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160m mobile near ocean, radials

Discussion in 'Mobile Radio Systems' started by K3RW, Sep 20, 2018.

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  1. K3RW

    K3RW Ham Member QRZ Page

    Picked up a 160m 600w capable screwdriver a few weeks ago. Its a beast.

    Was thinking of heading to the beach in the winter during one of the 160m contests. 100w max since I don't have a mobile amp.

    Current capability for it includes a Hustler 54" extension that couples to the MFJ-1979 telescoping whip, which gets up about 17ft. It gets a bit flimsy at the top so effectively lets call in 12ft. So I have a huge loading coil, abt 17ft of whip, and I can drive on the beach.

    Would it work better to use radials into the surf, since I can get that close? Or run out 1/4 radials for 160m from the base of the screwdriver, insulating the vehicle? Something else?

    Trying to see how best to make use of the grounds I have available. But what sticks out is my element is likely to be much shorter than the radials. I suppose I could float a kite or something. Not sure if that ends up being a second problem.

    And in case I can't get to the beach, I could always head up the mountains here, so that may be a similar solution minus using saltwater radials. In all cases the truck is parked, not in motion, and I have ample space to run radials of any real length.

    Ideas?
     
  2. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Rudy Severns, N6LF, did a series of articles on radials, which have become the defacto standard. The articles get a bit complicated, but the PDF on his web site is the nitty gritty. The PDF is near the bottom of the page.

    (http://www.antennasbyn6lf.com/design_of_radial_ground_systems/)

    By the way, really large coils, say bigger than about 3.5 inches, are somewhat lossier than those between 2.5 and 3.5 inches due to distributed capacitance. And large metal end caps make things even worse.
     
  3. AA7QQ

    AA7QQ Ham Member QRZ Page

    It would be a bit cumbersome, but a 4'X50' or 100' of "Welded wire galvanized fence" (Garden fence). Either plastic coated or not. Silver solder a copper wire to it & roll it out. Couple rocks to hold it down. THat should provide enough capacitance to ground to make for some good times.
    Also, you may want to experiment with a taller lower mast (Isolated from ground-"Lower element of center loaded vertical). This will give a better efficiency.

    Ed
     
    WA9UAA likes this.
  4. WA9UAA

    WA9UAA Ham Member QRZ Page

    Just being near the ocean would be a big help. Having an efficient antenna system is the way to go, if you could put up an efficient 160M antenna you'd be golden.
    73,
    Rob
    WA9UAA
     
  5. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Being within a wavelength or so to the water will significantly improve your signal. Not necessary to dip radials into the water. You can attach radials to the base of your antenna (alligator clips) or to the car chassis.
     
  6. K3RW

    K3RW Ham Member QRZ Page

    I got a questionable bit of advice on the radials the other day. Apparently if the radials are LONGER than the main element (and unless I did a kite vertical or something, they would be), that the radials are actually a problem.

    I can see from one perspective that might be theoretically possible, but then counterpoises don't necessarily work like that. But then again, getting a EFHW counterpoise length on 160m, I see to use 5% (!), 20 (!), 100 (%) of the EFHW length, and another site said make it even longer. Huh? At 100% its a dipole, right?!

    Any insight on this one?
     
  7. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    I can't address end fed half wave miracle antennas. That is a specialized topic and depends on the individual antenna construction type, as well as feedline, and installation.

    _____________
    Radials are never a problem, especially those on the ground. You may need a matchbox/tuner, but they always improve radiation and reception.

    -Radials on the ground are not particularly sensitive to length, because they are detuned by ground coupling.
    -Elevated radials perform best when tuned to resonance (just like a dipole), but still improve performance regardless of length.

    To reiterate, anyone interested in radials should spend time reading the superb information by Rudy Severns, N6LF:
    http://www.antennasbyn6lf.com/design_of_radial_ground_systems/
     
    K3RW likes this.
  8. G3YRO

    G3YRO Ham Member QRZ Page

    That's what I would have thought . . .

    I operate 160m mobile a lot . . . but haven't found that it makes any difference !

    On one seafront near me I can park within 50 to 100ft of the sea . . . but it makes no improvemant to my radiated signal.

    Roger G3YRO
     
    Last edited: Oct 16, 2018
  9. G3YRO

    G3YRO Ham Member QRZ Page

    Also - you may find that adding radials actually makes your signal worse!

    A good friend of mine (who makes/sells antennas commercially) reckons that - certainly on 160m - it's the VEHICLE that actually radiates the signal . . . the whip just enables you to get the power out of the rig. (this is partly because a typical car only has about 250pF coupling to ground . . . so on 160m it's like you're using a balanced antenna. And the vehicle will normally be a lot bigger than the whip, so does most of the radiating.)

    Also - try using a very small loaded antenna (ie mobile whip) on 160m at home - even with a really good radial system, it's rubbish! You actually put out a much better signal with the same whip on your car.

    Roger G3YRO
     
  10. K3RW

    K3RW Ham Member QRZ Page

    I was going to use a 22 ft whip, which is a rigid 54" fiberglass whip with a 17ft telescoping whip, running 100w max. Of course, parked.

    Problem is, with that setup, the whip is 22 ft, but I could drive close enough to the ocean to throw a radial in. But with a lossy main element, but perhaps a good or even great ground this way, I seem to have defied normal antenna theory.

    Give the crazy winds at the coast I might be luck to get maybe 18ft out of 22, since the top is quite thin. A loading coil'screwdriver' thats capable to 160m takes up the rest.

    Good point on the mobile ground. Its possible I actually make matters worse by trying to improve the ground over the vehicle, or just in addition. I suppose the ultimate will be a SSB A/B test! Too bad I run digital almost always, but will definitely try it and report back.
     

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