I previously owned an Alex Loop which I used on several winter activations and eventually sold it. I liked the easy setup and found the performance okay. I’m thinking of once again purchasing a mag loop antenna for use in adverse weather and was wondering if there are any other commercial loop antennas available that activators would recommend? I would be especially interested in a slightly larger diameter loop since I won’t be using bands above 17M.
Consider making your own, or putting a larger diameter loop on an existing product. Use a maximum size for the highest frequency band you’ll be using, and take what you get on the lower bands. Loops performance is quite good for maximum size to 1 octave down, fair 2 for octaves down, and falls off rapidly below that. Circular loops self resonate at about 0.35 lambda circumference, so start with just a bit smaller than that for the highest frequency band you’ll be using.
Here’s another interesting variant - yes those are three loop in the antenna!
Helmut has presented papers on magnetic loop technology at Ham Radio Friedrichshafen - he seems to know his stuff and it’s good to see someone not just copying the Alex Loop (which is also a good antenna).
LNR Precision with the remote tune option. Best built loop I’ve seen yet in many ways and more durable than the others. Bought one in August and really impressed with quality overall. I’ve built several loops too and they can be fun to build. Check out LNR. They have sold them all over the world.
Loops of similar mechanical/RF construction all perform about the same. Thus with the co-ax loop variety it really boils down to how usable it is in the portable environment and what you want to pay.
In all practical use-cases the efficiency will generally be significantly less than for a full size antenna. But that may be a viable trade-off in some situations. Most of the online calculators are overly optimistic. This one seems to give realistic results. https://owenduffy.net/calc/SmallTransmittingLoopBw2Gain.htm
I don’t want to be religious about it, but I think that a Magloop is in most cases a very bulky thing for SOTA. Also keep in mind that slight detuning (by people running by, objects, the wind changing the coupling of the coupling loop,…) can kill your finals (a minimal change will turn your SWR from 1:1 to 1:8 in the blink of an eye).
Any tripod alone will weigh more than e.g. a lightweight 5 m fishing rod and this:
It is roughly about 3 dB down to a full-size dipole on 40m; no 1 - 1.2m diameter Magloop will match that IMO.
The current model still recommends the use of a T1 or other auto tuner for the fine matching (deploying the radial(s) is otherwise a bit fiddly). The next version will include an L-Match and Tayloe indicator right in the winder.
I really like Magloops for hotel operations, where I want maximum stealth and a good filter against QRM from bad LED lamps and power supplies. But on a mountain top, I think you have better options.
I’ll give a second recommendation for the LNR Precision loop. I like that it is able to cover 60, and it is about the same packed volume as the alexloop. I don’t have the remote tuner, I just sit next to it.
I wouldn’t like to carry that magnetic loop contraption up to a summit and then try to set it up in the outdoors - why suffer such punishment just to make a few SOTA contacts when a simple and efficient coax fed resonant link dipole on a fishing pole (without tuner) can be erected in less than 5 minutes and provide lots of HF contacts?
I am intrigued by the mag loops but I have been having great success with a 43 foot end-fed wire, sloping from either a tree or the tip of a 20 foot telescoping fishing pole, down to my KX1 with built-in ATU. On a recent trip in Maine (report coming later) I was able to reach a summit and drop my pack, and the total time for setup, 10 QSOs on 20m (across the width of North America and one European DX contact), teardown, and hoisting the pack again was 45 minutes! How would a mag loop compare to this? Has anyone done A/B comparisons in SOTA of mag loop vs. effective wire antenna?
Barry commented wanting a loop to use in adverse weather. That’s the reason I purchased the LNR Precision Mag Loop antenna with remote tuning. Our daughter lives in Montana and while we were there last Christmas the weather was minus 19 or so every morning and not much better as the day went on. I wanted an antenna I could use to chase SOTA on most HF bands without having to go outside and tune it somehow. This loop fit the need nicely. You could do the same on a summit using a Bothy bag for shelter or a tent if you were staying a while possibly. I also saw an Alex Loop box that contains the tuning capacitor damaged while inside of a hams suitcase. The side of the box was broken inward to the point the antenna could not be used. With the box used on the LNR antenna I seriously doubt that kind of damage would happen as is is substantially more rugged than the Alex Loop or any other loop antenna I’ve seen.