Temporary Mag-Loop Antenna in the Back Yard, and the Mounting Location for my Vertical (Part 2 of 3)
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- เผยแพร่เมื่อ 12 ม.ค. 2025
- Here is the only HF antenna I have up right now (really missing my Hex Beam!), an MFJ-1788 Magloop. Using the inside controller box I showed previously, you move the plates of a tuning capacitor with a motor that's controlled by voltages sent up the coax. It tunes from 40 through 15 meters, giving a very high Q antenna in a super-small package, compared to a 64-foot long 40 meter dipole anyway.
Recently, I moved this loop to a new location in the attic above my garage, and it has been doing decently well there. I would hate to have it as my only antenna unless conditions (like a HOA) forced me to.
I also explain how I'm going to feed and mount my Butternut HF6V vertical antenna. Still getting ready to do that several months later, but it's spring now, and time to get it up in the air. Maybe I'll shoot another video or at least some stills of getting it installed.
If you are interested in the MFJ-1788 and want to see what the controller box looks like, you can see a close-up of it in my ham shack here:
• First Look at My New H...
NOTE: I've copy/pasted this more-complete personal evaluation on the MFJ-1788 below. It was originally a response to some questions in the comments on my Xiegu G90 video, but it thought it might also be better located here:
I actually have two MFJ-1788 antennas. The older one took a tumble off of the top of a shipping container to the pavement in a sudden breeze, and I've never fully restored it to 100% yet. I had it on a temporary tripod without guys. It was a quickie Field Day setup. My bad. I guess I liked the design enough to buy another--call me crazy I guess.
The newer one that is sold by MFJ now has a few minor improvements over that older model, such as white LED backlights on the meter, and higher voltage to the tuning motor. The antenna and controller box you see in my videos is the newer one, and I have no serious complaints about it.
I'm actually a bit of a mag loop fanatic. I hand-built the first one I ever owned, and it's still my favorite. When band conditions were a little better in about 2008-10, the first two contacts I made were to Hawaii and Maryland on 17 meters within about 10 minutes of each other, using my 15-watt Elecraft K2 on SSB. It was supported by a piece of 1x2 wood pushed into the grass in my front yard. It looked like a copper lollipop! The bottom of the loop was only about 2 feet above the grass.
I was amazed at that performance! So that motivated me to play around more with these interesting antennas. I still have it, and I keep telling myself that I'll add a remote tuning motor to it one of these days, but it's pretty low on my priority list right now.
So back to the 1788: It works as advertised, and it doesn't take long to get used to the clever tuning method with the remote box. It works well enough, but you can also just push the UP/DOWN Fine Tune buttons and listen (or watch, if you have a band scope or panadapter) for a peak in the background noise. You'll be almost always at the peak noise and lowest SWR at that point.
I pre-wired my house with a number of runs of LMR-400 coax when we built it last year, so I moved the MFJ antenna to a room over the garage, which is where it is now. I have a lot of electronics in the house, and it picks up more hash and digital birdies than I would like, but that's not the antenna's fault.
I can easily make QSO's with Japan and the south Pacific with it, but I almost always use my G5RV antenna that I set up in my back yard in July 2021. I've yet to find a signal where the MFJ loop was stronger than the G5RV, but it's not bad considering that it's so small and totally stealth.
By the way, my G5RV antenna is also an MFJ antenna. It works very well, but you need the space for it. I have it set up like an inverted V with the center at about 25 feet, and the 51-foot dipole legs sloping down to about 6-10 feet. Using an antenna tuner, I can work 80-6 meters with it. It comes ready to roll out and put up in the air, and it's pretty well-made, so kudos to MFJ for this inexpensive yet very decent design.
Another thing I really like about the MFJ loop is that it will take 100 watts with no complaints, so you can use it with just about any ham transceiver without worries of capacitor flash-over.
As a mag loop fan, I must also admit that I have a Chameleon F-Loop and an Alex loop Walk Ham portable loop. The Alex loop is a clever design, very compact, and awesome as a grab-and-go portable QRP antenna. I think I bought it at Gigaparts a couple of years ago. His website is: www.alexloop.com/
I have not had a chance to use the Chameleon loop yet, but it's on my "fun" list of things to try.
The big advantages over the others that the MFJ loop has is remote tunability and high power handling. That really makes it a no-brainer to put up in an attic and forget about it. As far as directionality goes, I honestly don't see enough that I would want to add a rotator to it. This is based on my subjective use, and with the antenna mounted vertically, as shown in this video. I believe that MFJ has recommendations about when to mount in vertically or horizontally. I have tried both on 10-20 foot masts outside, and I think the efficiency is higher when it is mounted vertically, especially when you are closer to the ground. Horizontal mounting is better when you can put it up higher, and it's really the only choice if you want to keep rainwater out of it.
