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Balanced Feedline Balun recommendation for T matching network

Discussion in '"Boat Anchor" & Classic Equipment' started by K8SQB, Sep 2, 2019.

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  1. K8SQB

    K8SQB Ham Member QRZ Page

    Johnson Matchboxes are nice because they include a balun for hooking up directly to window line, but I have a tuner which does not include that feature. I'll probably never run over 200 watts (never say never, right, right) but the manufacture, like E. F. Johnson is now a thing of memory.

    So, in the event I find myself wishing to hook up a balanced feedline the formerly optional balun available with the tuner isn't in my possession and probably never will be (probably scarce as hens teeth)

    I have some Fair Rite #31 mix 2 inch OD cores and some 12 AWG magnet wire here, how would I go about winding a good balun I could take with me in my kit?
     
  2. K5UJ

    K5UJ Ham Member QRZ Page

    If you mean some kind of ferrite core transformer, they never had that, but the link and coil as designed are an unbalanced to balanced transformer.
    No they're not. I see them at hamfests all the time.

    This isn't the answer you are looking for, but you'll be much better off buying and using a Matchbox with your balanced line instead of fooling around with a T network and typical ferrite core transformer.
     
    N2EY, K4KYV and KS4W like this.
  3. K4KYV

    K4KYV Subscriber QRZ Page

    If you already have the T-network tuner, try inserting a 1:1 balun between the rig and the tuner. Mount the tuner on stand-offs or some other insulating material, leaving the whole thing, case and all, floating above ground. Be careful when adjusting the knobs on the tuner, since the case may be hot with RF.

    This way, the balun is working into a matched load with minimal reactance near its nominal load impedance, while the floating T- or L- network is able to serve as a balanced output. An in-line balun is inherently designed to work into a specific load impedance that is primarily resistive with little or no reactive component. Depending on the antenna configuration, the window line may present a highly reactive load far removed from the nominal load the balun was designed to work into. This may result in excessive RF loss in the ferrite core transformer, possibly causing it to run hot. The ferrite core may be driven to saturation on peaks when operating far from its nominal impedance, and this can drive it into nonlinearity, generating harmonic and spurious sideband products.
     
  4. W5LZ

    W5LZ Ham Member QRZ Page

    The way 'KYV' put it is one of the better ways of looking at/understanding a balun's use. They really don't work from day light to dark, they are for specific frequency ranges. It isn't too smart to prepare for something that typically isn't very likely to happen. Sure, keep that possibility in mind, but don't let it 'control' you. The two 'mainest' reasons you see used baluns for sale are 1) they were too 'small', and 2) just weren't needed in the seller's particular circumstances. There are other reasons but those are the two 'mainest' ones.

    Disclaimer: Am I an authority on baluns? Yes! ... and I got this huge boat tied up in California for sale and you really need it! <-- sarcasm, if you hadn't figured it out.
     
  5. AH7I

    AH7I Ham Member QRZ Page

    I use 11 or maybe 12 turns of 72 ohm twin lead, 2 x 31 core, for 80 and 40.
     
  6. WA9UAA

    WA9UAA Ham Member QRZ Page

    A 1:1 balun ratio is better in case you run into an impedance under 50 ohms. A 1:1 balun will also have almost zero loss because it only reacts to currents on the outside of the coax ie. keeping the system balanced.
    73,
    Rob
     

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