Magnetic Loop Question

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W8NSI, Nov 22, 2016.

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  1. W8NSI

    W8NSI Ham Member QRZ Page

    I am using copper tubing. The coil of #6 will be silver soldered to it. I am looking at 20-10 meters for the freq range. I do like that idea of usina LARGE toroid placed around the loop and coupling coil to the coax wound onto it. I will have to order one to size for experimenting.

    I just joined the Magloop Yahoo Group and expect that I may be able to find answers there.
  2. AK5B

    AK5B Ham Member QRZ Page

    Good deal of info and inspiration on the MagLoop Group, for sure. That and Rich's site is where I got my first inspiration to build a STL.
    Do check out VK4AMZ's site as well as this excellent 32ppg treatise on the subject by the acknowledged loop guru VK5KLT linked here:

    Just curious; what size tubing are you using and do you know about the KI6GD loop calculator? It's a godsend, IMO.

    Also, please explain why on earth are you soldering #6 wire to your element (if I am reading your post correctly; I have had a glass or two of wine thus far...:D)

    73, Jeff
    W8NSI likes this.
  3. WA4SIX

    WA4SIX Ham Member QRZ Page

    Seems that he has a ferrite rod already & wanted to use that for a coupling transformer. I think he has been steered from that idea.
    Go through the Yahoo group over the past year or two & most questions will be answered.

  4. W8NSI

    W8NSI Ham Member QRZ Page

    I keep seeing references to this magic loop calculator but I guess everyone assumes that everyone else already knows about it so its web address isn't mentioned. I looked up KI6GD on here and he has NOTHING on his bio page about anything.
    Why on earth am I soldering the wire coil to the copper tubing??? Well it is darned aweful hard to wrap 1 inch diameter copper tubing around a ferrite rod. So I am using #6 wire to do the coupling to the copper loop. This is NOT intended as a QRO loop antenna BTW.
  5. WA4SIX

    WA4SIX Ham Member QRZ Page

  6. AK5B

    AK5B Ham Member QRZ Page

    Sounds like you've got things all wrong! You're actually trying to wrap 1" tubing around a ferrite rod? Or that you are soldering a 6ga. wire to the element as well?

    Better take a break and read up, do your homework before proceeding further. Leigh's article is a great place to start. So is the photos section of the MagLoop Group; that might give you some immediate insight, too. AA5TB has a lot of loop info and let me re-mention VK4AMZ who also has a site with several well-written pages with photos and analysis of his large 160/80/40M loop that he constructed atop his garage (and has had great success with, I might add).

    I don't mean to discourage you but somehow you got off on the wrong foot already. Take a step back and look at what others have done.

    There is no easy way to link the KI6GD calculator otherwise I would have done so. If you search "KI6GD loop calculator" (all three words) his website should turn up where you can then download a zip file or something like that. Once installed and/or opened it will be a handy item on your desktop forever more.

    Good luck!

    PS: Just noticed Ed linked an Italian site where the calculator is currently hanging out---thanks, Ed!
    WA4SIX likes this.
  7. AF7ON

    AF7ON Ham Member QRZ Page

    Yes indeed! From his original sketch, the OP seems to indicate inserting a small coil in series with the main tubing antenna element right next to the tuning capacitor. I assume that this is the ferrite-coupled feed.

    There are two problems with this. First, the capacitor is a high-voltage point and it will be a challenge to feed close to this - exactly why most designs use a coupling means at the low-voltage point opposite the capacitor. Second, the inserted coil will add significantly to resistive losses of the loop, dramatically reducing its efficiency. The large-diameter main tubing element should be connected directly to the capacitor using large-area low-resistance contacts. The only feasible way of providing a ferrite-coupled drive is to use a toroid large enough to pass through the main tubing element - and locate it away from the capacitor.

    Finally, if your soil isn't very good, you have to mount your loop at least a tenth of a wavelength above ground to reduce earth losses.

    But don't let us put you off - do a few experiments yourself to get the feel for how these antennas work - you may come up with something new and different.

  8. AF7ON

    AF7ON Ham Member QRZ Page

    I should have said a toroid large enough for the tubing element to pass through it! But you get my meaning!
  9. MM6IXH

    MM6IXH Ham Member QRZ Page

    Aye Jeff you are correct I am 250 yards from the salt water and reception is very good here Russia clear with strong signals even Egypt /India.
    America is not so strong as Canada but western signals are often swamped with central europe on high power . I look on qrz at some of the worldwide stations with huge beams 100ft high and wonder if they need any propagation to talk on HF. Just bought a 3453 admarality vernier tuning knob on Ebay today looks like a good piece of kit for tuning a loop with reference scale for returning to frequency . Only hope I am clever enough to get through the ham test soon ,,fear of morse code kept me from doing it years ago.

    Cheers Robbie
  10. AK5B

    AK5B Ham Member QRZ Page

    Very good, Robbie; The salt water is good to have close by; it is like liquid copper if you know what I mean. The vernier tuning dial is something else to certainly come in handy as loops tune so narrowly that you can zip right past the sweet spot if you're not careful; anything with a reduction drive like that will aid manual tuning a lot.

    When building a loop I make sure my Faraday coupling loop is the correct length by seeing how well it tunes manually before setting up the remote tuning motor and such; if I didn't have a low RPM DC motor to use the loop could still be tuned manually but it complicates things considerably if the rig and antenna are farther than a few feet. One trick to use in that situation is to turn the volume up on your rig and listen for the sudden noise peak outside---or use a baby monitor system so you can hear what's going on at your operating position while you are way out in your garden fiddling with the coupling loop or tuning shaft.

    Know what you mean about the big guns on HF; seems like they can work the world at will sometimes---although that will be less so now that we are on the downside of the sunspot cycle.

    One distinct advantage to using a small transmitting loop that is often overlooked by many: STLs radiate RF as well as receive RF at all angles in a half-donut pattern from the very horizon to straight overhead (and all points in between). A big Yagi on a 50 or 100 foot tower might well radiate/receive at a low angle for DX but at a slightly different angle above or below that there will or may be a deep null in its pattern where the DX will not be worked or heard; therein lies the beauty of the small transmitting loop which has no such nulls to begin with!

    I have worked some terrific DX with my little loop a few feet above the ground in my back yard and I suspect that their inherent "half-donut" radiation pattern often accounts for these delightful achievements.

    To the OP ( and I must apologize for straying a bit off-topic here); Please try a conventional feed method at first and experiment later for best results. These loops can be tricky to build and operate unless you really have a good handle on things beforehand. I didn't start with much technical knowledge which is why I scoured the internet for every source of information about small loops for months before I actually went ahead and built my first STL. I looked at a lot of photos to see how others had done and it helped me a great deal. There are a few hams whose callsigns I can't quite remember now who also have some very good sites regarding their STL builds---I will endeavor to track them down soon and post them here for further enlightenment---they really helped me, at least.

    73, Jeff

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