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Author Topic: Making Your Own Un-Un or Baulun  (Read 495 times)

K1KIM

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Making Your Own Un-Un or Baulun
« on: October 24, 2022, 10:19:41 AM »

When winding your ferrite cores do you wrap them in teflon tape before winding with either enameled 16 AWG wire and then again on top of the wire to hold it in position?

Or do you use PTFE coated wire over a bare core? PTFE wire has gotten ridiculously expensive it seems.
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W9IQ

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Re: Making Your Own Un-Un or Baulun
« Reply #1 on: October 24, 2022, 10:32:58 AM »

When winding your ferrite cores do you wrap them in teflon tape before winding with either enameled 16 AWG wire and then again on top of the wire to hold it in position?

Or do you use PTFE coated wire over a bare core? PTFE wire has gotten ridiculously expensive it seems.

If you are making an autotransformer (unun), I recommend against covering the core with anything. Most of the common designs are marginal from a heat perspective to begin with and another layer only increases the thermal resistance. I always use silver plated PTFE wire. I buy shorter lengths from Nebraska Surplus Sales if I don't have what I need in stock and I don't want to buy a full spool. Remember, the gauge of wire can be quite small - I am often winding with 18 or 20 gauge wire for the primary and secondary turns.

- Glenn W9IQ
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God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W4NBO

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Re: Making Your Own Un-Un or Baulun
« Reply #2 on: October 24, 2022, 10:46:02 AM »

I just built a 9:1 unun for a end fed to a tree about 60' high with 5 radials. Works great. Comparing it to my 130' doublet and 6BTV with 32 radials. The end fed is a bit quieter probably due to its distance from 7.2kv lines along one side of my yard as compared to the other antennas. I used scrap wire from ballasts. They are thin vinyl coated wires about 18 gauge.

As to enamel coating, lots of cores, transformers, etc wrapped with just the enamel coating as insulation but I can understand the caution of possibly the enamel coming off if that is your concern. As far as keeping the wire in place, I used zip ties.

73 Chuck
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DL9BDM

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Re: Making Your Own Un-Un or Baulun
« Reply #3 on: October 24, 2022, 11:41:42 AM »

When you use enameled wire, it can't hurt to surround the ferrite cores with a layer of plumbers tape (PTFE), especially if they are sharp-edged.
« Last Edit: October 24, 2022, 11:51:15 AM by DL9BDM »
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K1KIM

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Re: Making Your Own Un-Un or Baulun
« Reply #4 on: October 24, 2022, 11:47:52 AM »

When winding your ferrite cores do you wrap them in teflon tape before winding with either enameled 16 AWG wire and then again on top of the wire to hold it in position?

Or do you use PTFE coated wire over a bare core? PTFE wire has gotten ridiculously expensive it seems.

If you are making an autotransformer (unun), I recommend against covering the core with anything. Most of the common designs are marginal from a heat perspective to begin with and another layer only increases the thermal resistance. I always use silver plated PTFE wire. I buy shorter lengths from Nebraska Surplus Sales if I don't have what I need in stock and I don't want to buy a full spool. Remember, the gauge of wire can be quite small - I am often winding with 18 or 20 gauge wire for the primary and secondary turns.

- Glenn W9IQ

Will the 18 gauge be sufficient for 1 kw voice? Solid or stranded?
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W9IQ

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Re: Making Your Own Un-Un or Baulun
« Reply #5 on: October 24, 2022, 12:04:39 PM »

Yes, 18 gauge is sufficient for 1 kW CW or voice SSB - you can use larger if you prefer or have it available. If you are using FT8 at 1 kW, I recommend 16 AWG or larger.

I use stranded but solid would help keep it formed around the toroid. Small cable ties help hold things in place as the PTFE insulation is slippery.

- Glenn W9IQ
« Last Edit: October 24, 2022, 12:13:03 PM by W9IQ »
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God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KD6VXI

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Re: Making Your Own Un-Un or Baulun
« Reply #6 on: October 25, 2022, 04:49:50 AM »

I found that things like Sally Hansen's "Hard As Nails" (for womens fingernails) get the windings to sit pretty.

(edit)  I use drops 'here and there' to hold the windings in place.  Not a bunch, just enough.  In just enough spots.  Drops.

I use teflon wire. 

I don't tape the ferrite.  Great way to trap heat.  Heat = cracking.

