You have one 40ft mast, which antenna you'll install for 80/40 meters?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by 4L4AGU, Dec 6, 2010.

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  1. 4L4AGU

    4L4AGU Ham Member QRZ Page

    Imagine a situation: You have lightweight, 40ft aluminum mast, which itself can serve as radiator, or can be used to support wire antenna, or small sized vertical (maximum top loading is 10 lbs). Antenna will be placed on the roof of 9 stage building. Roof is made from reinforced concrete and sized 180x30 feet. What will be your choice for good DXing, 1/2 or 1/4 vertical, or dipole, slopper, inverted V or ?

    I've modeled all possible types of antenna, which I can fit in above mentioned restrictions (Verticals, deltas, sloppers, hb9cv, squares, zigzag, etc.). But, I'd like to hear any practical recomendations from experienced users.
     
  2. AK4BM

    AK4BM Ham Member QRZ Page

    I use something similar - I have 35-feet of fiberglass mast up at the moment. I have a full sized G5RV and a 20m dipole up (which I may turn into a fan dipole).

    It's not the greatest, but its me on the air. I want to put my 2m vertical on top, but that requires tilting the whole thing down.....maybe in the spring.

    Robert
    AK4BM
     
  3. KD0CAC

    KD0CAC Ham Member QRZ Page

    I would start with the inverted V , you may need to play with the angle by lifting or dropping the ends , some concrete has magnetic properties / iron , then the reinforcing , probably re bar .
    So having a antenna analyzer would help , or at least a meter that has forward / reflected power measurement .
    This is another one of those try it & see .
    Do not forget to bring the results back here .
     
  4. KA0GKT

    KA0GKT Ham Member QRZ Page

    I would go out and get a bottle of Mexican Coca-Cola and consume the contents, then use it as a base insulator for the mast. Then I would guy it from the top with an 8-10' diameter top hat made from the guy wires above the top guy insulators. I would feed the antenna either through a fixed antenna tuning unit or I would put an automatic antenna tuner in a weatherproof cabinet at the base. Run as many radials as possible for as long as possible across the lawn around the coke-bottle insulkator.
     
  5. KF6ABU

    KF6ABU Ham Member QRZ Page

    trapped 40m vertical/ 80m L. 40m coaxial trap at the top of the support then 25 ft or so of wire. bunch of radials.
     
  6. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    80m dipole/inverted V.

    Simple, effective and usable on higher bands with a tuner.
     
  7. M1ENI

    M1ENI Ham Member QRZ Page

    Well you could give the inverted sloper by 9M2AX in the ON4UN book a go
    mast plus loading wire from top =1/4 wave and two radial wires in line that are 1/4 wave laid on the roof they are not a ground plane they form a low impedance for the shield of the coax.
     
  8. K1DNR

    K1DNR Ham Member QRZ Page

    The question is for 40/80 meters...

    9 stages - this is how many meters high - 40 meters perhaps, 30 meters?

    It is nearly a half wave high for 80, except that I think the steel reenforced concrete is going to negate the height advantage from a radiation angle perspective, depending on how high you can go above the steel reenforced roof.

    I'd be inclined to try the vertical as mentioned with the insulated base. Perhaps 32 ground radials?

    You could go off the edge of the roof with a dipole, perhaps to another building or some type of sloper arrangement.

    If radials aren't an issue, I'd try the vertical.
     
  9. N5YPJ

    N5YPJ QRZ Moderator QRZ Page

    A fan dipole is what I would install.
     
  10. NM8B

    NM8B Ham Member QRZ Page

    easy a inverted v for 40 and one for 80 offset by 90 degrees. take a look at this link

    http://home.centurytel.net/w9wis/NVIS.html

    it will be the same thing but at 40'. at lower elevations @15' i used the elements as the guy wires. good luck enjoy some experimenting.
     
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