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EFHW that weighs 2.7oz for QRP SOTA Activations

Discussion in 'Amateur Radio News' started by KK6USY, Mar 25, 2021.

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  1. KK6USY

    KK6USY Ham Member QRZ Page

    Not sure if anyone has ever done an antenna this way before , I just wanted to share this easy to build End Fed Half Wave Antenna with everyone. I hope you enjoy the build and make one for you own use!

    KN4OZH, K5MPH, WA7OZT and 17 others like this.
  2. KM1NDY

    KM1NDY Ham Member QRZ Page

    Watched your build. It is a really cool design that I may borrow. Thanks for sharing it!

    I recently made this 49:1 transformer using two 240-43 toroids for qro (I have a detailed blog post on it too.)

    My question is how did you (or anyone else) decide what size/type toroid and wire gauge to use for their antenna projects? Is there some secret handy reference chart available? A guess? Prior knowledge of such things?

    It seems like a ham impedence transformer parts cheat sheet for homebrewed antennas (toroid size, toroid type, winding pattern, expected impedence ratio) must exist somewhere. Where have I not been looking? Or is this such a basic ingrained part of electronics that everyone whose studied electricity knows it off the tops of their head?

    I too want to be able to readily scale the size of my antenna builds based on tx power, but short of copying someone else's design or trial/error, am unsure how to proceed. I'm interested in comments on this.

    KF4ZKU and KK6USY like this.
  3. KK6USY

    KK6USY Ham Member QRZ Page

    First let me say cool call sign, Mindy! I usually just google what I want to make , look at a few designs for what is used to make the transformer. A lot of what is out there is from trial and error of Hams over the years, antennas haven't changed much just how they are constructed. This antenna was from me checking out Dan's web site and thinking, I think I know a easier way to construct that antenna. I do use a different approach than he did with the Z type 49:1. Dan and I chatted and why he went with a different wind was because of not being able to get the antenna high enough and using a QRP transceiver that didn't have a tuner, I use a KX2 and that isn't a problem for me. I don't know of any chart that spells everything out but if you go on sites that sell the toroid's not amazon they have spec sheets that tell frequencies that toroid will cover. I hope this helps, You can email if you need help with something and if I don't know I will try to find out for you through some Hams that I know.

    73 Chuck
    KF4ZKU and KM1NDY like this.
  4. KM1NDY

    KM1NDY Ham Member QRZ Page

    Thanks Chuck!
    Pretty much sums up how I have been tackling transformers too. I appreciate your offer too. It is a really neat design... I'll let you know if I build one!
    KK6USY likes this.
  5. N1IPU

    N1IPU Premium Subscriber QRZ Page

    Cool design for light weight.
    KF4ZKU and KK6USY like this.
  6. KF8IV

    KF8IV XML Subscriber QRZ Page

    Just found your channel and subscribed. Great video!
    KK6USY likes this.
  7. W2GIW

    W2GIW Ham Member QRZ Page

    Interesting SWR's.....but at what impedance?
  8. K2MIJ

    K2MIJ Ham Member QRZ Page

    I did the same thing with a Random wire End Fed after watching Adam K6ARK's build of a 9:1 unun on a BNC connector, my eyes and fat fingers were just not up to the task with his build so I figured I could do the same on a BNC Binding post adapter, so far it works great for a quick deploy antenna while portable!
    KK6USY, KM1NDY, KI4POT and 2 others like this.
  9. N8TGQ

    N8TGQ Ham Member QRZ Page

    I figured I would add my version to the thread. The matcher isn't the smallest, but I makeup for it with the winder( an old gift card).
    Another thing I've done is tie knots in the wire at the resonant points for 17, 20, 30 and 40 meters. Then just wind the wire out to that point and you're set. No traps or connectors to get caught up where you cant reach.
    Have fun!

    KB0TTL, KO4OUD, KK6ZLF and 5 others like this.
  10. KI4POT

    KI4POT Ham Member QRZ Page

    Thanks for the idea. I bought the components to make K6ARK's version, but could not manage the fine soldering. I can use the same toroid and magnet wire to make the transformer and just mount it to the binding post adapter as you've shown though.

    AJ6KZ and K2MIJ like this.

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