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. 2E0LPL

    2E0LPL Ham Member QRZ Page

    Ok guys...I have a 160m top band modified inverted L end fed wire antenna...its 38mts long or around 120ft.

    It works against copper ground stakes and works well on top band and 80m...had contacts across the Atlantic from the UK a good 3500mls on both bands.

    I have been using it on 80m also...its a bit twitchy to tune with my MFJ tuner on 80 especially down at the CW end of 80m.

    A month ago one of the finals blew in my rig after I was using 80m...it was suggested me using 80m on my 160m antenna end fed may have been the cause... it's a quarter wave and resonant at 1800khz...even though I had a reasonable tune on the ATU.
     
  2. WB5WPA

    WB5WPA Ham Member QRZ Page

    What did your tuner say? Did it go high SWR?

    I lost driver transistors once on account the rig had aged and the hardware had loosened up.

    I always tune for 1.5:1 or better SWR. No loss of PA transistors yet.
     
  3. 2E0LPL

    2E0LPL Ham Member QRZ Page

    Just a bit maybe 1.7-1 possibly 2.0-1 nothing dramatic.
     
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Something in the tuner may have arched momentarily, and that could create an instantaneous near-short circuit for the PA.

    It's very tricky to use an end-fed 1/2-wave antenna which is what you have there on 80m without using a suitable matching transformer (unun) on 80 (switched out on 160) to bring the native impedance down to something lower than several thousand Ohms.
     
  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    And how tweaky was the tuning? IOW, if you run a manual tuner did the tuning solution result in one or both variable caps being opened all the way up with very little meshing of the plates? That's a typical difficult tuning solution and one that can easily lead to arcing in the tuner. If it's an auto tuner it's harder to know but you can get a pretty good idea of how tough the match is by how long the tuner takes to find a decent tuning solution if it runs a long time and basically gives up at a mediocre or poor match then you probably shouldn't transmit high power into that load.

    The slam dunk solution is to add an 80m trap about 15 to 20 meters from the feed point. You could fine tune the antenna (you'd want to trim some of the 160m wire at the end after adding the 80m trap) but as long as you bring the SWR down a bit you could still run your tuner to clean things up. Getting the antenna to resonate on both 80m and 160m is ideal from a coax loss standpoint and could let you switch the tuner out of circuit with this antenna but realistically coax losses on 160m and 80m usually aren't too high unless your coax runs are very long or you're using thin, high loss coax so shack tuning to clean up SWR can typically work.
     
  6. 2E0LPL

    2E0LPL Ham Member QRZ Page

    Ok I should have said at the first post...the manual MFJ941e tuner has a built-in 4-1 balun.

    The wire antenna feeds directly to the ATUs wire post and then through the 4-1 balun...no coax feed.

    I think both caps both part open.

    A trap sounds like it may be an idea?

    Thanks guys for your advice so far.
     
  7. WB5WPA

    WB5WPA Ham Member QRZ Page

    Here is a parallel tuned network (L and C) that matches the ends (or an end) of a 1/2 wavelength wire (dipole?) on 80 meters. The red wire is the *primary*, and notice how loosely it is coupled to the white-wire secondary on the small plastic peanut butter jar. The red wire is adjusted for 1:1 SWR. It takes very loose coupling on account of the high Q of this tuned network.

    Again, this network is for matching H-Z antenna "ends", 3k to 5k Ohms Z roughly to 50 Ohms. It will probably outdo anything you can wind on a ferrite core. This is what the "old school" engineers and hams would use in the early years 'cause ferrite donuts weren't invented yet!

    BTW, this is called "Link coupling".

    IMG_3414.JPG

    Here is a finger in there for size comparison:

    IMG_3416_FingerComparison.JPG


    Side View:


    IMG_3430.JPG
     
    Last edited: May 25, 2019
    AI3V likes this.
  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    A 4:1 balun is "nothing" for trying to feed an end-fed half-wave, whose native impedance is thousands of Ohms.

    Takes more like a 49:1 unun, which actually isn't difficult to build (7:1 turns ratio).
     
    N7BDY likes this.
  9. WA8OLN

    WA8OLN Ham Member QRZ Page

    If you have room for the 160, just add another 1/4 wave wire for 80 coming off the same feed point. Done it since November and it works great. Simple works for me.
     
    WA9UAA likes this.
  10. WA7F

    WA7F Premium Subscriber QRZ Page

    I’ve run a few remote tuned end fed Inv-Ls and 130’ of insulated copper clad steel wire has always tuned well for me on 80 and 160 meters. Try adding about 10 feet if your Inv-L uses insulated wire or about 15 feet if it’s bare copper. Some radials might help as well.
     

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