Boost your Magnetic Loop Antenna on 20M 40M 80M - Chameleon F-Loop 3.0 and others
ฝัง
- เผยแพร่เมื่อ 17 ก.ย. 2024
- Hi this is Frank
In this video I show how I have increased the size of my magnetic loop to improve transmit performance and may be give you ideas on how you can improve your own magnetic loop.
VE2FGJ
Usually we have small portable loops that are convenient, but the efficiency is limited mostly on transmit.
Having a Chameleon F-Loop 3.0 with the standard 102 in loop and the 146 in Booster cable, I wanted to improve the transmit efficiency by increasing the loop size.
With the 66pacific.com web site (link is in the description) I calculated the efficiency of the
Standard 102 in loop to be: 52% on the 20M band
Booster 146 in loop to be: 76%
I had the idea to join 2 x 102 in loops together but instead of doubling the loop I would use it as 1 single big loop
The length is 205 in and the efficiency is: 90% on the 20M band
Link: www.66pacific....
Now let’s look at the 3 loop sizes on 20M 40M and 80M
With the 102 in loop I got: 52% 9% 1%
With the 146 in loop I got: 76% 22% 3%
Lastly with the 205 in big loop I got: 90% 44% 8%
When using a bigger loop like the 205 in as a single loop, we immediately find that:
1. The supplied telescopic mast is too short, so we replaced it with a 5 ft Monopod, which is normally used for cameras and adapt it to fit using several 3d printed parts, nuts and bolts. This allows to use the smaller loops as well as bigger loops.
2. The supplied inner loop is too small, so we made a new inner loop using aluminium, the approximate ratio is 1/5th (or 20%) of the outer loop, in this case it is 13.3 in. Using several tools, we were able to reproduce a inner loop that looks very much like the original.
Magnetic loop contacts with S51DX and E71A.
Using the 205 in loop provides a wider bandwidth and is also easier to tune. After several successful transmisions up to 30W in CW we decided to get ride of the coupling barrel in between the 2 loops to make 1 single cable.
This is important, What we discovered with this new cable is, we could not get a good SWR above 10W, that puzzled us for a while, after several tests we put the previous cables back with the barrel coupler and yes the SWR was good all the way to 30W in CW.
We eventually realized that both PL-259 connectors were making contact on the inner loop, that certainly changes the coupling behaviour. I am not an engineer, I cannot explain how or why, but it does work much better if the outer loop makes contact with the inner loop with this scenario. May be some of you watching can comment and explain why this is happening.
With a bigger coaxial loop expect that the wind will bend the coax and may de-tune the coupling as it wobbles, my solution is to orient the loop 90 degrees perpendicular to the wind direction, that pretty much minimizes the wobble.
In conclusion, you can improve the efficiency of your magnetic loop by increasing the loop and the inner loop sizes, calculate what best fits your requirements, experiment and I would love to see your own experiences or questions in the comments below. Good luck on your build.
This is Frank signing out, thanks for watching! 73
Authors: VE2FGJ and VE2GIQ
Notes: Stepper Motor is dual shaft NEMA 17, radio is an ICOM IC-705 with RM Italy MLA-100 Amplifier, Mag Loop Controller is home made with a Teensy 3.5 Micro-Controller and HC-05 Bluetooth, the screen is a Nextion touch screen, all is programmed in C (Arduino), includes an Auto-Tuner, Pro-Active Tuner and multiples functions, it is 4400 lines of code and is built to use ICOM CI-V (via Bluetooth or Serial) to read SWR and VFO values, has been tested with IC-705, 7100, 7300, 7610. A SWR bridge was considered but we resolved to use the radio’s SWR meter (which goes up to 6.0:1) Not for sale, please do not ask for purchase.
The Goal of this video is to encourage you to increase your Mag Loop size, calculate your requirements, experiment and improve performances.
Building and optimizing is the spirit of Ham Radio enthusiasts.
