Ferrite cores

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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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DrTeeth

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Hi Howard,

Thanks for confirming that. Take care.
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Charles - K5UA

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Hi Howard,

This may seem counter-intuitive, but after years of fighting RFI issues I finally resolved them by removing the station ground.  All RFI issues just went away after that.  Since the station ground is an electrode in the earth and can not be considered a "safety" ground because it will not trip the AC line breaker (even if directly connected to an AC outlet), I had no reservations doing that from a safely point of view.

This RFI experience, which is not unique to my station, seems to contradict the RF grounding concept.  It brings up the basic question....does RF have an affinity for ground?  If RF has an affinity for ground, why doesn't a grounded, shunt-fed tower simply dissipate the RF directly to ground?

I have asked this question lots of times but have not had an answer that convinced me that RF has an affinity for ground.  Have there been any peer-reviewed publications that demonstrate RF on grounded equipment transmitting equipment will seek ground and be dissipated?

Thanks for any information you can provide on this.
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Walt - KZ1F

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Charles, I've wondered about that as well and assumed the answer was resistance of a parallel circuit. For RF you don't want a path long enough to act as an antenna and radiate the rf.
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Charles - K5UA

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Hi Walt,
That is partly why I asked the question.  If RF has a true affinity for ground, why would a ground wire radiate. And if it did, would not that induced radiation be very much less than the primary radiator (the antenna).  And if the antenna RF is not causing a problem at its magnitude, why would a ground wire, re-radiating induced RF at a much smaller magnitude than the antenna, cause a problem?

In scientific papers, all statements, however intuitive, must be referenced by peer-reviewed publications supporting the statement.  There can be no "everybody knows that" statements.  I'd like to know if there is any references in the IEEE literature that scientifically demonstrates that grounding a wire that is radiating induced RF will stop the radiation by dissipating the RF into the earth.
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Joe WD5Y

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Charles,
Just a question, do you still connect all of the equipment together with ground connection as common between each device? Or will the connection between each device possibly radiate? I fought rfi at one point and it was eliminated by common mode choke on coax, nothing I did with grounding helped at all, sure would be great to know a definitive answer.

73's
Joe
WD5Y
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Charles - K5UA

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Hi Joe,

I still have all my equipment on the desk bonded together at a common point to reduce the possibility of ground loops causing audio hum.  I use a lot of 2 inch diameter Mix 31 ferrite rings with 12 - 16 turns through the ring on audio and RF lines.  But I had all that before and was still getting RF into the audio when the rig and equipment was connected to a ground rod right under the floor of the mobile home.  As soon as I removed the ground, the RFI disappeared. I was astonished, even though I had hear other amateurs talk about this.  The ferrite cores make sense to me, but I just can't make sense of ground being an RF "sink".  Maybe there are scientific articles proving it, but I have not seen them yet. As I mentioned before, "everybody knows that" will not be a convincing answer for me.
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Joe WD5Y

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Thanks for the information. I plan on re-visiting my setup and will try what worked for you, as I mentioned before the common mode chokes helped a lot but I still feel there could be some improvement.

Thanks and 73's
Joe
WD5Y
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DrTeeth

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TBH, I think the solution to RF issues is more akin to witchcraft than pure science. Just think about it for a moment. We have a weird issue and after a process of deduction does not have a definite cause so it gets labelled as an 'RF' issue of one type or another. Then we have a slew of 'solutions' which work for on ham and nobody else. Then there are many other solutions until something works. Because of the nature of the beast, we do not know if it is one thing we have done or some combination which just comes together in one shack.

No where is my black cat and jar of lizard giblets?
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Joe WD5Y

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Ha Ha, good one and I totally agree. On a serious note I have wondered if there is a rf sniffer device available to help search for the rfi origin? I believe mfj used to make something along these lines, not sure? This might not be a solution but if available could at least let you know of the offending source.

73's
Joe
WD5Y
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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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Varistor

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I am sorry if I have missed the answer to this question- what antennas do you use? RFI starts with the antenna, not with your rig, computers, etc. Using a wifi adapter doesn't make the RFI goes away, just hides it.

