Spring tuneup on the MFJ 1788 Loop antenna

Oliver was going to watch over the operation
Each year around this time I bring the MFJ 1788 Mag loop in to take the covers off and have a look around to see how it has faired over the past year. This antenna has been great for me with my very restricted condo situation. I have been able to get all around the world on CW with most of the time 5 watts QRP. I am about 60 feet in the air, it's on the balcony and we do have other condo's all around us but having said that I have been very pleased with the performance of the loop. At first tuning the
Cleaned covers

loop took some time but now I really have the hang of things and am able to tune it in no time. Most of the time the SWR is flat or very close to flat on all bands it's designed for. Now as for band width on 15m it's very nice but as you move closer to 40m it gets very narrow but it is what it is. When reading the reviews of this antenna on Eham many have mentioned how the antenna when new from MFJ had an issue or two. My antenna also out of the box had an issue with the tuning box with a switch that had to be replaced. I purchased the antenna through DX engineering and they were very fast to have MFJ send me a replacement switch.
Now back to my yearly maintenance, the antenna is covered with a patio table cover to help it look like balcony furniture and funny thing is it does not affect the SWR at all so the cover is kept on all the time. This year I picked up a new cover as the old one was 4 years old no longer water proof and showing it's age. I removed the plastic covers  and cleaned the inside out which were really not all that dirty. I found as I do each year some loose nuts and bolts that require
Keep track of parts 
snugging up but this year I noticed one of the nut/bolt combination seemed to have some burning on it. This was one of two nut/ bolts that help secure the loop to the tuning cap. All other nut/bolt combinations were fine it was just this one that I ended up replacing with close substitution from my nut/bolt collection.  I have posted a picture of the nut/bolt that was removed, any suggestions as to what may had happened? The nut/bolt was not at all loose and it was only this nut/bolt that had an issue. One other thing I like to do is run the tuning cap full turn in both directions looking for smooth operation, spacing moving fins against the stationary fins and the function of the micro switches that stop the tuning cap at the end of each end.  Overall the antenna was in great shape and just to make sure once it was all back together and covered with new cover I tuned it through each band to make double sure all was well.
New cover and ready to go
Nut/bolt that was replaced
New nut/bolt installed

Checking fin alignment 

Mike Weir, VE9KK, is a regular contributor to AmateurRadio.com and writes from New Brunswick, Canada. Contact him at [email protected].

8 Responses to “Spring tuneup on the MFJ 1788 Loop antenna”

  • Harry K7ZOV:

    Mike, You are making me feel bad. I have a MFJ-1886, 10-30 mhz loop. I have had it for 12 yrs now. Bought it used. Had the motor go out about 4 yrs ago. Opened it up for the fist time I have had it. Changed the motor, replaced both micro switches. cleaned and tighten it all down and out it back in service at 20 ft horizontal. Ran it for another 3 yrs. Took it down and put it on a home made tripod at 4 ft and use it for my outside shop antenna. Have not opened it ever again. Rain, hail, show, sleet and lots of sun and still working great. This is one tough antenna… I guess it is one tough antenna once you get past the lack of MFJ quality control. It seems they don’t have one. Or he/she/they are related to Martin F Jue and can’t be fired… Have fun with yours. One day I might try to pick up the like yours or add vac cap and get it to sing on 40 meters.

    73 Harry K7ZOV

  • Mike VE3WDM:

    Good morning Harry, it’s true these antennas seem to go and go once you get past the overall “MFJ experience” Now when you had to order parts for the antenna did you do it through MFJ or source out the parts? The reason I’m asking is because I have read and heard that getting parts from MFJ can be challenging and other times they just don’t seem to ever come.
    All was well with the antenna at this end except for the what looked to be RF burned nut and bolt that was replaced other than that is was just a fast look around at it.
    Have a great week Harry and as always very nice to hear from you.

  • Ray, w5xe:

    Thanks for your interesting report Mike. I too have a 1788 but have it
    ‘mounted on a 5 ft chain link fence. It is vertically polarized and seems
    to work as well as my DXCC multiband dipole at 35 ft. Only problem I have
    is getting it to tune near the top end of 40 meters. Still it is less than
    2:1 and overall very pleased. I purchased the antenna in case I ran into
    antenna restrictions or had to move into an apartment. So far not. Anyway
    it is a good antenna and does work well in a restricted situation.
    Ray, W5XE

  • Dick N3HKN:

    40 meter query: You mentioned the tuning width. How much of the band does it cover? And another, has it been exposed to freezing weather and did the temperature effect the motor rotation? I built a 100w 20m loop and the frozen motor gave it one season of life. A horizontal mounting seems the best in terms of WX and bugs nesting. The cover is clever and insures a long life.

  • Mike VE3WDM:

    Good afternoon Ray and thanks for taking the time to comment, with my loop (MFJ 1788) in the CW section of the band and for me that’s in around 7.000 to 7.040 I can get anywhere from flat to the high end of 1.8:1. Having said that I have found the loop works like a wet noodle on 40m so I have never really used it for that band at all. I have even tried during world wide CW contests when there are very eager ears at the other end and I just can’t really get state side with out multiple repeats but then again I am only operating at 5 watts.

  • Mike VE3WDM:

    Hello Dick very nice to hear from you, as I mentioned to Ray in the earlier response I really don’t use 40m as I just can’t seem to make contacts with it. This loop has been exposed to very cold weather (up to -25C) and the motor has not had one issue in the cold weather. Mine as you can tell is horizontal as well and yes I have had now and then bugs finding the loop to be a good home. This is one reason I take the loop apart once a year to have a look around. The cover I have on the loop is also there to not expose the fact that I have an antenna on our balcony as the condo my not take kindly to that.

  • Harry K7ZOV:

    Hi Mike. Dealing with MFJ for parts is a nightmare. It took about 4 calls and being redirected, before I found someone who could get me to the right motor. I did find the original mfg. and discovered that they made the same exact motor (size and shape) with different voltages and gear ratios. but in the end I got mine from MFJ. The newer units appear to have a slightly different form factor and gear ratio then mine. I suspect mine is well over 15 yrs old and maybe older. However it works and works well from 10-10 meters and that is all that counts.

    The micro switches I had in my junk box. Not a big deal. Since you have a newer unit them mine I would not worry about having a issue getting a replacement if you need it…. unless you do it 15 yrs from now…

    73 and have a great week. Harry

  • Mike VE3WDM:

    Thanks for the info Harry .
    Until again 73,

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