Time to look inside the MFJ 1788

Taking a close look at things
It's the fall and time for some antenna maintenance for me there is no tower to climb or any outdoor work for that matter. It's as simple as bringing the MFJ 1788 indoors from my balcony and having a look. I have had the cover of the antenna off in the past so it was no problem to quickly remove it and start investigating. Some of the things I look for are poor solder joints, little critters who have made my antenna home, the smooth operation of the tuning capacitor and the over all health of the components.  It was a good thing I did check the mechanical connections and without exaggerating I have to say that almost all nuts were
Checking the cap fins
loose......some very alarmingly loose! The hardware holding the stepper motor in place was the worst but not far behind was the larger nuts that held the large tuning capacitor in place. I can't remember the antenna acting funky at all but I do believe it was just a matter of time before something reared it's ugly head like a quirky SWR! Another thing I like to do while the antenna is apart and fully cycle the tuning capacitor for not only smooth operation but the equal spacing of the moving fins along side the stationary fins. There was only some minor adjustments needed to the capacitor fins.........BUT where does "Murphy"  fit into this adventure........well just as I was finishing my adjustments the antenna slipped off the TV tables I had it on and the control wire that runs the motor broke off the circuit board! Also the "feed loop" wire was distorted somewhat. The feed loop is 10
Some of the many nuts that were very loose.
Control wire torn off.
gauge wire in the antenna that is contorted into a egg shape, this little baby can really play games with how the SWR outcome on the loop is determined. I played with it when I first got the loop and that was a mistake as it occupied about 2 hours of my time to get the antenna's SWR back to "normal". I vowed to never touch that feed loop again, but thanks to Murphy it seems I have to revisit that dark cave again. I re-soldered the stepper motor wires back in place and did my best with the feed loop wire. The antenna was put back together and with my fingers cross I tested it and to my utter surprise the unit was working better than it has in the past.
Mike Weir, VE9KK, is a regular contributor to AmateurRadio.com and writes from New Brunswick, Canada. Contact him at [email protected].

6 Responses to “Time to look inside the MFJ 1788”

  • Colin GM4JPZ:

    Serendipitous posting, Mike. I’ve had the MFJ loop for about 5 years and had problems getting it to tune at all when I finally got round to tryuing it (it’s a long story, involving being in A61 for a year and not getting my licence, then coming back to GM-land with the loop in my crates). For no pareticular reason, I took it apart about 4 hours ago (!) to check for loose connections etc. as you describe, and everything seems to be all right. Don’t have time right now, but will try tomorrow to tune it, and might get back to you for some tips if it doesn’t work!

  • Alan Sarisbrick G7ELG:

    Had exactly the same problems from delivery. Also the fixing holes failed to match up to the hardware. Had to”draw ” the
    Holes to mount the loop. But it works and very well. Pity there is such a lack of quality control. No mention some assembly must be completed by purchaser Hi.

  • Mike VE3WDM:

    Good evening Colin, thanks very for taking the time to comment. Sorry to hear you are still having some issues with you antenna. Now when you say you have trouble tuning it…do you mean:
    1. Poor SWR all around?
    2. Not able to get a low SWR under say 2.0?
    3. Not just able to hear any signals on the loop?
    4. You do get a decent SWR but it changes on it’s own?
    I would be more that happy to help you to try to get the loop up and running just email me. ve3wdm at hotmail com

  • Mike VE3WDM:

    Good evening Alan, thanks for stopping by and commenting. It seems that the MFJ products do have this issue in common that the end user has to do some do it yourself repairs! It’s to bad this is the only Mag loop in the market.
    Have a good what’s left of the week.

  • Rodney, kc2lxd:

    Hi, I’m trying 2 out back together my mfj 1788 mag loop. I’m having trouble aligning the capacitance plates and nuts, where the plates will move evenly. Can you please send me a picture of it, so that I can see if there’s something I’m missing-interms of what holding the capacitance blades together with the nuts along the metal rod. Thanks!

  • Mike VE9KK:

    Good evening Rodney, I did email you (looked it up on QRZ.COM) BUT I sent you a link to this post above looks like I had a brain fart! I will check my personal photo library and see if I have a better shot.

Leave a Comment

Subscribe FREE to AmateurRadio.com's
Amateur Radio Newsletter
News, Opinion, Giveaways & More!

Join over 7,000 subscribers!
We never share your e-mail address.

Also available via RSS feed, Twitter, and Facebook.

Subscribe FREE to AmateurRadio.com's
Amateur Radio Newsletter

We never share your e-mail address.

Do you like to write?
Interesting project to share?
Helpful tips and ideas for other hams?

Submit an article and we will review it for publication on AmateurRadio.com!

Have a ham radio product or service?
Consider advertising on our site.

Are you a reporter covering ham radio?
Find ham radio experts for your story.

How to Set Up a Ham Radio Blog
Get started in less than 15 minutes!

  • Matt W1MST, Managing Editor

Sign up for our free
Amateur Radio Newsletter

Enter your e-mail address: