John Portune, W6NBC, on Mag Loop Antennas
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- čas přidán 29. 07. 2023
- Prolific ham radio researcher and inventor John Portune, W6NBC, spoke to W6SD, the San Fernando Valley (CA) Amateur Radio Club in July of 2023 about construction and use of the (incorrectly named) magnetic loop antenna.
- Věda a technologie
interesting and insightful, thank you very much !!
Thank you very much. 💪🇺🇸👍
After 40 years of fooling with loops, I thought I knew everything I needed to know, but I was taking notes on this presentation. :)
Amazing info. Thanks!
Wow…much needed info!
for testing the loop with a field strength meter/magnetometer , etc in the far field.
The inverse square law states that for a point source of waves that is capable of radiating omnidirectionally and with no obstructions in the vicinity, the intensity I decreases with the square of the distance, d, from the source.
On the foil tape. Do you need to do anything about the adhesive where the tape overlaps? I don’t think that tape is made to specifically be conductive so the adhesive may not be conductive either and the overlapping portions may not be making a good connection.
The adhesive layer is very thin, and so the overlap has such high capacitance that it is effectively a short at RF
I wonder what *edge* skin effect is? I cannot find any mention in my sources- . The antenna at 55:43 did not look too bad for me. Except very thin see through conductive material.
There is no "edge" skin effect: skin effect is the result of the current trying to get as far away as it can from other parallel currents. This means that to take advantage of skin effect, your conductor's cross-section needs to be as close to perfectly circular as possible. If it is square, then the effect of the currents being repelled from each other is that all of the current goes through the corners of your square conductor.
Now I'll go off the beaten path into conjecture on my part: if you do a multi-turn loop, I believe the coils should be arranged to that together they form a cylinder around their center. Once your into multiple turns, the current will all be on the outsides of those turns, to the extent that maybe you only need to put the aluminum tape on the outward-facing side of the PVC/ABS/PE pipe. I'll need to think about this further.
This is good info but there seems to be zero actual builds or examples detailed which are using these ideas on the internet to see if they actually work or not.
It would be easy to perform quantitative comparisons instead of simulations...
John, your first video you specify a skin debt for 40 meters to 1.2 and on this video you change to 3x at 3.6 mils. In determining thickness of aluminum or cu tape the aluminum should be at least 3.6 mils thick for 40 meters? May I also ask if this loop will work with an sdr rspdx as at this point I will only be using it to receive not transmit?
Is there a final build for this?
Excellent article. Perhaps the mag loop should just be referred to as a closed loop or simply a loop. I’ve been in a on again off again process of building a loop with 1” copper (a freebie throwaway) that works out to 48” diameter. I’m rethinking now to go to the larger diameter. I would like a loop that’s relatively efficient on 40 that can still be hauled around. And being able to operate close to the ground is a plus. Thanks for the ideas on tuning capacitance. And I will look into the use of PEX as well. 73
Does anyone know the fitting for the 1"pvc tuning pipe? Is it a cap thats drilled or a coupler?
If square gets you more area, then wouldn't building a square shape loop but with 3x3 or 2x2 boards and covering with aluminum tape for more surface area of the loop?
No. As John says near the end, if your conductor is flat, then the skin effect moves all of the current to the corners of its shape. The cross-section of your conductor still needs to be circular to get the best conductivity.
Hi, I have had my license for a long time, mostly for 2M work with the local network for hurricane shelter emergency work. But now I am retired and going to move into a bus I am converting and sell my condo I have been watching "mag loop" antenna development and was considering one for the roof of the bus and one on the roof of my jeep. But I had been figuring on laying them horizontally for nondirectional use but you are the first person I have heard say they wont work horizontally. I was just wondering why they won't work as well horizontally as they do vertically. The radiation pattern for the loop would be nice if they did work horizontally. I can make them tip up and put a rotator on them. But that would make them only usable when not on the road.
Mainly, it's because the magnetic field they produce is through the axis of the loop. So if you have the loop oriented horizontally, the field is going into the ground and straight up into the air. Pay no attention to what John says about there being no such thing as a "magnetic loop antenna". Both electric field and magnetic field transmissions end up being the same (i.e., a balance of electric and magnetic fields) once you're a few tens of wavelengths away from the antenna, but in the near field, these small loops (i.e., diameter
Does anyone know the title of the "IEEE Study" he refers to on not matching the receive only antenna?
Thoughts on using aluminum downspout material for this project? Paint can be removed for connections
About the efficiency discussion: 50% loss of power is -3dB. One S-unit is 6dB. So 50% loss in antenna is half S-unit on receiver. Of course if both sender and receiver are using same kind of antenna with 50% efficiency then the losses are combined to 6dB thus one S-unit.
Yes, but you don't have any control over the other person's antenna. It's better to think of what you're sending as effective radiated power, which takes YOUR antenna's efficiency into account. What's going on at the other end is the other guy's problem.
I don't know much about loops, obviously, and I am confused about how to feed this antenna? what is the center conductor of my coax attached to and what is the shield connected to?
Why not do a horizonal loop?
for everyone's perusal