73 from Quebec, CA
Music: Miami - Del
One of the best ham TH-cam videos I’ve seen. Clear concise explanation, no bs, great experimentation. Well done Frank
Hi AJ, Wow thanks for the super nice comments, I did spend too much time making this video... I am glad you liked it, hoping it will help others with their Mag Loops and experiment for better performances! 73 !😃👍
@@VE2FGJ absolutely this is really really cool stuff. I have a chameleon myself but haven’t used it much because of the inefficiency!
@@aj2isotadxing Please try boosting the loops sizes, it can be impressive! Thanks 73!
Awesome video, Frank! You've given me some ideas for working with my F-Loop. 73 from VE3TWM.
That is great Tracy, thanks for the comment and good luck on your build! 73
Outstanding work Frank !
Can't wait for the next one.......
Thanks !
Hey Gilles, thank you very much, I appreciate it! 73
Awesome video, thank you for this! 73's AL9G
Your are welcome thanks for the comment 73!
Excellent 💯🎸🎙👍
Thank you glad you liked it! 73!
Great video. Most helpful thanks.
Thank you John, glad you like it!
Super vidéo! J'adore ma FLOOP 2.0. J'ai le compensateur également. Elle me permet d'utiliser mon kit dans la maison. Pratique en apartement en ville. J'avais pensé doubler la longueur, mais je ne l'ai pas encore essayé. Le diamètre de l'élément du loop semble aussi affecter selon ce que j'ai vu. 73 VE2IES
Oui le Inner-Loop doit etre 20% du Outer-Loop, le calcul est important. Content de voir que tu apprecie ta F-Loop 2.0 Super et merci pour les bons commentaire! 73
This is a great video. I was curious to see how much better a bigger loop would affect transmitting and receiving. I wonder what the results would be if you could replace the coax with 1” tubular aluminum.
I believe using a 1 inch tubular would increase the bandwidth, but a RG8 vs a 1 inch tubular is not much difference, some have tried with 4 inches tubular, I do not have those results. My 1st instinct is overall size matters more than thickness, but you can try and see and may be share your findings? Great question, ask for asking!
thanks Frank great info my loop just arrived today 73 Nigel ZL2SEA
Hi Nigel, awesome! Have fun! 73
Danke für das tolle Video.73,de Jozef OE1CJG.(S56CJG).😊😊😊
Been a fan of using longer and contiguous loops, rather than loops that are joined.
I use a T240-43 to couple my 20-40m mag loop. Depending on whether I use the compact 5m or the larger 8m loop, and depending on the band, it can take anywhere from 3 to 7 turns to get resonance and a 50 ohm match.
The coax touching the inner loop is like a centre tap on a tuned circuit with a transformer coupled second winding also with a centre tap….if that makes sense.
Hi Renaissance Man, Reference: "...like a centre tap on a tuned circuit" while I can imagine that, I have yet not found related materials to explain that kind of direct/indirect coupling that improve performances at higher power. Thanks for your comment.
@@VE2FGJwell you would be connecting the two circuits at the 0V points….assuming the feed to the loop was balanced…common mode choke on the antenna end of the coax would see to that
I try to tune my loops so they are at resonance with the smith chart in the middle showing the lowest Xl and Xc values I can dial up. I then note the impedance at that point and adjust the turns ratio and coupling to match.
Tighter coupling does _pull_ the resonance and impedance of the loop. You would loosely couple a free running LC RF Oscillator to the next stage as any loading would cause the frequency to move.
On my VNA I have SWR, Smith, phase and S21 Logmag. I look at SWR with respect to the Smith chart and phase with the idea that understanding the Xl /Xc components of the antenna at that frequency, let’s me know what I need to do to achieve resonance. (Logmag on S21 let’s me quickly check cables for losses)
What does the smith chart on your VNA show with the loop connected vs isolated ??
@@MidlifeRenaissanceMan Wow a lot of things I have not delved into, I wish I had a VNA to experiment with and without the center tap (barrel). I appreciate your detailed explanation, hopefully I will experiment more in the future. Thanks.
