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Thread: antenna exp. ya'll

  1. #1

    antenna exp. ya'll

    results of prior experiment are suprising:

    i made both a 2m and a six meter dipole out of rg58 coax. something i noticed about the 234 and the 468 formula; these do get me in the general area, (and maybve these work more accurately with small diameter wire) but i need to trim off A LOT to tune into frequency.... which is a pain when things ain't at ground level.

    what i did was: i tied the coax shielding to the coax wire itselt on both parts of the dipoles, thinking more surface area for rf to run around.... more surface area, more better swr over a wider of frequency band. the entire 2m band tuned in at between 1.0 and 1.4 over the entire band.. and the six meter tuned to the bottom part of the band (50.0 to just above 53.000) between1.1 and 1.3, but shot up real fast at about 53.300)

    the next experiment will be using a three wire extension cord, tying the three ends together, to make the two dipole legs, to see what will happen. ... suspect better band width, but mush heavier wire......

  2. #2
    "Island Bartender" KG4CGC's Avatar
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    Look for some old aluminum coax. The stuff cable TV providers are taking down and replacing.
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    RIP Albi
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  3. #3
    word, bro,.... i'll also look into "big lots," hudson's and stuff like that....but if that's the case, about aluminum being more reflective, why not just use 1" PVC with aluminum foil wrapped around it, and around the foil electrical tape? it would be lighter, and a more manageable build....

  4. #4
    "Island Bartender" KG4CGC's Avatar
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    I don't think aluminum foil works that way but if you run into some of the aluminum coax described, it makes great legs. Around here, the removers and installers just leave it on the side of the road.
    I flatten the ends and melt out some of the insulator on the mounting end and drill holes to mechanically connect with bolts.
    I've enjoyed island life for 14 years. That's 10 years more than the Confederacy was around.
    RIP Albi
    When do you tell a woman you're a ham?

    It's a jungle out there. Many EQ stupidly with poor articulation.
    ~TKX

  5. #5
    ya' know ya'll. i saw a young man's video where he went so far as to make a 6m antenna out of beer cans, duct taped together end to end.... and it worked! go figure.....

  6. #6
    Administrator N8YX's Avatar
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    Look up the "double bazooka" antenna (usually employed on 160 and 80M). The use of coax cable as a radiator was to increase the bandwidth. As you approach resonance from one "tuning direction" (increase towards) the radiating element appears capacitive. Going higher in frequency makes the antenna appear inductive.

    The coax cable "radiator" offsets this a bit by lowering the Q of the antenna. That (capacitive) sword cuts both ways as you found out with your 6M experiment.

    Another antenna to look at is a coaxial J-pole. It uses a coaxial stub as a matching transformer - which is what your entire 6M antenna is essentially trying to do.
    "Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."

  7. #7
    'Grumpy old bastid' kb2vxa's Avatar
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    The beer can antenna was a novel approach to a popular broad band design, the cage dipole used since the early days of wireless. The beer can antenna WAS, not is because aluminium cans are weak and almost impossible to solder together, (aluminium solder isn't magic) but I used steel cans for everything from antennas to springs to heat sinks, but I digress. The large diameter dipole aka cage dipole was the heart of Duga 3 better known as the Russian Woodpecker, Old Timers cursed it when it perched on an ongoing QSO with that infernal 10Hz pecking. Fast forward to today, hams everywhere build and use cage dipoles because of their wide band characteristics, no need for a tuner. https://military.wikia.org/wiki/Russian_Woodpecker

    cage dipole.png
    "The universe is under no obligation to make sense to you."
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  8. #8
    Administrator N8YX's Avatar
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    One of my HF stations has a JRC JST-135 and matching long-wire auto-tuner (Raytheon AC-152E, actually a re-packaged JRC NFG-230). Another can use one of several Icom radios and an AH-2 tuner (similar to the JRC unit). When I get the stations to their next location I'm going to build a vertical cage monopole similar to the example Warren shows, but with a capacitance hat of several horizontal wires going off to surrounding support structures (trees). I'm aiming for at least 90ft height to the horizontal transition point and whatever I can get away with past that out to the ends.

    Either tuner is limited to 200w but with a decent radial field that may be sufficient for me to make contacts.
    "Everyone wants to be an AM Gangsta until it's time to start doing AM Gangsta shit."

  9. #9
    'Grumpy old bastid' kb2vxa's Avatar
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    A long time ago in a galaxy far away I had very good luck with a 6M dipole made from a plastic box at the center of 2 section telescopic tubular aluminium elements, the box held the series gamma match. Tuning was accomplished by varying the length of the elements, matching by a small air variable cap about 40pF max. The bottom of the band is where the action is so there's no need to cover it all.

    I never did like wires in trees, unless they're tall oak or mountain ash they're sway poles and when the first wind comes along SNAP goes the wire, I had one that was more solder than copper. Acrid, Ohio sounds like a candidate for a vertical I have experience with and very good luck with when I lived in West Creek, NJ and spent lots of time at K2PG working DX, the grounded vertical folded unipole. 60ft is the optimum height, it doesn't need to be a tower, a guyed mast will do nicely as long as it has 3 skirt wires held from it at about 15in with a commoning ring at the top connected to it and another a couple of feet above the ground, that is the feed point. A watertight remote ATU will load it up nicely from 160 to 40M, below 40 (remember it is wavelength, not frequency) tuning gets very narrow, it may load up on 20, then maybe not. The low vertical takeoff angle makes it ideal for DX, I had a great transatlantic 5&9 QSO on 75M phone LOL at the dipole and KW mob jumping up and down like James Brown and getting nowhere while we were using the usual 100W, they accused me of ghost talking. You know what they say about the angle of the dangle, 90% of the station is at the far end of the transmission line.

    The engineering concept is quite simple and has been used for many years in AM broadcasting because it saves expensive steel, the tower is shorter than the conventional 1/4 wave series fed tower. It was also used on pirate radio ships because it was far less likely to cause them to turn turtle and none ever did. This design puts the 90 degree (current loop) point at the top instead of the base for greater range. That's what broadcast engineers shoot for, but our multi-band operation really can't predict the outcome on harmonics without EZ NEC and an engineering degree to use it. (;->) Then you can take advantage of my experience, go out there and kick ass. You know a decent radial field helps, and I had plenty of luck with 120W PEP from a Drake TR7. For the sake of the newcomer, I was an AM Gangsta from way back and did my share of AM Gangsta shit. Then there is the VHF and a UHF version, physically different but electrically the same.

    broadcast version.jpg VHF-UHF version.jpg engineering concept.png
    "The universe is under no obligation to make sense to you."
    Neil deGrasse Tyson

    73 de Warren KB2VXA
    Station powered by atomic energy, operator powered by natural gas.

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