Yesterday, I posted the photo above on Twitter.
I couldn’t help it: I’m not an “Instagram Moment” kind of guy, but the fall leaf colors this year have simply been stellar. Any excuse.
Where was I? Oh yes…
Truth is, I was in the front yard practicing my loop tuning skills by hunting parks across 30, 20, and 17 meters.
The loop is the excellent Chameleon F-Loop 2.0 (which has since been replaced by Chameleon with the 3.0 version).
I’ve used this loop a few times in the field and even once from inside a large brick community building while doing an FT8 demo.
Loops are a brilliant solution when you have:
- QRM from local noise sources,
- limited space to deploy an antenna,
- or need a very low-impact and small footprint antenna (very handy for those historic and archeological POTA sites).
The trade-off, of course, is that they have a high “Q”–meaning very, very narrow bandwidth. Basically, anytime you move frequency? Yeah, it’s time to re-tune.
The environment around a loop can also have a pretty significant impact on your ability to tune it as well. For example, metal support structure in a building, window frames, metal poles, vehicles–anything like this nearby can have an impact on your ability to tune a loop and obtain a low SWR.
It’s for this reason I use them so little in the field–where I live, wire antennas are so easy to deploy and use.
But sometimes loops are the perfect tool, so knowing how to efficiently and effectively use them is important.
The F-Loop packed
I thought I had posted an activation video using the F-Loop, but looking back I realize I have not.
Yesterday, I decided to pack the F-Loop in my larger Spec-Ops Brand T.H.E. Pack which can easily hold the entire loop, folding tripod, and antenna analyzer.
I always fully set up an antenna before packing it in a new pack just to make sure I’ve included all components. I used this as an excuse to improve my loop tuning skills by intentionally chasing POTA stations across the HF bands. I worked all of the stations I hunted (five, if memory serves).
Twice I obtained a brilliant match just by using my ear (listening for the HF band noise level to increase as I tuned the variable cap) and the rest of the time I turned to my RigExpert handheld analyzer to find a low SWR.
I’m looking forward to taking the F-Loop to the field soon just to see how well it performs. After my practice today, I do believe I’ll keep the antenna analyzer packed with the loop–it makes it so easy to find a good match.
I find the F-Loop a wee bit easier to tune than my W4OP loop. The W4OP loop is also a brilliant loop if you can find one–I recently gifted mine to a friend. Here’s my review from a few years ago.
I’ve used an AlexLoop once and was impressed as well. That’s another antenna I may review at some point.
Commercially-produced mag loops are pretty expensive though. I do plan to build a 20M mag loop antenna before end of year. They’re surprisingly easy to build if you have a good variable cap.
Curious how many of you regularly use mag loop antennas. If you do, what make and model? Or is your loop homebrewed? Please comment!
22 thoughts on “Honing my mag loop tuning skills”
I bought an Alexloop about seven years ago and have used it in the field many times. It’s particularly handy for those times when I need to set up quickly and keep to a small footprint. I often carry the Alexloop along as a backup antenna.
When I’m using a rig without an SWR indicator, I use a small resistive bridge with an LED indicator. That helps with the tuning and gives some protection to the rig’s finals.
With their small size and proximity to the ground, loops never cease to amaze me.
Craig: Your resistive bridge with LED indicator…is that a kit? If so which one?
I used a kit from qrpkits.com and packaged it in a small aluminum box that I had on hand. It looks like that kit is no longer available, though. The documentation is still on the website, so it’s easy to homebrew one. I’ve built a few from scratch over the years. You can also Google “Tayloe Bridge” to find schematics.
I found that I have to reduce the power on some bands with my TR-35 to get the LED to fully extinguish at resonance.
72, Craig WB3GCK
Hi Tom…with a KX2/KX3 I do the following…(This may look complicated…but it is truly ‘easy-peasy’ and works great…and best of all, no SWR meter needed in the field 🙂
1. Set TUN PWR to 1-watt (I leave it there “forever”)…this overrides your transmit output power for QSOs so that while TUNING the higher SWRs won’t hurt the radio’s finals…
To transmit with a Mag Loop:
2. Set Menu ATU MD to Bypass (mostly only for use with Mag loop antennas)
3. Adjust the variable cap on the mag-loop for maximum noise
4. Hit the TUNE button on the KX2/KX3 to send a CW carrier (at the TUN PWR setting of 1-watt).
5. ‘Gingerly’ nudge the mag-loop variable cap one-way or the other and watch the SWR meter on the KX2/KX3 until you get 1:1 or so…
6. Hit the TUNE button to stop the CW carrier
7. Transmit while using the mag loop
8. Repeat above steps 3-7 until you QRT for the day…
9. When all done….reset menu ATU MD to Auto
Some of this process was derived in part from the “TUNE” information found on page-19 of the KX2 manual (page14 in the KX3 manual)…
Jim / AC3B
Thank you, Jim. That’s a sound procedure!
