End Fire Wires close to each other, any problems with this?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N1AOA, Jun 14, 2021.

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  1. N1AOA

    N1AOA XML Subscriber QRZ Page

    Hello, I have a 120ft end fed going one direction in the yard in a sloper configuration. Planning on putting another one about 90 degrees to this, also sloping.

    I will never use both antennas at the same time, so I don't see a problem. They shouldn't touch, but might be close, say a foot or less apart.

    No problems with this? Let's say they do touch, but only operating one at a time? big deal?

    thanks for any advice

    Paul
     
  2. W4HWD

    W4HWD Premium Subscriber QRZ Page

    You will have induced voltage on the unused antenna. How much? Depends. At right angles and low power it will be low, at higher power or anything near parallel it will be higher. I have three wire antennas within 100' of one another and parallel (it's the only way I could hang them); I use a mechanical antenna switch to keep the induced voltages out of my auto tuner. Seems to work.
     
    N1AOA likes this.
  3. WB2UAQ

    WB2UAQ Ham Member QRZ Page

    Hi Paul,
    Do you have a Nanovna? If so see how much coupling there is between the two antennas measuring S21. I have 26 to 28 dB of isolation between two antennas in my yard. There will be interaction / radiation pattern distortion but by how much......would need to run 4NEC2 or other program to determine by how much. I suspect that it would be difficult to be sure even running a modeling program because there are many variables such as where the transmission line is situated and how it is terminated etc. I have not learned enough about 4NEC2 quite yet to do it myself. I am not sure if is possible to model the effects of the transmission line on a "parasitic" antenna:) Would be interesting to hear if others have actually done this.
    73
     
    N1AOA likes this.
  4. N1AOA

    N1AOA XML Subscriber QRZ Page

    unfortunately I do not have a Nanovna
     
  5. N1AOA

    N1AOA XML Subscriber QRZ Page

    I will use a mechanical switch between the two (alpha delta switch). So, induced voltage will affect transmit and receive?
     
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    What is an "end-fire" wire?

    Have you ever looked at the pattern of an EF~HW wire? It is virtually identical to a center-fed dipole of the same length. There is no directivity along the wire... Putting one end of a dipole near the dirt (sloper style) only compromises it. Much better to keep both ends of dipoles (regardless of how they are fed) as high as possible.
     
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  7. W4HWD

    W4HWD Premium Subscriber QRZ Page

    Induced voltage will affect neither because it's inducing the unused antenna. If you use a good antenna switch (like the alpha-delta) with good port isolation you'll keep that voltage out of your rig and tuner. Elecraft said my KAT500 could handle the induced voltage, but I didn't want it milling around in my tuner ; if they're wrong a $100 mechanical switch is good insurance against having to replace a $700 tuner.

    On the air, there may be some pattern skewing but I really don't care, can't do anything about it if it does, seems to work and all that.

    Most of us have to compromise to get on the air and having all these wires close together is a compromise.
     
    Last edited: Jun 14, 2021
  8. WA7ARK

    WA7ARK Ham Member QRZ Page

    What Paul did not describe is how he plans to switch from one antenna to the other, how he feeds the wires, how is the antenna grounded or not?

    Much different situation if there are two coax runs that stay in place with a coax switch at the shack end compared to running a single coax with a remote switch/relay that connects the single coax to one antenna or the other...

    In order to know what to suggest, I would have to know more details... Coax length?
    feed method?
    ground under the antenna?
    details of the coax switch (unused coax open/shorted)?

    It all effects the coupling between the antennas.
     
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  9. N1AOA

    N1AOA XML Subscriber QRZ Page

    ok, that's what I needed to know, thanks!
     
  10. N1AOA

    N1AOA XML Subscriber QRZ Page

    One transformer grounded at the feedpoint (bottom of sloper); one transformer won't be grounded (up high on the roof); each has it's own RG-8X run of about 80 feet. Both coax's enter shack through a grounded entry panel. Coax switch inside the shack. The unused ports on the Alpha Delta 4B switch are grounded when not in use, and grounded when in use.
     

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