of RF to ground.

Simple experiment. When your ground leads are too long, you can actually tune the ground lead to eliminate stray RF. MFJ makes a very effective ground tuner MFJ-459
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DrTeeth

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It does not look like the MFJ-459 is a current product. Do you have the 'official' name handy so I can do a search for an updated product?
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Walt - KZ1F

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Guy, I recall that it is called Artificial Ground.
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DrTeeth

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Hi Walt,

I found it. Looks like it is the MFJ-931 in their 2016 catalogue. Now just to find out if it is snake oil or "does what it says on the tin".
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KY6LA - Howard, Elmer

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Sorry I quote the wrong part #. I m in The South of France with too much good wine]

Yes it can solve a lot of issues. I used it to solve a lack of reasonable ground from the 19th floor of an apartment building. I have mentioned the MJF Srtificial Ground a few times on the\is Community and several people have reported success with it.
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Joe WD5Y

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I use these and they work very well!
http://www.kf7p.com/KF7P/Ferrite_chok...

73's
Joe
WD5Y
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DrTeeth

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Thanks for the link Joe. Lots of useful information too so saved as a PDF.
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George Molnar, KF2T, Elmer

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While we are at it, don't forget that the best possible quality feed lines should always be used. High percentage braid works wonders. Large surface area ground straps, too. Ferrites are great, but should usually be the cherry on top of good cable & wiring practices..
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Alex - DH2ID, Elmer

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I concur, George. MOF the US Army helped me out there with surplus milgrade cables, double copper shielded and teflon cored, when I was at Heidelberg and visiting ham friends at USAREUR.... some 35 years ago, and the cables are still like new!
(Edited)
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WA2SQQ

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First question, without any cores do you have an RF problem? If you don't, don't try to fix what's not broken. In general I find that my 6500 has absolutely no RF issues even while using my ACOM amp.

When I had my 5000, I had RF issues on certain bands despite using 1" copper braid. There was an article in the 5000's knowledge base that explained how a ground cable can still be resonant and thereby not effective. The solution was to use a length of heavy cable, like RG-11. At one end, tie the center and shield together. At the other end, connect the center to the shield using a .01  1KV cap. U this as your ground cable  connection. This arrangement provides both a DC and RF path to ground without any resonance. That cable by itself got rid of all RF on all bands.
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DrTeeth

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Hi,

The problem I do have is that the computer that I would prefer to use loses its wired Ethernet connection when transmitting on full power. Currently using a laptop which seems to work fine, though some of the bar meters fluctuate in SSDR on full power. It does not seem to affect the signal. I mainly operate JT65/9 at present and only use full power to get a difficult long-distanced one for the log.
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Larry - W8LLL

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Last year I was having rf related disconnects only while doing digital modes so I put some mix 31 chokes on my Ethernet cables and that solved the problem.

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Bill W2PKY

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Guy, I had a pig tail ehternet port that would fail when I transmitted. Tried another pig tail unit that worked just fine. Maybe try a different ethernet port?
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G8ZPX

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Guy,

If its only Ethernet that is the problem then why not put either a wifi card in the PC and get rid of the Ethernet, or use an ethernet-fibre adaptor to break the RF conductive path?   The slippery RFI sucker cannot get down fibre!

Or, get an ethernet cable about 3 metres longer than actually needed and then put 10 turns on a 31 mix ferite at each end.

If I buy any more ferite I will have to improve the foundations of the house!

73 de Steve G1XOW
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DrTeeth

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Wow Steve, that's sharp thinking mate - a Wi-Fi card. They are so dirt cheap it could be worth a punt. I'm off to check then out at the moment and see if there is any speed performance hits. Luckily, my router and run on 2.4GHz and 5 at the same time.

@ Bill W2PKY
Thanks Bill. I'll add it to the list of things to try.
(Edited)
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W7NGA

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As an old RF engineer, my mantra is that there are no rules. Just when you think you understand RF currents, their paths, their predilections ... your intuition will fail you. All you can do is play jazz and hopefully blow the notes that shift the mood in the desired direction. Many, many times, ferrites will exacerbate a situation because the root cause is not fully understood or assessed. I systematically work my way .. as if I were an errant electron looking to raise havoc. Often, rearranging and restacking radios will have greater influence that a dozen ferrites haphazardly placed.
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DrTeeth

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As long as it is trad Jazz ;-).
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Drax

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Most hams use too little ferrite (or just air coils of coax) to make effective common mode chokes especially on the lower bands and never get to hear the benefit.  

I use twelve 3-inch O.D. type 43 toroids in 2x6 binocular stacks on each end of my coax runs.  And 24 cores on each end of my 160 meter coax.   I also did my ethernet cables, rg6, USB cables, and wall wart cables with single cores.

You have to use a lot of cores because you can only fit 2 or 3 turns in a core and you want to get 1000 ohms or more inductance.

And you need to be using wide copper strap for the ground connection.  Not 20 feet long, but like 3 to 10 feet that fans out in a star configuration or bus bar.    I see guys using 14 gauge or  a crumple of old RG8X shield and that's worthless for an RF ground.  

And I ground the computer case which I made sure was all metal when I bought it.

Insane amount of ferrites, yes.  But I pick up Zero stray noise and I no longer interfere with the 24 MHz uplink stream on the cable modem when on 12m.

(Edited)
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DrTeeth

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Drax,

Thanks for the pictures. Why type 43 ferrite? I thought type 31 was the best to use at HF? What is the inner diameter of those 3 inch ferrites?
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Drax

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There's the datasheet for what I used.
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Drax

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And here is the explanation. http://www.yccc.org/Articles/W1HIS/Co...
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Tim - W4TME, Customer Experience Manager

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Please refer to this HD article on RF grounds, Grounding Systems in the Ham Shack - Paradigms, Facts and Fallacies

It will help for those wanting to know more on RF grounding.
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DrTeeth

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Put loads of ferrites (3 each end) on UTP Ethernet cable as well as earthed PC case, and still connection craps out. Getting USB wireless adaptor delivered tonight to see if Steve's idea works.
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Ian GM4KLN

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Excellent thread, thanks to all contributors!
I am optimising my 6300 based station which is 99.99%  for 50MHz (JT modes and CW): just seeking advice on whether the type 31 cores are still the optimum solution at 6m?
No specific issues - just trying to make the quietest possible environment for weak-signal work. 
tnx
73, Ian 
(Edited)
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Steven G1XOW

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Ian,

this is a very good starting point. "How to build a quiet station"

https://www.dropbox.com/s/kffp92esffo3zy5/How%20to%20Build%20a%20Quiet%20Station%20V2.pdf
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Ian GM4KLN

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thanks Steve, yes it is: I was just not sure if type 31 is the optimum for 6m, before I invest some £££ 
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DrTeeth

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Ian, I do not know the specs, but have a look at Type 43 ferrite materials.
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Varistor

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Mix 31 is specifically optimized for low frequencies, i.e. 10 MHz and below. Mix 43 is optimized for higher frequencies, but there likely is even better one for 6 m. Go to the Fair Rite site and look at their online catalog that shows the impedance of different mix types at various frequencies.

Note that I would recommend you stack different types to build yourself a choke that covers everything from 160 to 6 m.
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Ian GM4KLN

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Steve, Guy, Rudy: thanks comments and advice. 
glancing through, 43 seems the best compromise on 50MHz, as 61 is 200MHz+ range..but will research deeper to confirm. 
73, Ian