By Conrad Trautmann (N2YCH)
I tried using an Alpha Antenna 100w 10-40m mag-loop antenna for a POTA activation. I operated on FT8 so I could monitor where my signal was being received by using the PSKreporter.info real-time signal reports from stations that spotted my transmission. I really didn’t know what to expect or how a loop antenna would perform in the park compared to a vertical or wire antenna. Did it work? You bet. Would I recommend it? I’ll share my observations and results below and let you know at the end.
I bought this antenna used on QRZ.com’s swapmeet. It was clear to me upon receiving it that the prior owner had taken very good care of the antenna. I set it up on my patio for a quick test before heading to a park.
It sets up quickly. The tuning is a little challenging to learn at first but there’s no doubt when you get it right, since the received signal is easy to peak once you find resonance. The tuning knob has three turns from 40m up to 10m. Moving it slowly from the bottom of the HF band up to the top, you’ll find the sweet spot and you can peak the received signal on your radio’s S-meter. I checked it with my RigExpert antenna analyzer and as you’d expect, the bandwidth was very narrow, but it was resonant and the SWR was 1.4:1.
The Alpha mag loop can do 100 watts SSB but only 5 watts on digital modes. I fired up my KX3, set it for 5 watts and called CQ. I made three quick contacts and was satisfied that the antenna was working. I checked the spots on pskreporter,info and found it interesting to see a narrow band of stations from Minnesota and Wisconsin down to Florida spotting me.
On to the park: Indian Well, US-1684 in Shelton, Connecticut
Knowing that the antenna was working, I brought it out to one of my favorite places to activate, Indian Well State Park (US-1684). Again, set up was fast and I was able to tune up on 20 meters pretty easily.
The antenna was receiving the FT8 signals at S-9 with the KX3’s pre-amp off and you can see below that I was decoding nearly 50 stations per FT8 cycle. If you look closely at the JTAlert screenshot below, you can see I was receiving stations from all over the US as well as Canada, South America and Europe. There’s no doubt the mag-loop can hear very well.
I called CQ and had a few responses right away. However, I was finding it challenging to get stations to reply. It took almost an hour for me to get my 10 contacts to activate the park, which is unusual. I should mention that the space weather was acceptable, sitting just below Kp3, so that wasn’t the reason.
Once again, I checked Pskreporter.info. Interestingly, it had the same pattern of spots that I saw when testing the antenna at home, a band from Minnesota to Georgia. Of the first 10 contacts I made, four were in North Carolina, two in Florida and the rest were coming from within that narrow band who could hear me.
I understand that a mag loop is directional, so I tried moving it 90 degrees to see if it made a difference. Not really. The spot map looked the same after the change in direction. I was able to receive a few more EU stations after I moved it. I did have to re-tune the antenna after I turned it, the SWR had gone through the roof.
For comparison, after struggling to make contacts on the loop, I decided to set up my “go-to” antenna of a 17’ telescoping whip on a 10’ mast with a counterpoise.
I unplugged the mag loop and plugged in the vertical using the same transceiver set at 5 watts. Take a look at the stations who could spot me on PSKreporter now…
Clearly, that same 5 watts from the KX3 had better coverage on the vertical than using the mag loop.
Here’s a screenshot of WSJT-X on the vertical (click image to enlarge):
Once I switched to the vertical, I knocked out 10 more contacts in just 20 minutes.
So, after all that, what do I think?
The Mag Loop sets up quickly, uses very little space and finding resonance isn’t difficult to do. It receives very well, of course this is one of the true advantages of mag loops, is their inherent ability to receive well in noisy environments.
As an antenna to use for transmission? Well, I think this is where the challenge lies, for me anyway. It was certainly hearing stations way down in the noise from far away. However, as you can see by my real-time reception reports, it did not give me the wide transmission coverage that I’m used to with the vertical. Maybe this would be different on SSB with 100 watts, but it’s a difficult to measure SSB reception like you can with digital.
Can you activate a park with it? Yes, indeed. Would it be my first choice for POTA? Probably not. If you were using this on SSB, the antenna itself (not the radio) would need to be re-tuned for every frequency change (if you were hunting), which is not convenient. If you are the activator, then you could tune up for the frequency you selected and it would be good to go.
My next test with this antenna is to try tuning it to a WSPR frequency and comparing spots it receives to my other antennas. I suspect this it where it will shine.
Stay tuned!
Another excellent article, Conrad!
I personally believe that having a loop in the antenna arsenal is ideal. There are situations (as you said, when QRM is present) where it can be beneficial.
Otherwise, it’s hard to beat a wire antenna or good vertical, especially if you plan to hop around the band a bit.
Thanks for the report! We look forward to any updates!
Cheers,
Thomas
Hi Thomas,
based on my field test, I tend to agree…vertical or wire antennas seem to perform better. I can usually work who I can hear and the loop was the first time I ran into a situation where that wasn’t the case . Also, a friend pointed out that I didn’t have a lot of height on the loop…getting it up in the air might make a difference.
I plan to test its receive capability on WSPR against a 30m dipole I have at my QTH to see how it receives in comparison. I’ll report back.
73
Magloops are a compromise but they work , it’s just a quarter wave vertical is better
On 40m the magloops are very inefficient but they do work
Most magloops are able to manage under 25w of power handling which works well on cw but can be a problem with SSB but they do work
Magloops offer advantages over regular antennas and are useful for certain scenarios
I love the Chameleon, AlexLoop and the MFJ-935 (uses wire loops instead of coax)
Happy antenna fun
The Chameleon used to be a kit but it’s easy to make and works great
Great report! I’ve become a fan of the idea of using PSK-Reporter for real -time comparisons. Good to see an antenna comparison with it, I’m running my own RF power output comparisons with portable setups this year using PSK-Reporter.