Thanks, Thomas and Craig. I am using an Alexloop with good results when _hunting_ portable stations in CW here in Europe. Most of the time I operate this antenna indoors and especially on 40 m it is efficient for getting rid of local QRM.
BTW….if anyone is interested in my W4OP loop (I have both tuning capacitor boxes and the remote tune device)….all inside a Pelican case….then please contact me off-line email…
Hi Thomas and All
Mag loops can be very useful when operating from areas where there are no “natural” antenna supports. Most of my /P operating is from areas of salt marsh where there are no trees.
I have three mag loops, an Alexloop and two home-brews, one of these is the same size as the Alex loop and is used where I don’t need a collapsible antenna (air travel). I also use a bigger Home-brew loop which is four feet in diameter and more efficient than the the Alex loop. The bigger loop is a bit of a handful to support when deploying. I use a discarded golf trolley as a mobile support.
Like vertical antennas mag loops can use the “salt water amplifier” effect, and when operated very close to salt water have very low take off angles. I find I can easily work DX with 10W of SSB. If I can hear them I have a good chance of working them.
Hear is a tube video of me working across the pond with the big loop and my “old but trusty” Icom 703.
Incidentally the area I am operating from is one metre within the boundary of the Colne Estuary SSSi and probably is a POTA site – several other places on this SSi are definitely POTA
73/72 to all
Interested in your 20m loop build. Do you have the variable capacitor yet…if so please share detail of which one you have.
Hi Joe. Yes I still have the loops and their tuning arrangements. I have in the past sourced my tuning capacitors from flea markets, hamfests etc. Having purchased them I check them at home capacitance range and general condition. I then choose a suitable variable capacitor for the size of loop I am building from these.
Maybe you could email me direct at [email protected] if you have specific querie
73 Tom G0sbw
Would definitely be interested in a review of the Alex Loop, it would seem the tuning LED could replace the antenna analyzer for an even lighter equipment packing.
Looking forward to your mag loop activation and review of the Alex Loop.
Btw: The separate Alexloop tuning LED as it seems works with all similar loops. The newer version of the Alexloop has the LED built into the tuning unit.
As always great information.
I bought an F loop V2 and have not used it much. Need to break it out. I also use my TX-500 as it has a built in network scan, meaning it will sweep the band and show me a graph of the SWR. I find that very handy.
Now I need to getmy loop out. And thanks to you may be adding to my stable of packs, and I blame you! 😀
I am heaidn gup your way in a few weeks and will bring the Hendricks with me.
Thanks for you posts!
Ha ha! Sorry to be such an enabler, Kent. 🙂
Sounds great regarding the trip this way. I look forward to it. As soon as you have the dates, let me know so I can find the time in my calendar.
I think the F-Loop pairs brilliantly with the TX-500. I used that pairing at a very early activation with the TX-500, in fact.
I have an MC-20 loop by OM0ET. On radios without an SWR bridge, I use a QRPguys tuning indicator to get it dialed in. I also built a K7QO noise bridge for the same purpose.
I have mostly used the loop at home–it’s a little bulky for my field operation style, but your post has inspired me to think about dragging it up a mountain some time.
Replying to myself here–this post inspired me to pull my mag loop out and play with it a bit. Using the noise bridge on a radio with a spectrum scope or waterfall is pretty interesting–you can actually see the resonant point move around as you adjust the capacitor. Makes it really easy to narrow in on 1:1 SWR.
Hello Tom, I use my homemade magnetic loop from 3-30 MHz. Normally this isn’t possible. But my system can be extended by a second loop for 80m and 60m. I also made a system with a switch and a piece of coax to tune on the 10m band. The antenna is purely made through experimenting and practical use. I took me years. Latest build/experiment can be read here: https://pe4bas.blogspot.com/2021/09/magnetic-loop-antenna-my-practical-mods.html
73, and good luck building your 20m magloop. Bas PE4BAS
I have the AlexLoop with the built-in LED. I do like it a lot. But the tuning control is a bit touchy. I’d like to replace the knob with one of those multi-turn knobs (I think that’s what they’re called) where one turn of the knob creates maybe a one-third turn of the tuning shaft. This would make it much less touchy. Anyone know where I can get a knob like that?
I think they are called vernier tuning dials. I also have an Alex Loop. I think it’s great, but I like your idea to improve it.
I have the Alexloop and results have been mixed. Lately I have been using a Nano VNA to tune it. The NanoVNA SWR is real time and changes as you tune. It is also small and light which is great for POTA. I also use it with my Emtech ZM-2 to check tuning.
I recently bought the W2LI Loop antenna and am figuring it out. Because of the necessity of retuning every few kHz, am I right in thinking more people call CQ on a loop such as this than do hunt up and down the dial?
I think most field activators do use it in situations where they’re the activator and calling CQ. Mag loops work for hunting stations, too, but just require extra care re-tuning each frequency.
Mag loop are also ideal for modes like FT8/FT4 where all of the action takes place in one narrow frequency range. Of course, key is to make sure your loop can handle the power output and duty cycles.