Metal or Fiberglass mast for field / portable NVIS?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KK4NSF, Dec 30, 2018.

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  1. KK4NSF

    KK4NSF Ham Member QRZ Page

    During the last Field Day, my group had a lot of great contacts but noticed a large doughnut of limited propagation.... from ~60miles out to ~200 miles or so. From Mobile AL, we could hit Dallas TX, or Minneapolis MN, or Washington DC with no problems but got zilch / zippo / nadda from closer locations like New Orleans, or Montgomery. Obviously, we need to improve our antenna set-up, and have decided to add an NVIS Antenna to our mix. We are leaning toward an Army AS-2259 style antenna (low sloping dipoles) for 40 & 80 meters, mainly because a few of us have practical experience using them in the field, we know they work.... and they are easy to set up.

    In our researches, we've noticed that the Army versions use metal masts with integral coaxial feed lines, while the Amateur versions mostly use fiberglass / pvc masts. A few Amateur masts are aluminum. Since we will be building our antenna, we can use whatever we want to.... but which one is better: metal, or plastic/fiberglass? or does it matter?

    Dave
    KK4NSF
     
  2. N6MST

    N6MST Ham Member QRZ Page

    Fiberglass poles are lightweight and pretty inexpensive. With a 31' Jackite pole you can support a 40 meter inverted v that's low enough to the ground to work NVIS.
     
    KK4NSF likes this.
  3. WB2UAQ

    WB2UAQ Ham Member QRZ Page

    Go with the fiber glass masts or maybe PVC. Yes. The AS-2259 uses masts (4 sections for 15 feet and a base plate) with built in coax but they were designed to have the radio immediately at the base connected by a very short piece of coax. I know this because I set up and tore down an AS-2259 a bunch of times while testing circuit changes in manpack radios. The radio must have a built-in antenna coupler because the impedance is nasty. Running 15 feet of coax down along the side of a PVC or fiber glass mast will be no different.....a transmission line running down from the 4 wire connection point to a radio directly below it with a piece of coax about 18 inches or so long. Anything else is not an AS-2259. I hope you use wire lengths that are not the same as the 2259 and are much longer:) 73, Pete
     
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  4. AI3V

    AI3V Ham Member QRZ Page

    NH7RO and KK4NSF like this.
  5. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    For a temporary NVIS wire dipole or inverted V, just about any mast will do for 20 or 30 feet. It's a matter of how hard it is to put up, take down, and stow, and cost of course. You could fool around with homemade PVC but it's weak, and other ad hoc solutions will consume a lot of time and surprising amounts of money and still not be very satisfactory IMO.

    I would seriously consider what KC8VWM suggested in another thread: 6-section 30 ft. aluminum window washing poles which are readily available at home improvement stores and are strong enough for this sort of duty. They are about $100. Make a simple stand to prevent "walking", like a board with a center hole and four tent stakes, and tie some ropes on for guys and you're done.
     
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  6. KD6RF

    KD6RF XML Subscriber QRZ Page

    As everyone above says - it makes no diff.

    FWIW, at the last mil tech demo I observed a few years ago, the folks were using fiberglass sections for their NVIS system.
     
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  7. KK4NSF

    KK4NSF Ham Member QRZ Page

    understood..... that's why we're looking at NVIS. The idea is to run the NVIS in addition to our other, higher antenna to get full coverage
     
    Last edited: Dec 30, 2018
  8. KK4NSF

    KK4NSF Ham Member QRZ Page

    you missed all the fun then! The As-2259 cannot really be appreciated until you have to set one up in the blazing desert sun, with a 20knot wind blowing sand in your face. That's living it up! ;)
    About the coupler: Since it's a one day event, I'm thinking about placing a tuner right at the base to match the impedance.
    yes indeed. I'll start with standard dipole lengths for 40&80 meters.... then trim in testing.
    We've actually looked at those.... and it's not a bad idea. I think 30ft might be too high, though. Wouldn't I get a more vertical pattern with 16 to 20 ft?
     
  9. AI3V

    AI3V Ham Member QRZ Page

    You don't understand.

    The antenna has very little to do with it.

    If the ionesphere was reflecting vertical incedent signals you would have had communications. They would have been a couple of s units weaker than 500 mile signals.

    Moving a antenna from say 60 feet to 20 feet won't make a significant difference if the ionesphere isn't cooperating.

    And changing the mast from metal to fiberglass will not make a bit of difference.

    Rege
     
    NH7RO likes this.
  10. KK4NSF

    KK4NSF Ham Member QRZ Page

    Not to be argumentative, but I understand fully about how NVIS works... and the antenna does have a lot to do with it.

    my question only relates to fiberglass vs metal mast, not the merits of NVIS.
     

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