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Ham Radio - An end fed half wave antenna with built in counterpoise. (Experimental)

Discussion in 'Amateur Radio News' started by KB7TBT, Aug 28, 2019.

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  1. KB7TBT

    KB7TBT Ham Member QRZ Page

    Ham Radio - An end fed half wave antenna with built in counterpoise. (Experimental)

     
    N9DWE likes this.
  2. W9ZD

    W9ZD Premium Subscriber QRZ Page

    Are you sure that the coax shield is not the counterpoise?
     
    VA7JMP and K3RW like this.
  3. W1YW

    W1YW Ham Member QRZ Page

    The coax WILL radiate. But---if choked properly the counterpoise does a phase cancellation on that electrical length, kinda like a J pole.

    Basically this is a method to end-feed the antenna, normally not easy because the voltage max lies at the ends, and matching it is lossy and not easy. Here the 'end' is really an OCD point electrically. The antenna is designed as a convenience to stop the drooping coax such as you see on a dipole.

    These designs have been around for a while. Nice to see it discussed here.
     
    KK5R and KQ6XA like this.
  4. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    how do you get a 49:1 match?? how much po
    How do you get a 49:1 match to take much power, will how much power will it take? I'm inpresed it will take 40 watts
    I run QRO
     
    AF4RK, KQ6XA and W1YW like this.
  5. K6GB

    K6GB XML Subscriber QRZ Page

    Version of that in an RSGB antenna book 50' long with 25' counterpoise made with speaker wire and a toroid wrapped at the end, the speakerwire goes straight into a tuner, covers 40-10, a half size covers 20-6. They show it as a vertical and it has pretty low radiation angle, they also show a dual phased array, quick and dirty, a roll of speaker wire 2 toroids and a balun.
     
    KK5R and W1YW like this.
  6. W7QQQ

    W7QQQ Ham Member QRZ Page

    Match with an LC resonant tank circuit between antenna and counterpoise. Couple the coax feed with a one or two turn link to L.
    Very efficient.
     
    MM0XXW and K0UO like this.
  7. K0UO

    K0UO Platinum Subscriber Platinum Subscriber QRZ Page

    Just Hit that 49:1 setup made of small speaker wire and a small toroid with 1.5 kilowatts and see what happens !!!!
     
    KQ6XA likes this.
  8. K6GB

    K6GB XML Subscriber QRZ Page

    Better be a big donut and very thick wire, hi!
     
    K0UO likes this.
  9. K6GB

    K6GB XML Subscriber QRZ Page

    Design attributed to K9ESE, phased version to M3KXZ. The book is RSGB Successful Wire Antennas.
     
    KK5R and W1YW like this.
  10. W7QQQ

    W7QQQ Ham Member QRZ Page

    For QRO, I've put 1.5 KW into the matching network I described above. No problem. Use air wound coil and capacitor with sufficient spacing.
    You can make the one or two turn link with a variable capacitor in series so you don't have to vary the spacing of the link coil.
    1 to 1 swr.
    The counterpoise doesn't have to be fancy twin lead... just hang or lay out a few feet of wire... 3 or 4 ft.
     
    KK5R likes this.
  11. KF4ZGZ

    KF4ZGZ Ham Member QRZ Page

    That's nothing more than a (slight) variation of the W3EDP antenna. Kind of a "W3EDP Jr."
    I have seen this design before also, but with a 4:1 balun.
    A 4:1 balun would probably work much better.


    The whole thing is not similar to a zepp it is a short zepp.

    I do think the coax is doing more than you think as a counterpoise ... i don't see 4ft. doing it on 80m.

    I see the "dipole-similar" bandwidth as a function of loss in the 49:1 balun.
    I would like to see you build a 4:1 and do a comparison ..... and may try different counterpoise lengths.
     
  12. KF4ZGZ

    KF4ZGZ Ham Member QRZ Page

    [​IMG]
     
    W4HM, N4GST, K0UO and 1 other person like this.
  13. W1YW

    W1YW Ham Member QRZ Page

    This is an OCD. No other description applies:)

    The coax was not designed to be part of the antenna, but will radiate unless choked, for example with two or more ferrite collars.

    The only advantage of this antenna is that it is physically end-fed.

    The feedpoint is placed to capture a portion appoaching the current max where the impedance is not several thousand ohms. The tradeoff is how far you 'fold it back' versus what impedance you want to tap into. Again, that fold-back acts like a transmission line that phase cancels. If its too long you will lose gain in the far field from the phase cancellation.

    I would never design for a balun beyond, say, 9:1 myself...
     
    K0UO likes this.
  14. WG7X

    WG7X Platinum Subscriber Platinum Subscriber QRZ Page

    THIS!

    Thanks for pointing that out. Just goes to show that there is sometimes nothing new under the sun, just variations on a theme. I wonder if the OP has ever read any of the copious reams of material in any of the antenna how-to or theory books that are around?

    ARRL, RSGB: two great sources of antenna manuals both theoretical and real life.
     
    Last edited: Sep 1, 2019
  15. WN1MB

    WN1MB Ham Member QRZ Page

    If he ever does, you'll be sure to know: he'll post a YouTube video showing him reading books. ;)
     
    WG7X likes this.

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