Part 2 Quest for the best mag loop antenna
ฝัง
- เผยแพร่เมื่อ 13 ม.ค. 2023
- A new method of setting the frequency (tuning) is revealed. Low SWR on 10M thru 40M. High efficiency design. A new type of variable capacitor is explained. What is a power booster? what is "Q" actually?
Here is a link to part 1 of this video.
• Quest for the Best Mag...
Here is a playlist of 3 videos that anyone interested in mag loop antennas must see.
• Magnetic Loop Antennas - วิทยาศาสตร์และเทคโนโลยี
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excellent description Jim... you are a great instructor/teacher...and communicator... thank you...
Thanks for your kind comment.
Jim, thank you for all of the great information and work which went into your videos on Magnetic Loop Antennas. I've been licensed for coming up on 50 years soon and had completely missed this antenna, had been active in EME with big phased arrays and power for a long time, but not on HF until recently moving into an apartment and needing something small.
Thank you for your comment.
Thanks so much Jim. Your explanation covers the basics I needed to get a better understanding of the design considerations for the mag loop. Great overview and good visuals.
Thanks for your comment.
Your use of an oscillator to aid tuning is brilliant. I have not come across this before. It reminds me of grid dip meters and netting for zero beat in the old days of AM on top band 🙂
Thanks for your comment.
Brilliant!
Very interesting, thank you
Thanks for your comment.
Great project ! Could you talk more about the fine tuning circuit you designed . This sounds like it could be super helpful
I am still working on that. I hope to have a video about it soon. Thanks for your comment.
Dear Jim, watched with great interest your clear explanation of the mag loop antenna!Am very interested in your follow-up videos, for example whether you built the variable air capacitor yourself. A year ago built a mag loop antenna from 15 millimeter copper water pipe 1 meter diameter with a variable capacitor 25 - 225 pF. This works from off the 19 meter to 20 meter band.
Jim, Good luck on this fine project!
73, Theo
Yes I built the capacitor myself. It is an unusual design. It is very difficult to get a capacitance low enough for 10M and high enough for 40M in the same unit. Thank you for your comment.
Thank you for the video! I am also building a magnetic loop antenna. It is made out of a 50mm PVC pipe that is covered with aluminum tape. The capacitor is of the trombone type. It will be interesting to see how it performs.
I have found that PVC is a poor capacitor dielectric material. I tried to make a capacitor using PVC and it got hot.
@@Jimscoolstuff I checked and the tube is not PVC but polypropylene. I wonder if it's better or worse than PVC?
@@ponttokamera I don't know about polypropylene. Please let us know if it works. Both Teflon and polyethylene are used as insulators in coax cable, so these should be good capacitor dielectrics.
thank you Jim!
Thanks for your comment.
Jim, I was just about to build a PVC tube design following John Portune's plan when I came across your video. I really like your use of rectangular aluminum tubes. I know your work is a design in progress but can you please tell me if 5 months after your video, you still find these four-foot-long 2" by 1" aluminum tubes to be a recommended approach? Thank you.
Yes, I think the rectangular tubing is sturdy, light weight, easy to work with, and very efficient electrically.
I got diverted by EFHW projects (I made several videos) but plan to get back to the loop antenna soon. Thanks for your comment.
Thanks for an excellent presentation ! It motivates me to experiment more with loops. A question about your second equation for Q=BW/Fc. It it upside down ?
Yes it is inverted. Thank you for pointing this out.
Exelente video
Thank you for your kind comment.
Jim have you completed the mag loop antenna? Has it functioned well? I live in a HOA and would want to put it in my attic. Do you have the final build specs? Thanks
Thanks Jim for all the informative and very valuable HAM radio videos ! question about this designed Mag Loop antenna, what is the range of the self-built variable capacitor? We live on an apartment then fortunately a Mag Loop antenna is compact enough to work HF bands. Thanks! Kind regards from the Netherlands, Theo 73, PA0HTY.
The capacitor range is 7 pF to 180 pF. The hardest part of the design was getting down to 7 pF for the 10m band.
I'm seeing your video right now and I'm not sure about skin effect on rectangular tubing is like on round section.
May be the current is flowing through corners only, which is reducing a lot your loop efficiency
How did you construct the method of antenna tuning without using your transmitter?
Some type of oscillator circuitry? Thanks for making these videos.
Yes you are correct. You can turn a high Q loop into it's own VFO. This is proving hard to do on all bands (10M-40M). I am still working on this and i hope to have it perfected soon. Thanks for your comment.
Hello! Thank you very much for taking the time and effort to produce this high quality video. Very instructive indeed.
If you have time, could you please make another video showing in details how the "FEED loop" works in the megloop you are building?
I see you have connected one leg of it (towards the left-bottom corner) to the MAIN loop? Can you explain a bit how it works?
I thought (also from the PART 1 you did earlier) that the FEED loop was physically disconnected and only magnetically coupled to the MAIN loop. THANK YOU!