@@VE2FGJlate Christmas present. Get a NanoVNA. Best $50-150 you’ll ever spend. Seriously. If you’re working with any sort of antenna, a NanoVNA will show you all those important bits that you never think about.
Get one, check out one of the numerous videos on setting it up
You want to see SWR and the Smith Chart as a minimum. Smith chart tells you complex impedance so whether you’re too short or long as well as impedance at resonance.
My mate was screwing around with a fan dipole on 40 and 80m. Couldn’t get it to match up kept lengthening it but never better than 2.5:1
I came over. Stuck the NanoVNA on it with the smith chart. Because of the proximity of the ends to ground, it dropped the impedance. It was also resonant a little higher up, so we unfurled one end to lengthen it (he hadn’t cut just yet), and folded in the other end. This pushed the feedpojnt off centre and raised the feed point impedance at resonance. It was still a little short, but fine for the voice section of 80m with an SWR of 1.4:1 at the top end of where we can operate
Knowing the impedance and the complex impedance sorted that issue out. All with the $80 NanoVNA with the big screen I picked up used and replaced the battery to fix it’s random issues.
godt job 😀
Thank you, glad you like it! 73
The provided LRM-400 that come with the antenna are shorted at both ends! It’s probably why you were unable to tune with a regular coax cable.
We knew that and did short the cable's PL-259, we also shorted the F-Loop's SO-239 internally. Thinking back it may have been caused by not using a choke at the feedpoint, we used a 100 feet coax to stay away from the antenna. So many things to try...
Regular mag loop user here - the russian Spiderloop A100, several MFJ loops and home brew. I'm surprised it worked with the barrel connector touching the inner loop - I was always under the impression that they must not touch, rather they should couple inductively. Of course the very large loop won't work on the high bands, 10/12/15. Getting close to and more than 1/4 wavelength causes issues. Best performance is getting close to 1/4 wavelength but not exceeding it, but you probably know that. Large loop will work well on the lower bands
Yes at 205 inches the top band is 20M. For the barrel connector, may be the Power Compensator plays a role, in theory the inner/outer should not make contact. Glad to see you are using Mag Loops, thanks for the comment!
god job
great, I'm also pl working on making one in aluminum of 2x 520m there will be a video about it
That sounds great, I would like to see that! Thanks for stoping by!
Interesting would be measured! 1:2 BW on 20m with your 205" loop.
Yes, actually hard to measure, but bigger Loop = bigger Bandwidth and more efficient for TX!
hi.. thank you for the details you explained. can you please share the details of the Variable Capacitor too... I will have to be making one... hence some details will be surely helpful.
Hi, the F-Loop 2.0/3.0 capacitor is a 10-365 pF and 5-182 pF. There is a switch (A/B) we can toggle to switch between single/dual gang capacitance. To build a MagLoop I can suggest to use the least Capacitance and rather increase the Outer-Loop size to match the highest Band you will be using the most. As an example, in my latest video I chose a 205 in loop to use the 20M band with 90% efficiency. Bigger is better for the top Band you want to use, compensating with a Capacitor, results in lesser performances. Hope that helps. 73!
@@VE2FGJ Thank you for the tips. Makes things much clear now 🙂
Merci pour ce video, va2waw
Eric, merci pour le commentaire, content de voir que ce fut interessant 73!
Could you please let me know if you could use alum flat bar for the outside loop
Yes, a flat bar would work, but there will be differences. The thicker the outside loop is, the better it performs. With Google/Images you can search for Mag Loops and see all different types, size, shape, materials some use.
Hello! May I ask, which cable you used for the outer (big) loop? RG213-U ?
Hi! Cable is LMR 400.
Why are you using your antenna tuner with a mag loop?
The tuner is in bypass mode, it only shows SWR. The flickering you saw is because we did not use a choke at the feedpoint, some RF comes back.
Great video Frank, thank you, de ve7kkq.
Thank you John! West coast to East coast! Wow! 73!