Doing the MFJ loop happy dance!!

For some time now I have been trouble shooting my MFJ 1788 loop off and on. I have had a problem with getting 20m to tune. The best I could do was an SWR in and around 12 to 1 and really that is not good at all. Even with that SWR the K3 tuner was able to drop it too a flat match but odd things were still happening....for example
1. Tuning the loop for max noise (as low SWR was not happening) did happen but as soon as the rig was tuned in any way the noise dropped to nil.
2. Once max noise was achieved and I transmitted the max noise was gone again.
3. There was no spots on the Reverse Beacon Network while giving the tuned match a go.
4. When transmitting power levels were all over the place from 1 watt to 5 watts.

I had posted my 20m tuning problem on 2 loop user groups and had some great advice but nothing seemed to even come close to solving the problem. I then emailed MFJ  who very promptly emailed me back and advised me to change the shape of a 12 gauge copper loop that was located inside the loop. Easier said than done this involved removing half the plastic cover on the loop and changing the shape of this loop then
Adjusting the loop
checking the SWR. The hard part was trying to figure out where the sweet spot for 20m was on the loop  was. The loop would read an SWR of 12 to 1 no matter what adjustment I gave the loop. I ended up tuning the loop for the highest noise level I could hear. I figured this was as close as I could get to the sweet spot for 20m. Adjusting this small loop did not really change anything and I was getting frustrated! The best thing I find when this happens is to put the project aside and do some thinking. I did just that over the past few weeks I enjoyed the bands the loop would tune and thought about my next move. The loop consists of a rotating capacitor that tunes the loop via a motor. I had been reading on the loop reflector sites and a reoccurring conversation was how quality control at MFJ was very low. For some reason I wanted to check the spacing of the capacitor plates on the loop antenna . It turned out the plates had a warp to them and at the low end spacing was good but in and around
Some plates to close
20m's  some of the plates were very close and maybe touching each other. After some time of tweaking the plate spacing I was able to have equal spacing for the full rotation of the capacitor. The SWR on 20m is now down to 1.4 to 1 and that was the problem as I put the loop back together I kept an eye on the SWR to see if it changed at all. The piece of  equipment that really helped me out with this process was the MFJ 259B analyzer. This unit made tracking my SWR very easy, bottom line is the antenna is now working great and now it's time to get on the air and see how 20m is preforming from the condo.
Mike Weir, VE9KK, is a regular contributor to and writes from New Brunswick, Canada. Contact him at [email protected].

8 Responses to “Doing the MFJ loop happy dance!!”

  • Richard Daily, KB5FLA:

    I might be hard to tune also if someone was shooting me to turn me on and off 😉

  • Mike VE3WDM:

    Good evening Richard……..ok then.

  • Dave W8EIR:

    Great news Mike, I have been following your process with the antenna. I am debating in whether to get one or not.

  • Harry K7ZOV:

    Glad to hear you found your problem. I have been having a ball doing digital with my horizontal mounted 1786 on 20 meters. I find MFJ to be beyond excuses when it comes to problems like you have. They make tons of equipment every year of many, many designs. When they work, they work quite well. If not they would have gone out of business decades ago. What I still can not figure out is how pin headed management is when it comes to quality control. They have been hammered on it for decades with no visible improvement. Instead of making QA a top priority, they rather just shrug their shoulder and offer a no questions as fix or replace limited warranty. To me that is both really dumb and sad. But I know that if I buy new or used MFJ products that at least 25% of the time I might have to open it and fix cold solder joints or missing ones. Once that is done the unit will perform as advertised for a long time.

    My comments for the day…hope I catch you on 20 meters

    73 Harry K7ZOV

  • Mike VE3WDM:

    Good evening Dave, great to hear you have been following the antenna progress. If you are thinking about getting one there are some issues as you know but if you either get past them or win the lottery and get an antenna without any issue that would be great. I will be posting some more items about the antenna in the near future as well.
    Thanks for taking the time to stop by and comment.

  • Mike VE3WDM:

    Good evening Harry and nice hearing from you again, yes I agree with the QC at MFJ and them just not wanting to fix it. They would make so much more if the product was improved to preform as advertised. I have sent them some emails and they were promptly answered but really for an antenna worth 500.00 Canadian these things should just not happen at all. With all my other MFJ products I have not had a single problem but this antenna was another issue but I hope I have them all ironed out now.
    Thanks for the emails Harry and hope to see you in the waterfall.

  • Richard Daily, KB5FLA:


    Had to poke a little fun at the mistype. Of course my typing is always perfect 😉 I could only wish. Self taught typist from a Greg typing book as a teen many years ago. On a manual typewriter. Long story.
    Great article. Keep up the good work as I really enjoy the blog. Thanks for all the effort that goes into producing it.


  • Mike VE3WDM:

    Good morning Richard, Ah yes a mistake that I have made all to often myself thanks for the support and taking the time to re-comment.
    Have a great week.

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