Balanced tuners

Discussion in 'Homebrew and Kit Projects' started by EI6GXB, Sep 13, 2008.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-rl
ad: Left-3
ad: abrind-2
ad: Left-2
ad: L-Geochron
ad: L-MFJ
  1. EI6GXB

    EI6GXB Ham Member QRZ Page

    The RF was (in my case), the feedline coupling into the external speaker wiring (<2" away!! my bad!!).

    Doubt I'll have any RF in the shack from radiation of the antenna, as the plasterboard in the attic is foil-lined! wonder what that'll do for radiation patterns lol

  2. EI6GXB

    EI6GXB Ham Member QRZ Page

    Found some PVC-foam stuff used for replacing balsa wood in models to make the spacers out of - at least it doesn't break when I try to cut notches in it!

    Even if it's not phenomenally successful, it's the experimentation that counts lol.

    Those who have built this tuner - what lead layout works best? Input and output at opposite ends of the board....etc

  3. CT2JUT

    CT2JUT Ham Member QRZ Page

    Beautiful tuner!

    Maybe i stared about 5 minutes looking at the picture.

    I think it belongs to...

    Check here:

    What a really nice job! :)

    73 from Lisbon!

  4. EI6GXB

    EI6GXB Ham Member QRZ Page

    OK, ropey looking, but it's made me a ZS contact so far!!
    I need to cut the base to size and protect the shaft and tidy a little. Even at 100W though, not a tingle from it. There was before I rebuilt it, but the second time I rotozipped the insulation off the copper, and evidently have made a vastly superior connection over jsut scratching it 'off' with a knife. Going on the formula (haven't managed to usurp college's inductance meter!!), handwound coils for ~ 25mH, and the capacitor is a dual-gang Mullard (280pF) from
    I have yet to switch the gangs, so as to give more capacitance (parallel) and less (series), and switch the whole unit itself to input/output, but that will change
    Right now it will tune a 20m dipole to 40m, 30, 18 and 15 all at 1:1.

    Last edited: Oct 7, 2008
  5. W8JI

    W8JI Ham Member QRZ Page

    You know, of course, that you really do not have a balanced tuner? At least not by what is in the picture.

    The idea you can move the balun to the INPUT of a floating network and have a "balanced tuner" is popular, but it is wrong.

    Read this link:

    The tuner in you picture appears to have a single capacitor and two inductors fed from a balun at the input. It is electrically impossible to have a good balanced tuner with that setup. It would be no different at all than just using a normal network with a balun on the output.

    73 Tom
  6. KL7AJ

    KL7AJ Ham Member QRZ Page

    This is why I love my Johnson Matchbox. Now, if someone could make an adjustable link with toroids to make it more compact, we'd really have something. Something like a toroidal tickler coil. I wonder what the topology would be?


  7. KL7AJ

    KL7AJ Ham Member QRZ Page

    It would be TTTT....Toroidal Tickler Topology Technology
  8. EI6GXB

    EI6GXB Ham Member QRZ Page

    Many have used the W2DU balun with great mirth.
    All I did was follow what was set out in the balanced balanced tuner how-to.

    It works. ZS6CCY 4-9. 40, 20, 17 and 15 1:1. No RF in the shack.

    Last edited: Oct 9, 2008
  9. W8JI

    W8JI Ham Member QRZ Page

    I certainly did not mean to imply your antenna would not "work".

    I'm merely pointing out that the only way to build a balanced tuner is to actually build a balanced tuner.

    If you have a network that is not a symmetrical balanced network with a ground reference at midpoint, and you move a balun from the output to the input, you don't do a thing for common mode currents. It doesn't do a thing to improve the effectiveness of the balun.

    You can easily see why that happens at this link:

    This doesn't mean you won't be happy with a less than perfect tuner, or that you have a bad tuner, or that I am picking on your work. It just means we could all do a better job understanding the problem.

    Your circuit may be a correct circuit because there are some that work, but most of them are not correct.

    73 tom
  10. EI6GXB

    EI6GXB Ham Member QRZ Page

    Hmm. Either way, eventually I'll build a single coil Z-match, link coupled tuner, but to find another suitable variable cap :D
Thread Status:
Not open for further replies.

Share This Page