Yes I am planning to make videos on the capacitor, the capacitor drive system, the coupling system, and how to turn the antenna into an oscillator ( a VFO) for tuning. It turns out that it is impossible to drive the main loop with a small fixed position coupling loop and achieve a very low SWR on multiple bands. For this reason I went with the coupling system that is shown. Thank you for your comment.
@@Jimscoolstuff thanks a lot!
I have one curiosity regarding your "rotating FEED loop" idea.
Basically, rotating the FEED loop, you are adjusting the "projected area on the MAIN loop", as in cosine(theta). Correct? At the extreme, when the feed loop is rotated by 90degrees, you get 0 coupling as if the area was 0 (as in cos(90) = 0).
This is a clever method for adjusting the area of the FEED loop!
However, does it come at at an efficiency cost? After all, the energy radiated by the FEED loop orthogonally to the MAIN loop is wasted. Correct?
Thanks!
@@therfnoob7697 Very good question. Before rotating there is a high SWR, so energy was wasted by reflection into the feedline. After rotating for a 1:1 SWR all the energy is radiated. It may be more like a phase shift than a direct area projection. Thank you for your comment.
@@Jimscoolstuff thank you for the answer. My point is that 1:1 SWR only means that 100% of the energy from the radio is going to the antenna, but *NOT* that 100% is radiated out to the air. Some energy can be wasted (by heating of elements, or magnetic/electric field losses). I suspect rotating the FEED loop away from the MAIN loop plane is reducing the actual radiated power, due to magnetic field losses from LOOP to MAIN. But I am not sure. It would be interesting to check this out. Keep up the great work!
Addendum: in the extreme case when the FEED is 90degrees (i.e., perpendicular) to the MAIN loop, there should be (theoretically) zero coupling between the two loops, and therefore zero radiated power.
Hi dear Jim, I've been following your work since the other video. I was concerned about the small electrical connection surface (not the structural one) in the corners of the square loop. I see that you have now added a second angle on them. In a similar project I'm working on, I'll also add flat side brackets at that location to cover all four sides of the connection. Is it possible that you give us a comment or reference on how you have built the controller with a fine adjustment potentiometer? Thank you very much in advance and for your excellent videos. LU1DYI, 73!
(I mean how can I turn the circuit into an audible oscillator)
The second angle bracket was added for mechanical reasons, not electrical contact. By using position feedback for the capacitor the position can be set with a position reference from a pot. There are 2 motors in the drive unit, One is operated from the coarse (band select) pot. the second motor (fine adjust) rotates the base plate of the course motor. I am not done improving this arrangement as yet. I will show more in future videos after I am satisfied with the operation. Thank you for your comment.
@@Jimscoolstuff thanks so much !
@@Jimscoolstuff Hello again Jim, maybe you can guide me on the issue that worries me the most. How did you convert the LC circuit into an oscillator via the switch, so that you then perform the fine tuning motor movement based on what you hear? What did you use to turn it into an oscillator? (I understand how to move stepper motors, not my question) Can you share something about your oscillator so that I can study the subject ? Your help would be greatly appreciated. Again thank you very much !
@@danielsolowiej This is not very clear in the video, I will do it better job in the next video. The sound is coming from a radio tuned to a particular frequency that you want to transmit on. A high Q, L-C circuit (the mag loop) is made to oscillate at its resonant frequency. The mag loop is then a VFO (variable frequency oscillator) that can be tuned to the receiver frequency by adjusting to a zero audio frequency (zero beat). The switch activates a relay that connects the oscillator circuit to the loop. In the final design the switch will be replaced by a pushbutton. This will make it less likely that someone will transmit when the oscillator is connected (poof).
Jim, good morning. that thin horizontal copper wire is that part of the gamma match? And how is the normally center capacity of the Gamma Match formed? Thx. Theo PA0HTY
The copper wire is not a gamma match it is just a coupling loop. In other videos where they use a round main loop, they typically use a smaller round loop to couple power to the main loop. Thank you for your comment.
Thank you so much Jim. Can you please le us know the value of variable capacitor
The range of the capacitor is 7.7 pf to 240 pf.
@@Jimscoolstuffhow do you go so low?
Great information. Do you know if anyone has tried a magloop curtain array such as 3 loops wide and 3 loops high, probably in series to bring up the impedance?
No I don't know of any work being done on this. Probably too costly for home experimenters.
I like the idea of using box metal for the loop. But the capacitive coupling between the plates on the corners doesn't improve the Q. That requires a reduction of purely resistive loses. I'd suggest having the corners welded to maximize the Q, assuming you would need it. You probably don't. If I build a similar loop I'll shoot for a very high Q and will get the corners welded. I'm in an apartment surrounded by noise sources, without the ability to put an antenna outside, so I need a very small, very high Q antenna for use in the apartment or out in the park.
Sorry type error 10 m- 20 m band