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Ferrite cores

2

Answers

  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited March 2017
    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.
  • DraxDrax Member
    edited June 2016
    There's the datasheet for what I used.
  • DraxDrax Member
    edited June 2016
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited June 2016
    @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
  • DrTeethDrTeeth Member ✭✭
    edited August 2016
    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?
  • Walt - KZ1FWalt - KZ1F Member
    edited November 2016
    Guy, I recall that it is called Artificial Ground.
  • DrTeethDrTeeth Member ✭✭
    edited August 2016
    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".
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited June 2016
    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 theis Community and several people have reported success with it.
  • DrTeethDrTeeth Member ✭✭
    edited May 16
    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.
  • VaristorVaristor Member
    edited June 2016
    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?
  • Mike va3mwMike va3mw Member ✭✭
    edited June 2016
    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.
  • VaristorVaristor Member
    edited June 2016
    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.
  • Steve G1XOWSteve G1XOW Member
    edited July 2016
    Guy, the number of turns is way more important than the number of cores! Aim for 8-10 turns each end. 
  • WA2SQQWA2SQQ Member ✭✭
    edited June 2016

    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.



  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited June 2016
    Reactance varies with the square of the number of turns. So more turns the higher the reactants
  • DrTeethDrTeeth Member ✭✭
    edited August 2016
    @ 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.
  • VaristorVaristor Member
    edited June 2016
    Try fixing the root cause. Fix your antennas.
  • DrTeethDrTeeth Member ✭✭
    edited August 2016
    @ 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.
  • Joe WD5YJoe WD5Y Member
    edited June 2016
    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
  • VaristorVaristor Member
    edited June 2016
    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.
  • DrTeethDrTeeth Member ✭✭
    edited August 2016
    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.
  • DraxDrax Member
    edited June 2016
    That's too few ferrites to do anything on HF frequencies.  You would need like 100 of those kind.
  • VaristorVaristor Member
    edited June 2016
    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.
  • WA2SQQWA2SQQ Member ✭✭
    edited June 2016
    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.
    
  • DrTeethDrTeeth Member ✭✭
    edited August 2016
    @ 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.
  • WA2SQQWA2SQQ Member ✭✭
    edited June 2016
    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 **** any RF physically getting into the PC.
  • DrTeethDrTeeth Member ✭✭
    edited August 2016
    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?
  • George Molnar, KF2TGeorge Molnar, KF2T Member ✭✭✭
    edited December 2016

    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.

  • DrTeethDrTeeth Member ✭✭
    edited August 2016
    @ 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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