160m top band inverted L 38mts long should I use it on 80m.

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by 2E0LPL, May 24, 2019.

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  1. WA7ARK

    WA7ARK Ham Member QRZ Page

    How far is the tuner from the "ground stakes"? How long is the wire from of the balun to the ground stakes?

    I agree with 'WIK; if you want to feed the existing Lwire on 80m, get a transformer like this. That will allow use of your existing Lwire on 40m and 20m, likely while bypassing the MFJ tuner. When using 160m, then switch the Lwire direct to the "50 Ohm" Output of the tuner (bypass the built-in balun; it just gets in the way).

    Your Lwire, referenced against earth (if the stakes are close-by and the ground wire from tuner to stakes is less than 2m) will present an impedance of ~45 Ohms at resonance on 160m. That is why the balun is not needed.

    Your Lwire will present a very high impedance at twice its resonant frequency, so that is why you need to switch in the 1:49 transformer.
  2. 2E0LPL

    2E0LPL Ham Member QRZ Page

    The tuner is around 15ft from the ground stake...my shack is on an upper floor.

    The 4-1 balun is incorporated as part of the MFJ tuner.

    The wire indicates resonant at around 1800khz.
  3. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Even with ladder line feed, adding an 80 meter trap somewhere around 1/4 wavelength on 80m will resolve the big problem which is the antenna presenting a very high feed point impedance on 80m where the antenna is very close to half wavelength long.
  4. AI3V

    AI3V Ham Member QRZ Page

    You could possibly make the feedline a quarter wavelength on 80 m, that will transform the high antenna z to a low value at the tx. use a feedline impedance equal or close to the 160m impedance of your antenna to keep from upsetting the 160 tuning.


    Due to the layout of the lot and trees here, I split the difference and use about 90 feet on each side of a doublet.

    Lots of ways to do it.

  5. WA7ARK

    WA7ARK Ham Member QRZ Page

    There is no reason to use the 4-1 balun unless it is useful. Why do you think that using it does anything good?

    In that case, it is the 15ft of ground wire plus the Lwire that resonates at 1800kHz. This is basically a monopole driven against earth. Your feedpoint is 15ft along the monopole instead of being at ground level. I am surprised you do not have lots of RF in the shack?
  6. WB5YUZ

    WB5YUZ Ham Member QRZ Page

    I know OP thinks his antenna is working well on 160m as is, but it would be a very good idea to at least experiment with a proper radial field. I am fairly confident he will be very pleased and probably surprised how much better his antenna would work under those circumstances. This is especially true if he wishes to operate the antenna harmonically (eg on 80m).
    K7TRF likes this.
  7. W1BR

    W1BR Ham Member QRZ Page

  8. WB4MDX

    WB4MDX Ham Member QRZ Page

    Take a look at my MULTIBAND antenna on my QRZ page. As the earlier post mentioned, you can have multiple wires at the feed point. I use a second wire on my 160 inverted L that is 1/2 of an 80/40 trapped dipole going vertically up. It tunes well on 160/80/40 and 30 meters. You can easily make a coaxial 40 meter trap. This is a very stealth antenna for antenna challenged neighborhoods. WB4MDX
  9. 2E0LPL

    2E0LPL Ham Member QRZ Page

    Hi Jay...yes I took a look at your multiband antenna...I did consider one like that...but it would look fussy in my urban garden...I like to keep a low profile.

    I have been chatting with the guy who sells the 80m traps on ebay...he also makes a simple inverted L wire antenna c/w with 80m trap...coax fed...I may try one of those.

    The only reason I hook my antenna via the 4-1 balun is that it's internal on my ATU and connected to the end fed wire post on the ATU...so maybe I would be better by-passing the balun??
  10. WA7ARK

    WA7ARK Ham Member QRZ Page

    I would bypass it on 160m. My tuner has "jumpers" on the rear panel so that you can either use the 1:4 balun or not.

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