6 Meter/50mhz Magnetic Loop For FT-8 And More

Discussion in 'Amateur Radio News' started by KJ4YZI, Dec 8, 2017.

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  1. AK5B

    AK5B Ham Member QRZ Page

    Kudos to Bob, VE3UK for coming up with such a brilliant STL design and implementation. I can already envision one atop my car and another out on my back deck. Maybe a third mounted horizontally ( 1 wavelength or more) out in the woods behind me (assuming the tuning doesn't shift much in shade). Having two feed methods for the 18" work of art is cool, too.

    But shame on Eric for shamelessly promoting the latest digital fad and failing to mention 50.125 and the phone frequencies/modes as if they don't even exist---believe it or not, there are still a few of us diehards that love 6M phone (and/or cw) and couldn't care less about the digital mode of the week.

    I still monitor 50.110, 50.125 as well as check for cw beacons below there when I can. 52.525 FM simplex can be fun in the summer Es season, too. F2 propagation may be gone for a few more years but Es, tropo, TEP and meteor scatter will continue to periodically thrive during these otherwise lean years.

    Another omission or slight error was describing December as totally dead---a small but reliable spike in sporadic E occurrences happens around this time of year, too.

    It would have been nice to actually seen the loop hooked up to a six meter rig and hear the noise peak as he tuned the cap plates. Dead band? No problem and no excuse---we six meter nuts are used to listening to the frying pan for hours at a time and tuning by ear for the noise peak is a good way to tune a STL (out in the field or without a swr meter).

    Earlier this year I attempted to build my own 6M STL* with copper HVAC tubing and large copper plates. After seeing the 6M-F video I now realize I probably made my cap plates too large---so I'll have to cut them down and try again---it didn't quite tune the way I expected it would and I put the whole project on the back burner. Now I'll have to get going on that again as this inspired me.

    Despite a few things I would have liked to be included I still very much enjoyed Eric's latest video, seeing a neat Magic Band antenna and learning about VE3UK's latest product (keep up the good work, Bob!).

    73,

    Jeff


    *(please, let's drop the "mag loop" moniker; folks, it's really a misnomer at best)
     
    KA0HCP and KK5JY like this.
  2. KK5JY

    KK5JY Ham Member QRZ Page

    ;)

    Despite the more severe effects of skin effect, a 6m STL can be very effective. I have only worked CW stations with mine, but it seemed to have just as much success as other participants. It would probably work even better if I flipped it horizontally, but I never got around to trying that. 6m doesn't open often enough to hold my interest. :oops: If HF conditions continue to deteriorate, 6m might become a better band than 20m. :eek:

    It would be an interesting comparison, though, to see how copper compares against a similar surface area of aluminum for 6m operation. The OP's antenna seems to have a generous surface area around the main ring.

    I would really like to see a version of the OP's antenna that had a motor drive on it. That would drastically increase its utility, since it seems to have a substantial amount of Q, even outdoors.

    You're probably right -- it does lead to confusion. The ARRL got it right in their Antenna Book (at least the most recent one) -- they use the titular term "Small Transmitting Loops" for that section of the book.
     
    AK5B likes this.
  3. KQ0J

    KQ0J XML Subscriber QRZ Page

    Why would you screw around with a goofy ' mag loop ' for 6 meters when a REAL loop is a reasonable size? I have thousands of 6M contacts and over 350 Grid squares on a homebrew 6 M loop made of water pipe.
     
    VK6APZ, MW1CFN, KQ6XA and 1 other person like this.
  4. W4MAL

    W4MAL XML Subscriber QRZ Page

    Because that is what they do. It's does get old. 73
     
    K5XS and K7LZR like this.
  5. KD6IL

    KD6IL XML Subscriber QRZ Page

    They respond better to M fields when receiving. Like most loops. "High Q Loop?"

    "Studio-Transmitter Link" is a pretty established acronym to steal. "Dave Loop" works for me.
     
  6. MW1CFN

    MW1CFN Ham Member QRZ Page

    Loops are great antennas and can work as well or better than wire antennas if their environment is good.

    It's nice to see good engineering. But do note that a loop can be pretty ugly and much more roughly made without affecting performance. Also, the primary (small) loop is very popular, but almost always improved upon using 'pseudo-gamma' matching.

    Somehow, commercial loop makers end up charging $1000 or more for their products. A homebrew version can be built in minutes, for maybe $200 if you had to buy a NOS vac cap, and just a few $ if not.
     
    AK5B likes this.
  7. KQ6XA

    KQ6XA Ham Member QRZ Page

    1.
    I wondered the same thing about such a loop for 50 MHz.
    A quad loop is about 4 and a half feet on a side.
    The diameter of a circular "quad loop" is about 6 feet.
    The circumference is about 20 feet.

    So, the 18 inch diameter shortened loop with capacitance loading for 50 MHz can provide a reasonably efficient antenna that would sit on a desk top.

    2.
    "STL" has always been Studio Transmitter Link to most radio techs and engineers who have a background in RF or Broadcast.
    But, it seems that "STL" has taken on a new ham radio lingo meaning as Small Transmitting Loop.

    It might even be possible for both types of STL to exist along side each other :)

    3.
    However, we should point out that the video makes the all-too-familiar (but absurd) snake-oil claim that goes something like this:
    'I made hundreds of contacts on my antenna while other operators couldn't make a contact with a dipole or beam'.


    The reality is, that a shortened loop has to be really well designed and built, yet still struggles to be almost as efficient as a dipole.

    [​IMG]
     
    Last edited: Dec 10, 2017
    W5PFG likes this.
  8. VE3UK

    VE3UK Ham Member QRZ Page

    That could be an issue, however the instantaneous bandwidth of about 200KHz provide a good margin for drift either side of your fixed frequency. This antenna was designed more as a teaching aid, and for portable/indoor use. Not recommended for permanent installations without further refinement. 73 Bob
     
    KK5JY likes this.
  9. VE3UK

    VE3UK Ham Member QRZ Page

    The initial reason for such a magnetic loop was to have a "teaching/learning" aid where interested home brewers could assemble and learn the basics of a magnetic loop antenna that will work. Then hopefully apply that knowledge to building one for HF. Many hams enjoy learning using visual show-me techniques. Even something as simple as the gamma match is illustrated and can be useful to those who are not as familiar with various mechanical techniques. Trust me, as someone who has been designing and building magnetic loops for many many years, I struggled with the idea of making one for six meters for the very reason you state. None the less it is a nice project for educational purposes, and it does a respectable job in tight or portable locations. Thank you and 73.
     
    KK5JY likes this.
  10. KK5JY

    KK5JY Ham Member QRZ Page

    Thanks for chiming in. :) The loop designs on your profile page look very well executed. Do you do your own aluminum metalwork and welding?
     

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