[CTSARA] PTFE tubing for copper wire used for 49:1 balun

[Steve Dick]

Ilan, I have not seen any problems from anyone, not even once in Steve Ellingtons’s facebook group, when using 500W-1kW using the three core FT240-52s and no teflon tape on the cores or PTFE tubing on the wires.  The secondary turns are pretty separated, and the “crossover” in the middle of the secondary keeps the high voltage output away from the grounded primary side. The bigger problem might be core heating on 80 meters for high duty cycle mode like CW at high power.  SSB -  no problem.  Digital modes – shouldn’t be using high power anyway  

From: Ilan Grosman 
Sent: Monday, December 02, 2019 10:26 PM
To: Steve Dick 
Cc: ctsara Mailman 
Subject: Re: [CTSARA] PTFE tubing for copper wire used for 49:1 balun

Thanks Steve for clarifying. Your deck on the EFHW is the authoritative and best source I am following for materials and the build. I like that you put in not only the how, but the why and list of materials to build. I will be using the 3 52 cores as you suggested, and 12 AWG transformer wire. Also have the capacitor for the transformer (100pF) and in the middle of the antenna another capacitor (330 pF) as Steve Ellington is suggesting in his Facebook group on that type of antenna. 

At this point I am running only 100W but don't want to change configuration when/if I move to higher wattage, and there didn't seem to be a disadvantage to overbuild it from your deck other than cost of 52 versus 43 cores.


Ilan






On Mon, Dec 2, 2019 at 4:33 PM Steve Dick <sbdick at optonline.net> wrote:

  Hi Elan. How much power are you running?  PTFE tubes are probably 
  unnecessary and can do more harm than good when building 49:1 transformers 
  (presumably for use with an end-fed halfwave antenna?)  For 49:1 
  transformers, they will increase leakage inductances and degrade performance 
  on the higher bands, especially on 10 meters.  They are great when you have 
  smaller turns ratio baluns or UNUNs but can be counterproductive with large 
  turns ratio ununs. I have bought a lot of stuff from Balun Designs.  Their 
  1:1 through 9:1 baluns are great construction  and performance with the PTFE 
  tubing. At one time they sold a 49:1 UNUN and stopped selling it, except by 
  special request.  I have two of them, with the PTFE tubing, and VSWR 
  performance at the high end is not very good.   My homebrew UNUNs, which do 
  not use teflon tubes, have better performance at the high end.

  -Steve K1RF

  -----Original Message----- 
  From: Ilan Grosman
  Sent: Monday, December 02, 2019 3:11 PM
  To: ctsara at mailman.qth.net
  Subject: [CTSARA] PTFE tubing for copper wire used for 49:1 balun

  Hi All!

  Any good (cheap) sources you can recommend for getting PTFE tubes to use as
  copper wire sleeves? Building a 49:1 transformer and want to replicate
  balun designs approach.

  Thank you, and see you on Dec 5th.

  Ilan
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