JS1KSU's tiny mobile antennas

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KE0EYJ, Oct 14, 2017.

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  1. KE0EYJ

    KE0EYJ XML Subscriber QRZ Page

    Really impressed by the DX that Mick works with these tiny antenna's he's made for his van. He runs a 50w Icom 7300 as a mobile station, and we are often hunting longpath DX at the same time of day.

    The elements are something like 20cm high, but are large diameter aluminum tubes with a coil underneath. He has some links to more information. He works out to 6,000 miles plus on these things. I'd have to think they'd be a good HOA option for someone. He's mobile, so he can drive up to good places by the water, but I know he gets the DX, because we work similar stations.

    Thought others would like this guy's QRZ page, which has more info. He speaks/writes English, so would probably be happy to answer questions.

    sra mini_111218_0047.jpg sra mini_111218_0043.jpg
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    https://www.qrz.com/lookup#How to make the ”Super Rad Antenna” for 15m BAND
     
    N2PQW likes this.
  2. N2PQW

    N2PQW Ham Member QRZ Page

    Derek,
    Thanks for sharing this! It's interesting how little vertical height of each antenna constitutes the radiating element. I'm sure the metal rack and/or roof of the van are critical to the performance, but that's just my instinct talking.

    I operate HF almost exclusively while mobile these days, and I can understand his enthusiasm.

    I imagine that van is perceived as a behemoth in the cities of Japan!

    Cheers,
    David / N2PQW
     
  3. K4SAV

    K4SAV Ham Member QRZ Page

    I see pictures of the tuner, but there isn't a very clear picture of the antenna, which is apparently those horizontal bars on top of the van.

    Your link doesn't work.

    You can find more information about this antenna, and similar ones, with a Google search. It's amazing how many people don't understand how antennas like this work, and then proceed to invent new laws of physics to explain their operation.

    Jerry, K4SAV
     
    NH7RO likes this.
  4. KE0EYJ

    KE0EYJ XML Subscriber QRZ Page

    I saw another person who said that this was a sort of magnetic loop... not sure about that, but it's all new to me. I'd just like to hear of people finding something small for an HOA setting that might work for them.
     
  5. KE0EYJ

    KE0EYJ XML Subscriber QRZ Page

    Betting you saw it, but...

    Search JS1KSU on QRZ and scroll down his page most of the way, for more info. He gives sizing and build info. in English.

    It's really odd... the link did work before. I clicked on it a few times, earlier today. Must have been something germane to my browser or cookies.
     
  6. KI7LGN

    KI7LGN Premium Subscriber QRZ Page

    Well, Jerry, you'll have to explain to me, because I don't understand how a 12" tall HF antenna that is mostly coil can work at all, nevermind work well.

    73,

    Matt
     
  7. K4SAV

    K4SAV Ham Member QRZ Page

    Matt, it's good to see that you are using some logic. If the people that invent these very small antennas would do the same, they might have a desire to investigate how they work.

    There are several very small antennas that people have invented. They all work because of common mode currents. The feedline or something else connected to the feedline becomes the real antenna. The little part on the top (usually claimed to be the antenna) is actually acting as a tuner to maximize the common mode currents.

    I can't see if the horizontal bars on top of that van are connected to the coax shield or not, but my guess is that they are.

    A good recipe for the generation of common mode currents is a small antenna that has a very low real part of impedance (very low radiation resistance) and very high reactance, and no choke on the feedline. That's the reason my XM-240 (two element 40 meter Yagi) has a low SWR on 160 meters. The balun for that antenna doesn't work very well on 160 and the common mode currents on the feedline couple to the tower and the tower becomes the real antenna (not the 40 meter elements).

    Jerry, K4SAV
     
    Last edited: Oct 14, 2017
    NH7RO likes this.
  8. K8JD

    K8JD Ham Member QRZ Page

    Skeptic's View
    Usually the size of the antenna in respect to a wavelength is directly proportional to the strength of the radiated signals .
    When the propagation on the bands is good and the callsign is exotic enough the small antennas do work enough to be heard.
    I would guess the stations he works with the tiny antennas are very well equipt with tall towers, huge Yagis and the best receivers.
     
  9. AF7ON

    AF7ON Ham Member QRZ Page

    This is an insanely small antenna, but the coax is connected to the antenna coil and the shield to "ground". What is "ground" - the vehicle body, roof rack, or something else?

    I should note that in my long-ago ZS6 days I was in a regular sked with a fellow South African ham in Johannesburg on 10 meters to another friend in the USA. On one occasion, I was receiving my local friend (about ten miles away) very well, but our contact in Ohio reported that he could barely hear my colleague. It turned out he had tuned the finals of his tube amplifier with his pi network without connecting the output to his antenna. Sometimes propagation will do amazing things for you, even without an antenna!

    Mike
     
    NH7RO likes this.
  10. K8JD

    K8JD Ham Member QRZ Page

    Antenna-less QSOs
    I accidently worked a friend a mile away on 10M with a "cantenna". I was testing a speech compressor I just built and the dummy load leaked just enough RF to get out a mile. My friend heard me and gave a 5/7 report :D.
    True story !:eek:
     

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