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.
Best presentation of magnetic loop antennas! I had the idea to get flexible pvc exhaust hoses with an inner aluminum layer. 3'' is available at amazon. Anyone tested this material?
If using the loop as a receive only loop are the skin effects still significant factors, ie, using a flat aluminium strip as the conductor for both loops. I would like to build a loop antennae and wonder if I need to take all the factors that John details in this presentation into my design but if the loop is receive only (I wont be transmitting at all) so I don’t want to put effort into anything that’s not needed, so how would a receive only loop differ from the above. I still like the idea of the capacitor tuning and assume this is still a critical factor I need to take into account in my build. I am a complete beginner at this so any feedback would greatly be appreciated
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.
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?
Have a exhaust hose with a 15 micron Al layer. Know it's not very beefy esp. for longer waves. Hose diameter is 3'' btw. Will I get issues which QRP 5 W or is this problem independant from power? 73
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.
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?
Great article. Perhaps I misunderstand the application of the aluminium tape. Rather that cut the pvc elbows and line the inside of them with tape, is it not possible to simply glue the elbows to the frame and then wrap the frame with the tape overlapping the elbows and the frame with two or more wraps resulting in continous continuity.
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
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.
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.
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.
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
After 40 years of fooling with loops, I thought I knew everything I needed to know, but I was taking notes on this presentation. :)
Thank you very much. 💪🇺🇸👍
Amazing info. Thanks!
interesting and insightful, thank you very much !!
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.
Best presentation of magnetic loop antennas!
I had the idea to get flexible pvc exhaust hoses with an inner aluminum layer. 3'' is available at amazon. Anyone tested this material?
If using the loop as a receive only loop are the skin effects still significant factors, ie, using a flat aluminium strip as the conductor for both loops. I would like to build a loop antennae and wonder if I need to take all the factors that John details in this presentation into my design but if the loop is receive only (I wont be transmitting at all) so I don’t want to put effort into anything that’s not needed, so how would a receive only loop differ from the above. I still like the idea of the capacitor tuning and assume this is still a critical factor I need to take into account in my build. I am a complete beginner at this so any feedback would greatly be appreciated
Wow…much needed info!
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
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?
Have a exhaust hose with a 15 micron Al layer. Know it's not very beefy esp. for longer waves. Hose diameter is 3'' btw. Will I get issues which QRP 5 W or is this problem independant from power? 73
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.
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?
I have the same questions and been looking over the internet for days, without finding the answer.
Today i emailed John, so lets hope for an answer ;)
Great article. Perhaps I misunderstand the application of the aluminium tape. Rather that cut the pvc elbows and line the inside of them with tape, is it not possible to simply glue the elbows to the frame and then wrap the frame with the tape overlapping the elbows and the frame with two or more wraps resulting in continous continuity.
Thoughts on using aluminum downspout material for this project? Paint can be removed for connections
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 fitting for the 1"pvc tuning pipe? Is it a cap thats drilled or a coupler?
Does anyone know the title of the "IEEE Study" he refers to on not matching the receive only antenna?
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.
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...
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.
Why not do a horizonal loop?
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
for everyone's perusal