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hf antennas

Discussion in 'General Ham Radio Discussion' started by rfoverlord, Mar 18, 2007.

  1. rfoverlord

    rfoverlord guardian of freedom

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    :( come on doc you started it now finish it. I'm just leary of anything mechanical as far as antennas go. If it burns up or get stuck what do you have????


     

  2. 231

    231 Member

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    Yes it does...or rather, certainly did compared to wire beams I've built. ;)

    I'd be curious to know how many you guys have made and tested with tubing over wire to where you are so confident? :shock:

    [​IMG]

    This pic was taken during heavy winds (50+ mph)...so it's not 100% straight. It's direct fed and I probably should have used a 1:1 balun but at the time it didn't seem to need it. But it's not 100% done yet either...just my prototype. I'll probably put a balun on when I get my primary support system in. I'll be adding an additional director element at the same time, too.

    Build one yourself and see. I don't care if you don't believe me as it's just what I'm seeing. My meters show things consistently and I get good reports (especially on 10 & 11 meters)...but I guess the people I'm talking too are in the clouds. :roll:

    Yea my F/B & F/S ratios go out some, but it works well otherwise. In fact, even with that minor inconvenience it's still one of the best beams I've run (for what it is). The tests I ran prior to putting it up (for further testing) were a full 2 S-units over a center fed coaxial dipole 20' higher than the beam. F/B on center band is about 40db...consistently. ;)
     
  3. W5LZ

    W5LZ Crotchety Old Bastard

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    rfoverlord,
    If it get's stuck, just un-stick it. Not exactly that simple, but not really all that hard either. As for burning it up? Well, which part? The motor can be replaced at almost any hardware store or Wal-Marts. Look for the cordless screw drivers. One that runs on 9 volts or so is better than one that runs on 3 volts. Or your local hobby shop ough'a have a few 12 volt motors that are about the right size.
    If you're talking about burning up the coil part of the antenna... tsk, tsk, you ought'a know better'n that - LOL.
    What did I miss?
    - 'Doc
     
  4. Hamin' X

    Hamin' X Active Member

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    I will admit that I have not built two identical Moxons, one with wire and one with tubing. Also, I have not tested them against each other, since I do not have an antenna test range to get any kind of meaningful results.

    I use MultiNEC and either the EZNEC, or NEC-4 engines to do my antenna modeling. These modelers allow for wire, or tubing of various sizes. Using the MultiNEC Excel template, I am able to change the frequencies, or any other dimension, or combination of variables, including height above ground. MultiNEC then calculates a spreadsheet for everything and allows me to see Az/El charts and graphs of Frequency, SWR, Reactance, Resistance, Angle, F/B, Gain, etc. These can be viewed individually, or in any combination, on one, or multiple graphs. The Az/El pattern charts are the typical ones that you see. It also generates Smith charts.

    When I find time, I'll post some charts of what a multi-band Moxon might look like.

    Rich
     
  5. 231

    231 Member

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    Very cool HaminX. ;)
    I'd love to see it...and will give you my real life results vs. your software. But in the mean time, I really didn't want or mean to hijack this thread...and don't want it to go that direction. So we can start another thread down the road later. ;)
     
  6. C W Morse

    C W Morse Active Member

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    Several hints. Stay away from PVC loading coils. And the screwdrivers that move up and down aren't really THAT bad. Depends on the builder's machining. The trick is mating the loading coil and the mast tubing IF the coil is machined correctly it will move up and down as needed and remain "still" no matter WHERE it is in the antenna's travel. PVC just isn't stable mechananically or electrically. It WILL burn up pretty quick if you put too much RF on it. It doesn't depend on the finger stock to hold it in place. Stay with Nylon, or Phenolic coils. Most of the screwdrivers are pretty reliable mechanically. And they won't just "fall apart", either. Just do your research and choose carefully.


    73

    CWM
     
  7. rfoverlord

    rfoverlord guardian of freedom

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    well i'm pretty sure it will be a Hi-Q but maybe a high sierra? it depends how much i want to fuss with mounting/matching. and i haven't seen to many current reviews of the Hi-Qs lately. There are a few on e-ham and some of the individuals doing the reviews, I actually value their opinions based on their backrounds.
     
  8. W5LZ

    W5LZ Crotchety Old Bastard

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    CWM,
    Tell me about PVC being heat sensitive! :) But you can turn that to your advantage too (pun intended), if you don't happen to have a lathe. Position the loading coil on the PVC coil form. Apply slightly too much power and have the wire melt it's way into the coil form. Then, re-tighten the @#$ wire. Do that too long and you end up with 'curly-fries' like at 'Arby's! If done at highway speeds, you get a 'L' shaped loading coil (don't ask! I'll lie! I'd never do such a thing). :)
    - 'Doc
     
  9. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    That's so you can run an inverted L on 75m mobile. :LOL:
     
  10. C W Morse

    C W Morse Active Member

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    Sure, but it would be really tough to control the amount and evenness of the heat. I use black nylon with pre-fabbed grooves. I have developed a way to spin the wire on in minutes. Then I fully attach it at both ends. Then wait. It WILL expand and become loose. I tighten it and lock it down. Let it sit. Tighten it again in the grooves. Let it sit again. Tighten it again. Sit again. It will then settle in on the coil form and remain in place. When it is done, it make for an antenna that will handle up to 1500 watts SSB and also remain stable. I like the nylon pretty well! You can melt anything if you try, but the nylon holds up very well! :D
    I have, indeed, seen PVC coils that made claims for 500 watts. They became expensive slinky toys! :p


    73

    CWM
     
  11. Happy_Hamer

    Happy_Hamer Administrator
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    What vehicle are you going to put the antenna on?

    I had the High Sierra Pro 1800 and the High Sierra Sidekick.

    My buddy uses the Tarheel II and I seen it and really like how "clean" the antenna looks compared to the High Sierra.

    So I bought the Tarheel II and even had it custom painted :D

    Works just as well but looks better

    [​IMG]
     
  12. rfoverlord

    rfoverlord guardian of freedom

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    my burban is getting it after i go through the bonding process and ripping out the old gear, so all i need is an antenna to get that out of the way. I told the xyl that i had to many projects, as i just bought a universal towers 9-50 and a couple of the gulfalpha dual polarity 8 ele. (vhf/uhf) and i was going to get a mosely tri bander but now i'm leaning towards a tennadyne 8LP. the new tower is only going up 40' so i can gain a little more in wind load.
     
  13. rfoverlord

    rfoverlord guardian of freedom

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    HH how has that new Tarheel been working out? I'm still undecided on what i want. I do know i want to run a Turbo Tuner with it, any experience with them?

    73
     
  14. dxhound

    dxhound Active Member

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    Ive been looking at the ATAS 120a because of its vhf and uhf capabilities. I know those who have had the ATAS 100 and loved it.
     
  15. rfoverlord

    rfoverlord guardian of freedom

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    :? You might want to go with a seperate ant. for vhf/uhf and the yaesu doesn't do 75/80mtrs. I'm sure you have looked at the reviews.
    http://www.eham.net/reviews/detail/5984
     

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