Portable 1/4 wave ground plane idea?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by NC0Q, Feb 24, 2021.

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  1. NC0Q

    NC0Q Ham Member QRZ Page

    My question is, would a 1/4 wave ground plane with 3 or 4 radials barely 7 feet off the ground function well? Or would I expect similar performance to a ground-mounted monopole with 3 or 4 radials resting on the ground?

    I intend to try my hand at portable QRP CW operations if/when the continent ever thaws. I’ve built this little 40 meter band radio, a “5 Watter” from kitsandparts.com, and now I’ve turned my attention to the antenna problem.

    I’m really not interested in mucking about with finding and using trees for masts, and here in Nebraska there are no summits or grueling hikes, so I am seriously considering purchasing a Spiderbeam 40 ft fiberglass mast.

    It dawned on me that a vertical 1/4 wave wire element suspended from the top of this mast would terminate about 6-7 feet from the ground, and I could simply add three or four wire radials from that point, sloping away, lengthening with mason line or something to keep the ends off the ground.

    I hadn’t really considered a portable monopole because I was thinking of a truly ground-mounted installation, with “as many radials, as long as I could get them,” and ruled it out because that sounds like a lot of wire to untangle/pack.

    My question is, would a 1/4 wave ground plane with 3 or 4 radials barely 7 feet off the ground function well? Or would I expect similar performance to a ground-mounted monopole with 3 or 4 radials resting on the ground?

    I appreciate any input.
     
  2. W9XMT

    W9XMT Ham Member QRZ Page

    The comparison below may be useful.

    It would take many times more than 4 radials for performance with its base mounted at the surface of the Earth to ~equal its performance when elevated 7 feet AGL.

    [​IMG]
     
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  3. G3YRO

    G3YRO Ham Member QRZ Page

    All the people that use quarter wave verticals on 160m will tell you that you need 40 radials on the ground to be efficient . . . but if elevated (10ft on Top Band), even 4 will work pretty well . . .

    So yes, that's a very good idea.

    Just remember that the better your radial sysyem, the LOWER your feed impedance will be . . . so you may need to correct that mismatch at the base. (for example with a shunt coil)

    Roger G3YRO
     
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  4. WZ7U

    WZ7U Ham Member QRZ Page

    Take the time to design the elevated version. Properly engineered, will take less time deploying than an equivalent quality ground mounted version, just from the ground plane wire count.
     
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  5. N4UFO

    N4UFO Ham Member QRZ Page

    Try electric fence poles every so many feet, available at most farm supply places. As even 3 feet off the ground would be way better than ON the ground. I used to have a 160/80m loaded vertical with the feedpoint about three feet off the ground with 4 above ground radials and went to 32 on ground radials and it was about the same. 'So why did I change?' you ask... so I could MOW. :D

    from this: vertical.JPG vertical closeup.JPG to this: lowband base.JPG

    Seriously, I am considering a 30m antenna with a vertical wire hung from a high tree limb down to the top of a fence and then just two radials going each way on the fence. Should work great. If I had a way to run four, would be even better.

    73 & GL!

    Kevin N4UFO
     
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  6. AK5B

    AK5B Ham Member QRZ Page

    Yes, it will be a worthwhile project---elevating verticals can actually make a sizeable improvement over the same antenna ground mounted. "Elevated verticals rock!" is practically my motto.

    Rudy Severns, N6LF did many studies with which he concluded that a monople elevated four feet above ground with at least 2 radials 9.15 to 0.40 lamda in length performed as well as the same monopole ground mounted with 120 radials. Amazing, huh?

    So your 7 foot high monopole on the Spiderpole is a very good plan. Btw, Rudy also found that while 1 or 2 elevated radials are adequate, the optimum number (if elevated) is 16, just so you know. But for portable operation 2 opposing radials is fine, and the pattern is still omnidirectional.

    I enjoy 20m portable ops with a homebrew antenna roughly half the size of your proposed 40m antenna next to the Gulf and I love chasing dx with it, FWIW. I suspect you will be please with your 40m version.

    Less ground loss and ground clutter to contend with when monopoles are elevated.;)

    Seven feet or more is also a good radial height as people won't run into the wires---just keep horses and giraffes away from them and you'll have no worries. :D

    Looking forward to seeing a picture of your set up should you go forward with your plan---I may have to do the same with one mounted on a sturdy base attached to my car's trailer hitch carrier while parked next to saltwater---thanks for the idea!

    73,

    Jeff
     
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  7. KK4OBI

    KK4OBI Ham Member QRZ Page

    Some thoughts about field deployment of your Spiderpole 40 meter vertical.

    Elevated radials need to be tuned. One radial is directional with 2-3 dB gain to that side. Two opposing radials provides circular radiation.
    A more convenient alternative to a 33-34 ft. wire radial is a alligator clip and 35 ft. tape measure or wire spool.
    For a little more cost a more easily tuned and compact alternative is a 40 meter Hamstick as a radial.
    General rule: Radials to the side (90 degrees) have 30-40 Ohm impedance. Radials angled downward have higher impedance to give a better match to 50 Ohm cable.
     
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  8. M0TTQ

    M0TTQ XML Subscriber QRZ Page

    I have worked portable with a similar arrangement (12m fibreglass pole, varying numbers of radials) and found in the end that it was less inconvenient to carry a second pole (a 10m one) and make an EFHW as an inverted-L. The performance is slightly better and it is a no-tune multiband arrangement.
     
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  9. NC0Q

    NC0Q Ham Member QRZ Page

    Thank you, everyone, for adding to the discussion, and encouraging me that the idea is sound. I especially appreciate the suggestion of tape measure radials, (not sure if I’ll actually try it, but it’s definitely a forehead slapping great idea,) the NEC comparison graph, the mention of a shunt coil for impedance matching, and the anecdotal reports of similar installations. I’m going to go this route then.

    Thanks again! Off to order the mast now.

    Edit: Forgot to say I will definitely be stopping at TSC for some electric fence posts!
     
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  10. AK5B

    AK5B Ham Member QRZ Page

    Correction for my typo in post #6 above:

    ...at least 2 radials 0.15 to 0.40 lamda... (not 9.15 to 0.40) Darned failing eyesight! :(
     
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