Can you please describe your antennas? How do you feed your antennas and how do you make sure the feed line does not become a radiator?
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Mike va3mw

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RFI is more than the antenna. It is all other antennas as in power leads, speaker leads, cat 5 cables and more. They can all receive band radiate RF.
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Varistor

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The guy stated that he has RFI problems when he transmits. All solutions so far have been focused on reducing the impact on affected equipment rather than dealing with the root cause.
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Steven G1XOW

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Guy, the number of turns is way more important than the number of cores! Aim for 8-10 turns each end. 
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WA2SQQ

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If the RF is causing problems to the PC, you need to determine how the RF is getting into the PC. With the PC operating, disconnect as many cables from the PC as possible. I’ve found that placing multiple cores is not as effective as winding as many turns as possible through the core. If 6 turns is possible, I wind 3 turns in one direction, and three in the reverse direction.

I suspect the keyboard and mouse as being the biggest possibility.

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KY6LA - Howard, Elmer

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Reactance varies with the square of the number of turns. So more turns the higher the reactants
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DrTeeth

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@ Steve G1XOW
The wireless idea did not work sadly.
I have only got clip-on ferrites, type 31. I bought loads of them. I do not have any other type. I have just put many more ferrites on without success. I would replace the motherboard and CPU if I knew it would work. All other PCs work okay, there are two others on the shack.

@ WA2SQQ
No joy. I suspected the USB cables and I removed them all.

The Ethernet cable has 5 clip-ons at each end. I am not even getting any improvement in that I can radiate more power before the cut-off.

I have some larger diameter ones that I should be able to get a couple of turns through, that did not work.

Any further ideas welcome. It would be nice to get it sorted before some major surgery on 29th ;-). I am happy to try some larger diameter ferrites for winding. I only have one reference to one but if anybody can supply others, I'll give ANYTHING a try.
(Edited)
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Varistor

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Try fixing the root cause. Fix your antennas.
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DrTeeth

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@ N2WQ
Got ferrites on the coax, at both ends. Only 1 out of three PCs in the shack has a problem, and only a specific one at that.
(Edited)
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Joe WD5Y

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Guy,
I know it's very frustrating fighting rfi, it's like looking for a ghost or moving target. All I can say is what worked for me as others here have posted. I did go the route of eliminating common mode interference on the antenna coax. I used two of the common mode chokes that I listed in my earlier post, these are made with the kit sold from K7FP with the rg142 coax and the dual cores. It does take some soldering to complete but did work as I had rfi issues even in my audio and PC. I also noticed improvement in receive quietness.

73's and don't give up,
Joe
WD5Y
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Varistor

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Guy, you never took the time to describe your antenna and how you feed it.

Start with the feed point, not the shack. If you don't have a proper balun/choke at the feed point you will continue seeing RFI.
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DrTeeth

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I have an end-fed with 9 clip-on ferrites at the feedpoint, which did not make any difference. Unfortunately, I have used some thick coax that is not too flexible. I think I will have to replace it with the more usual type if I am going to be able to coil it. There is a balun at the feed-point, but I have yet to connect any earth or counterpoise to it. Any work on the antenna will have to wait until my health improves; I will have a very long recovery.
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Drax

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That's too few ferrites to do anything on HF frequencies.  You would need like 100 of those kind.
(Edited)
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Varistor

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Guy,

I am sorry to hear about your health issues. This certainly makes your task much more challenging.

Your end-fed antenna is prone to RFI. You need a serious choke at the feed point and 9 beads are far from enough. My recommendation is to buy the proper balun from Balun Designs so you can feed and filter out the common mode at the same time. Unfortunately this will have to wait until your health improved.