--Shane
WP2ASS / ex KD6VXI
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KU3X

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Re: Making Your Own Un-Un or Baulun
« Reply #7 on: October 25, 2022, 06:15:35 AM »

I've been making all values of UnUn's for almost 30 years. If they are for a primary station, I use an FT 240-XX core. I have never ever covered any core with any material, they are always bare cores. I always use #16 enamel wire and run legal limit through them. The last few I built were for inverted L's. They were 22.22 ohms to 50 ohms. They were for a friend's contest station. He ran 1500 watts RTTY in contest conditions into them and they never failed......and.....they never every got warm to the touch.
For mobile, I usually use an FT 140-XX core and either use #20 or #18 enamel wire, depending on how many turns I have to fit on the core.
I have never had an UnUn fail. 
UnUn's for end fed antennas are a different story. I put them in a different category.

Here's a great book for building Unun's.

http://www.introni.it/pdf/Amidon%20-%20Transmission%20Line%20Transformers%20Handbook.pdf

Disclaimer: This post is for general information for everybody, not just one person. I hope this avoids any nit picking for this post.

Barry, KU3X
« Last Edit: October 25, 2022, 06:20:41 AM by KU3X »
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K1KIM

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Re: Making Your Own Un-Un or Baulun
« Reply #8 on: October 25, 2022, 06:35:28 AM »

I've been making all values of UnUn's for almost 30 years. If they are for a primary station, I use an FT 240-XX core. I have never ever covered any core with any material, they are always bare cores. I always use #16 enamel wire and run legal limit through them. The last few I built were for inverted L's. They were 22.22 ohms to 50 ohms. They were for a friend's contest station. He ran 1500 watts RTTY in contest conditions into them and they never failed......and.....they never every got warm to the touch.
For mobile, I usually use an FT 140-XX core and either use #20 or #18 enamel wire, depending on how many turns I have to fit on the core.
I have never had an UnUn fail. 
UnUn's for end fed antennas are a different story. I put them in a different category.

Here's a great book for building Unun's.

http://www.introni.it/pdf/Amidon%20-%20Transmission%20Line%20Transformers%20Handbook.pdf

Disclaimer: This post is for general information for everybody, not just one person. I hope this avoids any nit picking for this post.

Barry, KU3X

Strange he does not have a 49:1 transformer listed.
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W1VT

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Re: Making Your Own Un-Un or Baulun
« Reply #9 on: October 25, 2022, 07:07:49 AM »

Jerry stopped doing research in the mid 1990s, perhaps earlier, when he retired and no longer had access to the test equipment he  used to measure his devices.

http://www.arrl.org/news/jerry-sevick-w2fmi-sk
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W9IQ

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Re: Making Your Own Un-Un or Baulun
« Reply #10 on: October 25, 2022, 07:48:55 AM »

Strange he does not have a 49:1 transformer listed.

You should view the book from a historical perspective. The primary application for the 1:49 transformer is the EFHW. These were hardly a topic in Jerry's time. Today, most of his ferrite recommendations are now out of date - there are better ferrites available. The book also contains errors and unresolved observations. Proceed cautiously.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W1VT

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Re: Making Your Own Un-Un or Baulun
« Reply #11 on: October 25, 2022, 08:06:11 AM »

When Jerry was doing his research I had a box full of air variable capacitors, including a few that would handle the high voltage found in the plate circuit of an amplifier.  Back then I used end fed half wave verticals and L network matching networks that used air variable capacitors.  I didn't consider that the capacitors I was using wouldn't be easily available twenty years later.
« Last Edit: October 25, 2022, 08:15:45 AM by W1VT »
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KU3X

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Re: Making Your Own Un-Un or Baulun
« Reply #12 on: October 26, 2022, 05:03:29 AM »

I didn't consider that the capacitors I was using wouldn't be easily available twenty years later.

The last time I was at the Dayton Hamfest, and it was in Dayton at that time, in the tailgater section of the hamfest, I could not find one door knob capacitor or HV plate transformer. It's not like the old days when you could find almost anything for building ham projects. I miss those types of hamfests.

Barry, KU3X
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KD6VXI

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Re: Making Your Own Un-Un or Baulun
« Reply #13 on: October 27, 2022, 12:37:59 PM »

When I fill my sea train next (hopefully) February, I will be selling a LOT of caps.  Vacuum, butterfly, standard air variables, door knobs.  There will also be tubes, amps, transformers, etc.  But I do have a fairly large stash of caps.

I have stuff in stock up to 50Kv.

No amplifiers to build here on the island when you are one of a handful of full time hams here.  I'm sure I'll regret it, but I can't justify bringing 20K lbs of electronics here......  That will end up in the landfill when I'm dirt.

--Shane
WP2ASS / ex KD6VXI
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