1. You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
    Dismiss Notice
Dismiss Notice
This forum does not allow a single user to have more than one username. If anyone wants to change their username contact an admin and it will be done. Multiple accounts belonging to the same member will be deleted without warning.

End-fed Halfwave Matching Transformer

Discussion in 'Home Brew' started by DTB Radio, Sep 24, 2020.

  1. HomerBB

    HomerBB Sr. Member

    Joined:
    Jan 4, 2009
    Messages:
    3,743
    Likes Received:
    2,080
    Good for you!
    Gonna go at it with a vengeance.
    I've tried a few before, but only got "close".
    The test response from this one has been the best, yet. As weather fairs and opportunity presents I'll get it done.
    BTW, what is your most used antenna setup for SOTA?


     

  2. binrat

    binrat WDX Club Coordinator
    Staff Member

    Joined:
    Nov 5, 2008
    Messages:
    2,505
    Likes Received:
    1,348
    Homer,
    For SOTA, it is about 60/40 EFHW / dipole.
    I am fortunate to have many of the summits with a trees or at least a few bushes. EFHW work well in an inverted V configurations, ends held up with hiking poles and the center via a crappy fishing pole.
    I plan to finish today another EFHW that will weigh a few ounces for 20 metres and is mounted on a male bnc connector.
    If I get bored today I will post some pictures of various transformers.
     
  3. binrat

    binrat WDX Club Coordinator
    Staff Member

    Joined:
    Nov 5, 2008
    Messages:
    2,505
    Likes Received:
    1,348
    20210219_120254.jpg Well my latest 20 metre efhw is done. Toroid is a Fairrite # 2643625002 wrapped with #24 wire 49:1 ratio, mounted on a BNC. Wire element is #26 poly stealth wire.
    SWR was 1.09:1 at 14.160.
     
    AudioShockwav and HomerBB like this.
  4. HomerBB

    HomerBB Sr. Member

    Joined:
    Jan 4, 2009
    Messages:
    3,743
    Likes Received:
    2,080
    Awesome.
     
  5. magnuman

    magnuman Well-Known Member

    Joined:
    Feb 20, 2010
    Messages:
    200
    Likes Received:
    150
    Hey Homer,
    Just wondering..in your picture you have the earth of the coax connector connected to turn 2 of the coil and the center to turn 0. I have always put the center of the coax to turn 2 or 3 of the coil and the ground at 0.
    Probably makes no difference but thought I would mention it.
     
  6. HomerBB

    HomerBB Sr. Member

    Joined:
    Jan 4, 2009
    Messages:
    3,743
    Likes Received:
    2,080
    You, my friend, are only the second person to notice this, and bring my attention to it.
    I have corrected it taking reversing my mistake. I have made them correctly, but ... my fallibility ...
    As good as the SWR was before, it is now slightly better on the work bench. I have yet to test it with a wire. Soon.
     
  7. magnuman

    magnuman Well-Known Member

    Joined:
    Feb 20, 2010
    Messages:
    200
    Likes Received:
    150
    You are welcome Homer...
    I think you like experimenting so when you wind the secondary leave about 6 inches of wire on the end after the coil. In the field especially for SOTA stuff we don't always get to set up the antenna the way we would like. Having the ability to add or remove a winding on the secondary can bring the antenna into perfect tune for max performance on any one band. The height above ground of the transformer and its proximity to anything conductive also affects the SWR. I don't run any grounds or counterpoise from the unun but I do place a choke in the coax line, 0.05 wavelengths for the lowest band in use down from the unun.
    These end fed half wave antennas using the 49:1 unun transformers are the easiest and most practical antennas out there. And they work well. Single band or multiband. You should not need a tuner at all.
    My vertical 40m version on a 60 ft push up fibreglass pole works awesome.
    No ground plane to worry about.
     
    HomerBB likes this.
  8. HomerBB

    HomerBB Sr. Member

    Joined:
    Jan 4, 2009
    Messages:
    3,743
    Likes Received:
    2,080
    I am looking forward to getting one to work "no tuner". To date, each I've tried has been "close", but never tuner free.
    I've been running a random endfed on the base as I was using a tuner anyway.
    Given your advice about winding, or unwinding a wrap of wire from the toroid for fine tuning a band, what prohibits adding a wrap or two, then putting tap points across the last five wraps for a quick change setup?
    Your thoughts...? Anyone...?
    I am going to do it and see.
     
  9. binrat

    binrat WDX Club Coordinator
    Staff Member

    Joined:
    Nov 5, 2008
    Messages:
    2,505
    Likes Received:
    1,348
    I noticed but thought it was by design. My small ones you need to do that due to the limited working space in there.
    I have never had a good wide scan with a resistor inserted in leu of wire. I add wire for 40 metres, tune it to the best swr by adding or removing turns off of the toroid, then tune the wire to the part of the band I want. Then check other bands (20,15,10) and add the compensating coil about 72"-74" from the transformer and tune the coil. It seems to work for me.
     
    HomerBB likes this.
  10. HomerBB

    HomerBB Sr. Member

    Joined:
    Jan 4, 2009
    Messages:
    3,743
    Likes Received:
    2,080
    @binrat
    The resistor thing is just to "ballpark" the transformer for me. All of them I've made that passed the resistor test failed the wire test. This time I will take more time and use the methods you guys are providing to get where I need to be.
     
  11. magnuman

    magnuman Well-Known Member

    Joined:
    Feb 20, 2010
    Messages:
    200
    Likes Received:
    150
    I did see something about that on the net and also using a variable capacitor across the input. I tend to add or remove turns when tuning for lowest SWR in a single band EFHW.
    I have used the following criteria when using end fed antennas.
    Please take into account that anything conductive nearby the antenna will serve to detune or tune the antenna to a certain degree. They really need to be in the clear. Raising and lowering the transformer above ground will affect your SWR readings. For best results try to get the transformer in the clear and 4m or so above ground.
    For 80m to 10m use a 49:1 ratio and you will be in the ballpark. For 160m and 80m only, you can try a 64:1 ratio which has 3 turns on the primary and 24 on the secondary.
    The outer shield of the coax is part of the antenna system (whether we want to admit it or not.) For half wave end fed antennas it is said that 0.05 wavelengths of counterpoise is enough. So I always place a choke 0.05 wavelengths in the coax down from the transformer for the lowest band in use. That works wonders to keep RF out of the shack and really makes tuning a lot easier. I have not tried grounding the transformer. People have said it helps performance.
    Tune it to 14.2mhz by adjusting the wire length.
    To bring in 10 and 15m add the 6 turns on 1" a diameter former in the antenna wire, about 2m from the Transformer.
    How you lay out the antenna also determines it's effectiveness. Sloping or vertical or inverted V works well.
    Its a half wave multiband antenna. CBers and Hams have been using them with great effect on 11 and 10m for years. they work great on the other bands too!
     
    binrat likes this.

Share This Page

  • About Us

    The WorldwideDX Radio Forum was originally established in 2001. We pride ourselves on welcoming Radio Hobby enthusiasts of all types, while offering unbiased, informative, and friendly discussion among the members. We are working every day to make sure our community is the best Radio Hobbyist's site.
  • Like us on Facebook

  • Premium VIP Member

    The management works very hard to make sure the community is running the best software, best designs, and all the other bells and whistles. Care to buy us a beer? We'd really appreciate it!

    Donate to us!