Ultimate Ferrite Solution

Clifton Labs (Jack Smith), which is now defunct, used to offer the Z5100A which is the best thing you can get for cleaning up your coax lines.  Unfortunately, DX Eng is not offering it. If you can find one, great. If you can't, contact me via mail.



  • It consists of 5 ferrite toroids and a length of coax, so you can easily fab one yourself. I have to find a source for one of the cores, then I'll post info on a "kit" 
  • Flag :-)
  • edited May 2017
    Hi James,

    I replied directly but thought it may also be of interest to others.

    This is an interesting design, but I notice that the common mode attenuation figures are quoted as dB in a 50 Ohm system (which is fair enough in itself), however the common mode impedance along a length of feeder could be anything from a few tens of ohms to several K Ohms. So the effectiveness also depends upon where the choke is placed along the coax feed line. 

    E-Probe antennas have a very high feed point impedance and as a result they are particularity prone to the pickup of unwanted noise from common mode currents being carried on the outside of the coaxial connecting cable (which forms part of the antenna).

    One easy way to improve the performance is  to use the choke (or multiple chokes) in conjunction with ground spikes  placed at regular intervals. The combination of high series resistance to the common mode path and a low shunt resistance to ground makes a much more effective filter.

    This link also shows a similar design (but it is optimised for transmitting on the amateur bands) along with some useful background information.


    Martin - G8JNJ
  • I agree with Martin,

    Having a high impedance choke plus "ground" on the unbalanced side helps a lot. There's no such thing as direct RF ground it's more a ground impedance. But if your choke(s) is high-Z enough, it will be like putting a low value resistor at the bottom end of a voltge divider.

    There is no difficulty in buying ferrites for chokes. For receive in particular there's no need to layout lots of cash. Choose from parts on this page:
  • Jack's original article  <-click
  • That was a massive design compared to what I've seen elsewhere, but Jack is/was an RF genius so why not try. I had his active antenna once, and it blew away the Mini-Whip in comparison.

    Bjarne Mjelde
  • All parts except the 40T1417-104 appear to be available. Could there be a substitute/equivalent for the latter?

    Bjarne Mjelde

  • Thanks James, I have ordered enough to make for all my beverages. That said, for a choke to remove noise there actually has to be (internal) noise, and I'm not sure of the internal/external distribution of my noise sources.  Wellbrook made an "isolator" several years ago, which does lower the noise floor 4-5 dB on lower part of MW. I also ordered a miniature "galvanic isolator" from a Japanese HAM recently, it was tested yesterday and had identical performance. Insertion loss 0.5 dB measured by my signal generator. Both were connected just in front of the receiver input. My coax feedlines are up to 300 meters so it could be interesting to experiment a bit.

    Bjarne Mjelde
  • Sorry for the thread necromancy, but does anyone still have the PDF at http://rx.jimlill.com/cmca.pdf? It’s no longer available.
  • edited January 2018
    the missing file is back...

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