“It took almost an hour for me to get my 10 contacts to activate the park”.
Yes, Thomas, this is exactly my experience when using the original Alexloop for activating a park in FT8. Sometimes it takes even longer, which can be frustrating. For FT8 I am using the IC-705 connected to SDRcontrol running on an older iPad.
On the other hand, during good conditions I am “working the world” in FT8 using the Alexloop indoors in my home and 10 watts power out of the IC-705. Mostly on the higher bands, but from my location in Germany I even have a 40 m FT4 contact with AA3B in my log. With the Alexloop standing indoors.
Originally, I bought the Alexloop for cw contacts with SOTA stations when operating with my IC-703 from my home QTH. Too high electric noise on the vertical on the balcony on 40 m, but the magnetic loop worked (/received) fine for this.
FT8 is a very slow mode. I am sure you will get better / faster results when trying in cw with the magnetic loop.
Sorry, Conrad N2YCH, just noted that it´s your report. Many thanks for this.
Regards, Harald DL1AX
Copy that, no worries. Thanks for the comments Harald.
73, Conrad
Very interesting report, thanks!
I agree that a loop antenna is great to have in the toolbox. I’ve had amazing results with my AlexLoop (5W SSB contacts across the country in the hotel room at night), but I’ve also had miserable failures… The failures have made me a better operator though I think
My very first POTA attempt was on a business trip. This was before my CW days and I was attempting to do a 5W SSB activation using the AlexLoop and IC-705 in the Lost Dutchman State Park in AZ. I think I made 2 contacts the entire time (while sweating like crazy the entire time).
My next work trip to AZ, I went back to that park to conquer it. Used the 705 again but brought a mast (no trees in AZ) to support an EFHW. Also had CW in my toolbox. Great activation!
I am surprised that turning the loop caused a change in SWR. That seems to me that you might have a loose connection somewhere, which is not good for efficiency.
FWIW, my AlexLoop is my most used antenna for POTA. Contrary to your experiences I find my AlexLoop performs as well any portable vertical I have used on 20m and up. It is noticeably a compromise antenna on 40m but does very well on the other bands. I always cringe when a see a portable magloop with manual tuning that is rated at 100 watts. I really hope that people realize that sitting within arms reach of a magloop is not safe if you are running 100 watts. Even at 5 watts I always try to sit in the broadside null. One other hint. The efficiency of a magloop is directly proportional to the enclosed area, which if you recall from your Geometry lessons is maximized by having a perfect circle. Yes this is one situation where neatness counts. Taking an extra minute to make the loop into a tidy circle will improve its performance, if only slightly.
72 de VE3WMB
Hi Michael,
I was also surprised that the SWR changed…but a tiny tweak was all it needed to bring it back in. I think the connections were fine, and I was able to dial it in for 1:1 SWR again.
Thanks for the tip on the geometry…and for your comments.
73, Conrad
Efficiency relative to the band your choosing with a 1 meter loop will be down on 40 for xmit. Now if that loop was a 7 foot loop or one that is a double loop with 4 inch separation you might have much better results. Efficiency in better the higher in freq you go with highest freq your loop will do… 10 or 15 meters relative to the 40 meter capability with a mag loop formula out there that will show you efficiency versus size. Higher the freq the more directive results. Vertically orientation with no ground effect is nice. I am in process of adding another 150 pf to my 10-30 meter MFJ 150 watt max loop, 3- 50pf 10kv caps in parallel, and it shows receive on 40 working great. I just need to add a switch for the extra capacitance when doing 40 so that I can utilize 10 meters when I want to. Another 40 meter antenna that takes 1KW, that I enjoy is the 40 meter Isotron which gets out well and is very small.
Thanks Rich. I was operating on 20m this time. I may try 10m and see how the signal reports look.
73, Conrad
Antenna aside, with only QRP levels of power using FT8, you are the little guy on the block. I am using 3-4 watts and in order to complete QSOs I often have to be “frequency agile”. That is to say, very often (in fact most often), I will find a clear FT8 slot in the spectrum, get a response to a call or CQ only to see that my signal is then swamped by a signal that is using exceptionally more power (up to 20db sometimes). Understandably with such a low output as mine I probably am not even a dot on the waterfall display. At that point I move the transmit curser to a an apparently clear slot and transmit again hopefully to get my message out. Even then I could be stepping on another QRP station that is not visible on the waterfall. So far it has worked well, but there are times during the day when with QRP levels of power, whether using a vertical, EF wire antenna, dipole, magloop or whatever, you’re going to be sorely challenged. That’s part of the challenge of QRP. Once I move out of our home (I’m closing in on 79 years), my salvation will in fact probably be a magloop. DX is great but not an essential element of my amateur radio pursuits. This was a great report. I enjoyed reading it. Thanks and hello to all from Winnipeg, Manitoba, Canada. EN19iv.
Postscript to the above comment:
72 es 73 de Jim Williams VE4BWG
Nice try with the Mag Loop Conrad. They are very directional
so you might turn it 45 degrees from where you were to get across the US from CT.
Nice article !
72,
W1FMR in NH.
One thing I’ve learned from my loops, as with all antennae but specifically loops is metal is not your friend. I can get a 1:1 but if I place it on the porch within arms reach of the metal patio furniture it’s not greater than 1.4:1, so your tripod might be hampering you.