EFHW , different ways to wind the toroids

Technical Support and Equipment Antennas
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I like to use the compact portable transformer made by Nathan G5KCI lately , It tunes well on the four bands and performs well too , but I made a 49:1 transformer for the End fed half wave antenna a while ago using the most common method you see on YT etc which has seven turns including the two twisted together primary windings then you cross over to the opposite side to complete the total of fourteen turns . It’s all something to do with dividing the approx 2400 Ohms impedance of the EFHW by 49 to get it somewhere near 50 Ohms but there’s loads of info out there on how they work out the ratio of primary turns to secondary .
I thought I’d try one of the alternative ways to wind the core which some say is better ? So, I took everything to bits used some thicker wire and made the two promary windings , but instead of twisting them I tapped with solder, the 2nd turn with a single bit of wire to connect to the centre conductor on the SO239 then wound the other 12 windings close together up one side of the core .
The VNA showed nice low SWR on 40, 20, 15 , and this time on 10m as well which I found on others I made 10m was always in tune a bit too far up the band above 29MHz needing the AMU anything below that . I tried it on Binsey yesterday with some good contacts on the bands I tried , but whether it was any better than it was is hard to gauge , it worked well on the day but , I suppose in the real world propagation probably has more influence on results than any of my tinkerings will ever have ?
Richard

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The Yaesu cap keeping the hot sun off my neck was kindly donated by Len M0SKY
These caps are very expensive I believe , but he does get a free radio with every one !

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HAHA Len must have 50 caps by now. Looks good Richard, good info too.
I Ran your original text into Ai and this is what it came up with Richard… Scary …

:wrench: Purpose

Build a 49:1 impedance transformer to match a high-impedance (~2400Ω) EFHW antenna to a 50Ω coaxial feed (like from your radio).

:toolbox: Materials Needed

  • Toroid core (e.g., FT240-43 or FT140-43 commonly used)
  • Enamelled copper wire (around 1mm or 18 AWG for less loss)
  • SO-239 socket (or BNC)
  • Enclosure
  • Optional: VNA for testing SWR

:repeat_button: Transformer Winding (49:1 Unun)

There are two versions mentioned:

:pushpin: Original (Common YT-style method):

  1. Twist two wires together (these form the primary, which is 2 turns).
  2. Wind 7 turns total, with the twisted pair.
  3. After 7 turns, remove one wire and continue with the remaining wire for another 7 single turns.
  4. This gives you a 2-turn primary (twisted) and 14-turn secondary. The ratio is:(142)2=49:1\left(\frac{14}{2}\right)^2 = 49:1(214​)2=49:1

:pushpin: Modified Version (Richard’s method):

  1. Use thicker wire (better power handling, lower loss).
  2. Make 2 primary turns, but instead of twisting, solder-tap a connection at the second turn (where the center conductor of the coax will go).
  3. Wind 12 close-spaced turns (secondary) on one side of the toroid (no crossover as in traditional style).
  4. Connect:
  • Start of primary to ground side of SO-239.
  • Tapped solder point (2nd turn) to center pin of SO-239.
  • End of 12 turns to the antenna wire.

This layout still maintains the 2-turn primary and 14-turn secondary, but done more cleanly or differently.

:satellite_antenna: Antenna Type

  • End Fed Half Wave (EFHW): Wire length for common bands:
    • 40m: ~20.3 meters
    • 20m: ~10.1 meters
    • 15m: ~6.7 meters
    • 10m: ~5 meters
  • Use a 1m counterpoise or connect to coax shield.
  • Requires no tuner on most bands when properly matched.

:microscope: Performance Notes

  • Richard noticed that 10m was usually tuned too high (e.g., 29 MHz) with older windings, but with his new winding, it now tunes better across the band.
  • Propagation (ionosphere conditions) affects results more than tiny tweaks in transformer construction.
  • A VNA (Vector Network Analyzer) was used to verify SWR dips across bands.

:chart_increasing: Summary – How to Build It

  1. Take a toroid core (e.g., FT240-43).
  2. Wind 2 turns for primary, tap the 2nd turn for SO-239 center.
  3. Wind 12 more turns with a single wire on one side of the core.
  4. Connect:
  • Ground side of SO-239 to start of primary.
  • Center of SO-239 to tap on 2nd turn.
  • End of 14-turn wire (after secondary) to antenna wire.
  1. Test with VNA for SWR on 40, 20, 15, and 10 meters.
  2. Mount inside a weatherproof box.

ai Diagram :slight_smile:

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p.S i dont know how accurate all of that is and the diagram lol

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The text seems fairly cobsistant with what I’ve read Lee . The diagram is a bit confusing The plans I’ve used have the tap going to the centre pin of the so239 and the other bit to the outer shield and counterpoise . This video describes it well except it uses the cross over instead of winding all the coils together up one side . https://www.youtube.com/watch?v=mVlFHi2qpWo&t=325s
Did AI work out how many caps Len has as well ? :grinning_face_with_smiling_eyes:

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Ai knows Len as many caps hahahaha