Ferrite cores

DrTeeth

Is it pointless or a good idea to use ferrite cores on the earthing wires in the shack?

Thanks in advance.

Mike va3mw

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/CommonModeChokesW1HIS2006Apr06.pdf that made me a believer in RF Choking. The quieter you are, the more you can hear. 73, Mike va3mw

KY6LA_Howard

It's actually counterproductive to put ferrites on the earthing wires as you want the RFto go to ground.

DrTeeth

Thanks Mike. I have a bulk order  of 31s just waiting to be fitted. There is a nice photo on Al's (NN4ZZ) site (**** 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.

DrTeeth

Hi Howard,

Thanks for confirming that. Take care.

Walt - KZ1F

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

Al_NN4ZZ

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

Joe WD5Y

I use these and they work very well! http://www.kf7p.com/KF7P/Ferrite_chokes.html 73's Joe WD5Y

Tim VE6SH

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

73

Tim VE6SH

George KF2T

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..

Charles - K5UA

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.

DH2ID

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!

Walt - KZ1F

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.

WA2SQQ

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.

DrTeeth

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.

DrTeeth

Thanks for the link Joe. Lots of useful information too so saved as a PDF.

DrTeeth

@ 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.

Charles - K5UA

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.

Joe WD5Y

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

W7NGA

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 **** 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.

Larry _ NY8T

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.

Bill W2PKY

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?

G8ZPX

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

Drax

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.

Charles - K5UA

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.

Joe WD5Y

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

DrTeeth

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?

DrTeeth

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?

DrTeeth

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.

DrTeeth

As long as it is trad Jazz ;-).

Joe WD5Y

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