Sunday, March 31, 2013

THE STORY OF AN ANTENNA


     I have mentioned my fit-to-the-space G5RV antenna, but never tried to show the whole thing.  So I shall:
     Here's the entire antenna in a kind of Cubist perspective, from the 2x4 post at the back fence, to the swing tree, to the next pole, up over the roof, to the feedpoint and "X" that carries the balanced feedline over the roof peak to the TV antenna pole on the chimney and, finally, past the front roof peak to the tall tree in the front yard. 

     It's a huge image -- click to see it more closely, if you'd like.
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11 comments:

  1. Turk TuronMarch 31, 2013 at 9:59 PM

    Thanks!

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  2. drjimMarch 31, 2013 at 10:38 PM

    As we used to say back in Northern Illinois, if your antenna stayed up through the winter....IT WAS TOO SMALL!

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  3. Roberta XApril 1, 2013 at 6:22 AM

    This one broke very early, which was when I confirmed I couldn't reach the eyebolts Jim "Tree Machine" had installed when he took care of the part of the front yard tree that fell a couple of years ago. I set a new eyebolt as high as I could manage but the antenna sagged over the winter and was in contact with the roof peak until I restrung it Sunday by shortening up the suspension rope and insulator at the TV antenna pole.

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  4. Dave HApril 1, 2013 at 12:14 PM

    NASA's been doing mosaics like that with photos from their probes and rovers for years. I like the effect created by keeping the wire aligned while the frame is tilted at all the different angles.

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  5. drjimApril 1, 2013 at 3:37 PM

    What are you using for wire? The CooperWeld stuff doesn't stretch, but man, what a PITA to work with!

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  6. Roberta XApril 3, 2013 at 6:26 AM

    Just #12 house wire, I think. It's actually a commercial antenna -- a full-size G5RV, in which each half and the associated side of the feedline is made from a single piece of wire. It's insulated; this makes very little difference in antenna performance.

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  7. drjimApril 3, 2013 at 12:51 PM

    OK, just curious.

    I'm using #10 from Home Depot for the elevated radials on my Shakespeare AT-1011/SGC-230, and it's held up pretty well for the three years it's been up. The only annoying thing is the clear plastic "skin" on it tends to degrade from UV, and starts to peel off. Makes the radials look like they're shedding their skin!

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  8. Dave HApril 3, 2013 at 8:04 PM

    I worked with several guys at a radio shop in Columbus who used electric fence wire for their wire antennas. It's light, tolerates weather well, is solderable, and it's CHEAP. At the time you could get a 1000 foot roll for about $20. It's galvanized steel wire so it will rust through eventually, but most of those guys were changing their antennas every few years anyway.

    You should have seen the continuously-loaded 75M vertical I built when I was in high school. It was a 12 foot piece of bamboo stuffed in the end of a 10 foot piece of 2" PVC pipe, stabilized with wooden wedges and glued with RTV. I wound 120 feet of #12 stranded copper in red insulation all along the length. It looked like a fly rod with a gland condition. Mounted it vertically on Mom's chimney with a few random (and too short) radials. During the Blizzard of '78 the wind blew so hard it flexed until it touched the roof, then the ice froze it in place. Over the next few weeks bits of it would melt free and it would pop up a little higher above the roof. I replaced it in the spring with a center-loaded dipole.

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  9. Roberta XApril 5, 2013 at 7:41 AM

    Ahhh, snakewire! I think my G5RV uses wire without the clear-slick outer, which is really only there for improved abrasion resistance and to make it easier to pull through conduit. So it might be MTW (machine tool wire) as opposed to THHN ("house wire").

    Love your antenna story, Dave -- what kind of BW did the continuously-loaded whip have? (And was it a continuously-loaded hemi-torus when it froze in an arc? :)

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  10. Dave HApril 5, 2013 at 11:25 AM

    Thanks. 3:1 SWR bandwidth was about 12 kHz as I recall. (Not that the radio cared. It was a Drake TR-3 - as long as it didn't arc everybody was happy.) I built it for a single frequency because I was in MARS at the time and needed to make the statewide SSB nets. I was a Tech at the time and didn't have any other reason to be on 75M.

    I didn't have the guts to load it up once it was tacked in place by the ice. I was afraid of setting fire to the roof.

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  11. drjimApril 5, 2013 at 3:23 PM

    Yeah, they had the "regular" wire there, but you had to have a Home Depot person spool it off and cut it to the length you wanted, and they were nowhere to be found.

    So, I just grabbed a 500' spool and got out of there as I wanted to get the radials finished so I could use the antenna!

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