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Is this a Current Balun or a Voltage Balun?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by 2E0CIT, Feb 28, 2019.

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  1. VK4XJB

    VK4XJB Ham Member QRZ Page

    When I started that is what people used. That what people would tell you to use. The balun kits at the time contained a T200-2 (powered iron core) with enough wire and instructions to wind a trifilar 1:1. So using a 1:1 voltage balun was it. Then from that when I wanted a 4:1 it was still voltage balun because it was what pushed as the type of balun to use.

    At the moment the 2 baluns I am the happiest with are the 1:1 current balun currently on the inside end of my ladder line and a 2 core current balun for the rare times 4:1 is the ratio I need.
  2. WR2E

    WR2E Ham Member QRZ Page

    Not sure if anyone has touched on this directly or not... didn't re-read the whole thread, but here's my somewhat simplistic take:

    A VOLTAGE balun will force equal voltage. The CURRENT will be whatever it needs to be to force that voltage. If the load is not perfectly balanced, the currents will be unequal. If the currents are unequal you will have current flowing on the outside of the feedline. If you have current flowing on the feedline, it will radiate.

    A CURRENT balun will force equal current regardless of the balance of the load. The VOLTAGE will be whatever it needs to be in order to force that current. If the currents are equal, there will be minimal current flowing on the outside of the feedline. A difference of voltage between the elements is relatively inconsequential.

    In general, and I think this may have been stated, use a VOLTAGE balun when you need to do impedance transformation, and a CURRENT balun when you want to choke common mode current flow.

    There IS a form of current balun that will transform impedance that requires TWO cores.

    When you need impedance transformation AND current balancing, there are HYBRID balun designs that can achieve this.
    WD4ELG likes this.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    Last edited: Aug 4, 2020
  4. WA7ARK

    WA7ARK Ham Member QRZ Page

    This statement refers to the effect resulting from using a multi-winding transformer where the windings are connected to each other, otherwise called an "autotransformer". An example would be the "center-tapped" (two) winding "4:1 balun" as depicted in this partial tuner schematic:

    Your statement does not describe the effect of using a 1:1 transformer such as I showed at the middle of my hand drawing in post #27. Because I chose to draw two isolated windings with four external terminals, making a true transformer (not an autotransformer) there is zero CM (I3=0) and I4 = I5 (see GM3SEK's diagram in my post #27).

    The isolated winding transformer forces equal currents (I4 = I5) just like the Current Mode devices I show... It is only when you interconnect the windings that those currents can become unequal because now there is a new path for I3 (now I4 = I5 - I3).

    The isolated-winding transformer is frequently used to block CM in receive applications, where core losses and heating do not matter. It can be 1:1 or 10:1 or 1:10 or almost any Z ratio you want... If it is used to transmit, then all of transmit power is transferred to the load via flux linkage. In the 4:1 auto-transformer connection shown in the tuner above, only one half of the transmit power is transferred to the load via flux linkage; the other half goes directly to the load..., but that is a consequence of it being 1:4; with a 1:1 voltage balun, the core transfers 100% of the power...
    Last edited: Aug 4, 2020
  5. WR2E

    WR2E Ham Member QRZ Page

    No, that's why I called it a 'simplistic view'. The 'basics' as it were, for the folks that need a simple explanation of which to use, and why they might make that choice.

    You didn't note any inaccuracies in my post, did you? If so, please note them.

    I leave the textbook stuff up to fellas such as yourself, which you are good at.

    I'm good at 'simple'.
    Last edited: Aug 4, 2020
  6. AA4BQ

    AA4BQ Ham Member QRZ Page

    I'm not sure if sharing this here is helpful but this thread has been very essential to my efforts here and I really appreciate all terrific content of this thread. I wasn't happy with my BT-1500A and had put my Johnson Matchbox back in line (which demonstrated a better balanced output). But, finally this mod eliminated the balance issues I was having with the BT-1500A and performance is as balanced as the JMB. And, now ALL the bands tune really easily. I use a full-wave 80M loop so I didn't try 160m obviously - but other than that. S/N improved as well as elimination of CMC in the shack. Win-win. This took lots of time and many iterations of configurations and core mixes. I tried 43s, 52s, and some others. Without the great advice and encouragement from Gary, K5AMH, I believe I would have been beaten. Here are some photos of the network in place - just in time for the DX going on this weekend. :)




  7. WR2E

    WR2E Ham Member QRZ Page

    Tell us about the design of the balun.

    What mix did you settle on?

    What are the winding details?
  8. KD2PII

    KD2PII Ham Member QRZ Page

    I guess you would call that a balbal.
  9. VK2NZA

    VK2NZA XML Subscriber QRZ Page

    AA4BQ, I have just been having a conversation over at E ham in regard to modifying the Johnson Matchbox for lower impedance, K0ZN, W9IQ and WB6BYu have been very helpful,
    however my point here is in regard to your belief that the Matchbox provides better balance than your Palstar BT-1500A, in fact if i'm not wrong the ARRL guide to Antenna Tuners does some comparisons into a G5RV and includes amongst the tuners the Palstar AT-1500 Bal , the Johnson Kilowatt Matchbox and the 275 Matchbox 'lite" .
    looking at the results indicates that both Johnsons appear to get better balance results than the Palstar however with a somewhat narrower impedance range.
    Although modifiable by altering feedline length or placing a 2:1 Unun at the input as K0ZN has stated in his review allowing lower impedance match on the Johnsons without affecting efficiency much.
    i have a very tidy Matchbox Lite that i intend to incorporate with a 40 meter multiband horizontal loop and it would be my choice also, remembering the small matchbox will easily rum a Kiowatt PEP into reasonable antenna's whereas the Big one will do 3 KW.


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