Sunday, December 16, 2018

The MFJ loop finally has a decent SWR match!!

Homemade vertical mounting....."thing"
After doing some "playing" with the location of my 1788 mag loop on the balcony and getting really nowhere with lowering the SWR. The lowest I could get it was 1.6:1. I decided to go vertical with the loop to see what happened. Now those of you that have the MFJ 1788 loop know there is a bracket that comes with the loop for just this purpose. Well when I moved I know I put this bracket somewhere safe...........and it's still there as I can't remember where this "safe" place is!  I did try putting the loop vertical bout a month ago but at the time I was tired from all the fiddling around on the balcony and my vertical attempt was very hap-hazard. That approach did not seem to work for me either and I just left it at that. As time passed I decided to take a more serous approach at mounting the loop in a vertical position. I went to the hardware store and picked up some metal conduit and the finished product was a decent looking mount that allowed the loop to be vertical.  In a vertical position I knew the antenna would be directional but if the SWR was lower that was just fine with me. Low and behold on a certain place on the balcony the SWR is 1.4:1 which I am pleased with.The loop is still mounted inside a tripod on the balcony and you can see some holes in the tubing. When the new loop vertical bracket is placed inside the tripod tubing I slide a pin through. This stops the loop from spinning if a wind comes up. The next step will be to put some watts into it and see what
happens! It just really gets me how time just flies and all the non ham things pop up which make me very happy that in just over a  year I will be retired. I will have as much time as I need to get things done (not just ham things) I can't see myself getting board......well that is the plan anyway. Now I did mention in my last post about an update on the Sun SDRpro 2 rig that is going to have to wait for about 1 more week.

8 comments:

  1. Hello Mike, I always thought a magnetic loop should be mounted vertical. Never thought about horizontal mount. I think you hardly notice the difference between 1,4 and 1,6:1. I just ordered some cheap parts from China to make myself a remote controlled capacitor to use in mag loop projects. I've seen this on the MW1CFN blog. 73, Bas

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    1. Good morning Bas very nice to hear from you, make sure you keep us up to date via your blog on the remote controlled cap project.
      The 1.6 SWR you are correct but for me to get the lowest SWR possible means my band width is wider before I have to retune the loop.
      Have a great holiday and all the best to your family.
      Mike
      VE3WDM

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  2. Hi Mike,
    My 1786 is mounted horizontally on my small balcony. It took some playing with to find the best location. In the end I found that keeping it as far back from the balcony as possible was the answer. It is pretty close to the window. I can get 1:1.5 or better on all bands except 10m which isn't an issue these days.

    You could simplify by removing the horizontal mount and bent pipe then mount it directly to the upright with a pair of u-clamps. I use a 3 ft. piece of fence pole in an umbrella stand.

    My other tip is to open the controller box on your desktop and adjust the pot that controls the speed. I turned my down a bit which makes the fine tuning a little easier.

    Best of luck, good DX and Season's Greetings from another GTA area balcony ham.
    Paul VA3ZC

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    1. Good evening Paul, very nice to hear from another city balcony ham! The condo we were in before I had no issues with the loop SWR I could get it down to a flat match. In this place (same building) same size balcony but different shape. I have tried almost every spot and the best I can get is 1.6. In the vertical position I can get it down to 1.4 and that way I have better band width before the loop has to be retuned. Now the controller box is a great idea and I did not know you could do that.....which pot is that? I will get the print online and see if I can see it for myself.
      73,
      Mike

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    2. Evening Mike,
      Amazing how the different balcony in the same building can be so different as far as the loop goes.

      If you download the manual:
      http://www.mfjenterprises.com/Downloads/index.php?productid=MFJ-1786&filename=MFJ-1786_2A.pdf&company=mfj
      and look at the troubleshooting section at the end there is a tip about removing the cover and re-shaping the small coupling loop to get better swr and also notes about adjusting R26 to get a slower or faster fine tuning.

      Also I was wrong when I mentioned u-clamps. You can directly mount the loop to a vertical pole with the v-blocks and hardware like so:
      https://lh3.googleusercontent.com/-XzyL5jbipFk/U6xiGpQ1DoI/AAAAAAAAIZc/-20tcBNlYEw/w531-h799-no/Mag_Loop_close2.jpg

      Hope that helps a bit.
      Cheers.
      Paul VA3ZC

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    3. Good morning Paul, thanks for the idea of slowing the “slow tune” as it sure does make sense that I may be able to find the sweet spot and lower the SWR and thus greater band width before retuning.
      I have tried to retune the loop with the slow tune when the SWR hits about 2.0 but I find the loops slow tune is even to fast and the SWR just jumps up. I then use the coarse tune to go further up and then bring it down until the noise almost peaks then fine tune. Maybe when the slow tune is adjusted I can adjust the fine tune only. I don’t use the auto tune as I have found I can get a better SWR with manual tune and I have gotten very fast at it.
      One final question.....
      How slow is your blinking slow light?
      73 and thanks for the info and links.
      Mike
      VE3WDM

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  3. Hi Mike,
    I'd estimate my slow blinking light flashes 3 or 4 times per second. I can still easily overshoot lowest swr but a quick push of the fine tune in the opposite direction usually does the trick.

    I did find the reshaping of the coupling loop helped reduce swr. Mine is pill shaped instead of circular, oriented parallel to the main loop.

    Another option would be to replace the coupling loop with a longer one. The standard formula is that the coupling loop is 20% of the main loop but I found with my homebrew loops that increasing the size made it easier to tune. I think the sacrifice is efficiency but I'd give up a couple of percent in exchange for a usable swr.

    Hope that helps.
    Paul VA3ZC

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    1. Good morning Paul very nice to hear from you again, thanks for the info and I’m hoping by slowing down the fine tuning I can improve my SWR and in turn improve how often I don’t have to retune the loop as I move up or down the band.
      73
      Mike

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