Next, you may want to look at your rig and amplifier. Make sure you properly tune the amp as improper tuning does result in RFI. Finally, borrow a low pass filter and insert it between the rig and the amp; you want to make sure you don't send any harmonics up the feed line.
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WA2SQQ

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Guy - If you disconnect the network cable, all USB connections, speaker and AC power, do you still have the problem? If you do than it's probably safe to say that those connections are not how RF is getting in. With all due respect, those snap on chokes are only good for minor problems. Once you determine what cable it is, get a large core and figure out how many turns you can put through it. Place half as many in one direction, and the other half in the other direction. I destroyed my telephones on 160m. I used this method on the line to each phone and on the mail line as it enters the house. At full legal power, no more RF problems. My cores were about 6cm in diameter.

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DrTeeth

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@ WA2SQQ
"Guy - If you disconnect the network cable, all USB connections, speaker and AC power, do you still have the problem?" 

If I do that the computer will be off, hi hi. I disconnected everything except the power and the Ethernet cable and the problem still occurs. The only problem is that the network connection is lost when I transmit.

@N2WQ
It looks like I am going to have to rewire my antenna. I stupidly used quite a wide and inflexible type of coax. I will have to get 'normal' coax so I can get a serious choke at the feed point. Tuning is fine, down to 1:1 on every band except 12 and 6 meters.
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WA2SQQ

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So here is one possible solution.
Can you temporarily set up a wireless connection to your router? If that fixes the problem than you know, for certain, that it's coming in via the CAT5 cable. I added an Ethernet to fiber converter to my shack PC to guard against any lightning getting in via the copper cable. Such an adapter would surely kill any RF physically getting into the PC.
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DrTeeth

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I really think I am going to rewire my shack from scratch, putting into place all the useful things I have learnt here. Thank you to those who sent me emails rather than clagging up this forum. Let's hope my back recovers this time eh?
(Edited)
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George Molnar, KF2T, Elmer

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Good luck, Guy! Stay healthy.

Hey, while you're rebuilding, consider a conductive screen around the operating position. Provides a nice, low-Z sink and some shielding, to boot. I have a 3x10 ft screen behind my desk.

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DrTeeth

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@ George KF2T Thanks for your kind wishes and thenks for the idea.

@ Kevin K4VD That is something to bear in mind, thanks. Link bookmarked. I think I would like to try the rewire as there is much to do better.
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DrTeeth

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@ WA2SQQ
Sorry for my earlier misunderstanding. I borrowed a wireless adaptor and the network connection died even when the Ethernet cable was disconnected. I don't know if that gives anybody any clues as to what is going on.

Somebody sent me links to UK suppliers of the type of large ferrite rings and quality baluns that you state side chaps have sent. So good to go once recovered.
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KY6LA - Howard, Elmer

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@Guy

When you earthed the computer case, did you scrape the paint off all the screw connections in the case so that it was a complete Ferraday Shield? I found that even a Small amount of paint will stock conductivity and leave the case floating. Also put ferrites on the computer power leads and all the monitor leads.

One trick I use to find where the RFI ingress is to use a very large ferrite that I clamp on every lead. Once I discover the offending source, I use just enough smaller ferrites to fix the issue.

BTW. Fixing RFI seems to be a never ending issue as you only have to move a single lead somewhere and it magically reappears.
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DrTeeth

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Hi Howard,

I fixed the lead to bare/unpainted metal, but the side panels are painted. They slide into bare metal but I will have to check the panels themselves. Thanks for the heads-up.

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WA2SQQ

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Guy I think you are getting closer to finding a solution. Seeing that the wireless connection didn't solve the problem, we can probably conclude that your CAT5 INTERNET connection is not the main source of unwanted RF. When you loose the connection, I assume you also loose the connection to your FLEX? Try making a CAT5 choke for the Flex to PC interconnect cable. Take as many turns  as you can and pass them around and through a larger core. One other thing to consider - if you connect your devices through a hub or switch, try replacing it with another. It might be the active device that is inviting RF into your PC.
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DrTeeth

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@ WA2SQQ
Thanks for your optimism! It is well needed. I have bought some big enough toroids of type 31 material to make some nice chokes.
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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