50 ohm unbalanced line to balanced tuner

Discussion in 'Technical' started by K4TQF, Mar 15, 2015.

  1. K4TQF

    K4TQF Member

    Ran across this on the internet... the coil (L3) of coax struck me as an odd way to make the transition from unbalanced 50 ohm to balanced :icon_wtf:

    Never mind the motor driven inductors. If built, I would use a hand crank and cogged belt & pulleys.

    balanced tuner.jpg
  2. W5HRO

    W5HRO Administrator

    It really doesn't do that, it's one of those "Ugly Baluns". Search around the web because there are tons of them. It's just a quick, cheap and shitty way of trying to keep the RF off of your unbalance feedline coming into the shack.
  3. K4TQF

    K4TQF Member

    Looks like some folks are using them... found this in google images

    coax chokes.jpg

    I need to contact that guy and get his take on them.
  4. W5HRO

    W5HRO Administrator

    It's the same thing as using ferrite 1:1 choke baluns at various points on your 50-ohm unbalanced feedline. I personally think the ferrite type work better than the coax type.

    The fact the guy said it's unbalanced to balanced is just BS.
  5. W5HRO

    W5HRO Administrator

    Here, its the same thing as doing the below, but these are better. Unfortunately the guy doesn't make the 4kW models anymore which would handle more power. I still have 2 or 3 of them though. The are just a piece of coax inside with big ferrite beads slipped over it.


    What happens with an unbalanced system using coax is that a lot of RF will often ride along the outside of the coax along the shield like common mode current. The ferrites just absorb and stop it. Those "Ugly Baluns" using wound coax do the same thing just not as well and they in no way create an unbalanced to balance system. If the drawing in your first post was an unbalanced to balanced system then there wouldn't be any need for the "Ugly Balun".
  6. K4TQF

    K4TQF Member

    Yeah, I couldn't see how that coil of coax was going to balance anything. :icon_wtf:

    It may be acting to choke some of that "stray" rf on the shield...
  7. W5HRO

    W5HRO Administrator

    It's forcing instead of matching the unbalanced feed to a balanced output and the "Ugly Balun" is only there to help minimize the RF from getting into the shack during the process. It's just like in your second pic. Those "Ugly Baluns" are there to prevent RFI in the shack.

    To do it right would really require doing the below.

  8. K4TQF

    K4TQF Member

    So, they are in reality "ugly chokes"...
  9. W5HRO

    W5HRO Administrator

    Yeah, just search on the web for "Ugly 1:1 Choke Baluns"

    Those "Ugly Baluns" are ok and better than using nothing at all, but if you really want to do it right just buy some PVC pipe and some end caps and use a 1 ft piece of RG-8U or RG-213 coax inside and select big enough ferrite beads that will slide over it. You just need the right ferrites that have a big enough inside diameter to slide over the coax. No need to wrap any coax around anything. You can just make your own that will handle full AM power with SO-239 connectors on each end.

  10. W5HRO

    W5HRO Administrator

    I found one of my old 4K-LI models (Line Isolator) It's the one the guy doesn't make anymore and good for 4kW PEP.

    Anyway, I used it on my old Desk KW and HB transmitter and it only got just a little warm after long 15 to 20 minute AM buzzard transmissions :mrgreen:

    On the Desk KW I used one between it and the KW Matchbox and then a second one between the KW Matchbox and the antenna. That's back when I was still playing around with crappy coax fed antennas and burning up (shorting) the caps in the 40/80 meter dipole traps :confused:

  11. K4TQF

    K4TQF Member