Caveats: Any mag loop loves to couple a lot of its energy into nearby metals and wires, which causes its efficiency to plummet, so keep it as far away from your house wiring, metal ducts, and rain gutters as you can. As you can see in this video, mine is way too close to my gutters.
Another thing to know is that the MFJ mag loop efficiency goes down as you go lower in frequency because of the longer wavelengths versus the small loop circumference and pipe diameter. I recall that it's something like 17% efficiency compared to a full-size dipole on 40 meters. Again, this is just physics, and is not unique to the MFJ design alone. Some homebrew mag loops actually use 2 or 3 turns of the aluminum or copper pipe (or coax) to raise efficiency on 40 and 80. Like a mobile antenna, you might be able to tune those bands, but as the ratio of the antenna size to the wavelength gets bigger, and efficiency falls.
My two last criticisms of this antenna are the somewhat flimsy black plastic weather covering, and the price. If you mount this antenna vertically outside, you WILL get rainwater in it unless you come up with some extra sealing around the top and sides, which MFJ warns against doing.
The housing has weep holes in anticipation of this, but I don't think it's sufficient. Mounting the antenna horizontally will keep it much drier inside.
As to the price, MFJ has put a very beefy tuning capacitor of their own design into this antenna, and I really like the aluminum tube that is its most distinctive physical feature you can immediately notice. Along with the remote tuning box, and the clever tuning method you quickly learn, I can see these items used in the antenna somewhat justify its cost. I just wish it was $100-150 lower. If it was in high-volume production, I'm sure they could lower the price substantially, but virtually any ham gear by definition is not going to be high-volume numbers compared to, say, an iPhone. That's just how the economics of manufacturing are. Trust me, I've been in the high-volume consumer electronics business my whole adult life.
I hope you find this info helpful.
73,
Dave--K7DAA
Hello from Lehi. nice set up looking forward to see the progress!
Thanks--me too! Wish I had some progress to report. I'm sort of waiting for the spring thaw now. Nice to hear from a nearby neighbor! Are you a UVARC member?
@@DaveAndrus Hey Dave got my XIegu yesterday. now time to set up the antenna. Noji from the Club will be helping me with that!
@@vaq130 Noji is a great resource! I definitely want to hear from you when you get it hooked up to your new antenna. I haven't been on the 146.76 repeater much for the last year, since I don't commute now, but if you happen to hear me there, I'd love it if you called me back and we could chat about it over the air!
@@DaveAndrus will do I got a new vanity so if you hear K7OMD that is me.
Hi Dave!
Hi Mike! Awesome chatting with you about non-business things. Thinking of getting a ham license some time?
So would you recommend the antenna?
Well, I think I would have to say that I might suggest trying anything else first. That doesn't sound like much of a recommendation, does it? 😉
Depending on your available real estate, even a random-length long wire > 40 feet with a tuner might work better. This is not a terribly efficient antenna on 40 meters, although 20-15 meters are OK. The efficiency is really compromised if you mount it near metal, like my rain gutter that you can see in the video. This antenna as it sits right now is pretty deaf. I need to move it out into the yard with >20 feet of open air around it, but I can't because of the dog's fondness for coax.
If you can put out a wire as I mentioned, or a dipole, even if not terribly high in the air, or a ground-mounted vertical, you might be happier. You can buy a lot of other antennas for the cost of this one, so you have to weigh the relative value. If you are in a situation where you really can't put much of an antenna outside, then this MFJ antenna might be your last resort. I hear that some people have it in their attic or inside an apartment and are happy with the result. I've never tried that, but maybe it might work.
With half the cost of this loop antenna, you could buy something like a Hustler 6BTV vertical, push a 4-foot pipe into the ground, mount the antenna on it, and throw out a few random-length radials on the ground (even if they can only go in 1 or 2 directions away from the antenna), and you would be miles ahead. You would also have a small slice of 75-80 meters, which may or may not be useful to you.
Speaking of attics, if you are thus constrained, if you have about 14 feet length available in your attic, I would suggest the MFJ-1775 mini-dipole that works on 40-2 meters, or the Cushcraft D4 if you've got about 36 feet. If you do this with either antenna, try to avoid mounting it such that AC wiring runs parallel to it for much of its length. Due to the fact that these antennas look more or less like a horizontal pipe, you might also find other mounting ideas that could work if you need stealth. Let me know if I can help more, I've been an antenna experimenter all my life, and have several antenna patents as well.
I run my MFJ-1786 on 11 meter sideband lower 38 running it with a Icom 7300 and I have absolutely no problem shooting DX all over the country. Great antenna for noisy areas and it does null out electrical noise. Had mine for 6 years and love it 😍
@@gburlin Actually, I'm really glad to hear that. Sounds like a nice setup!
I bought one. It was garbage construction. I sent it back.
Yeah, that's always been the problem with MFJ. Sometimes you get a well-built unit, and other times it looks like they don't have any outgoing quality inspection.