When I built my 10M loop, I used this calculator:

I liked this calculator, since it provides approximate voltages the cap will see and I could play with the figures to see the outcome.

Depending on the rf power, you could see several thousand volts at the cap.? They also have a capacitor calculator, you could use that to design a cap.

You could use coax capacitors, high voltage caps, air variables, trombone style, or vacuum variables, just to name a few.? Search you tube, there are a ton of examples.

I am feeding the loop with a toroid and 3 turns of #12 wire.? Similar to VK6CS in these videos:

To connect a motor to the cap, use some kind of insulated shaft coupler to keep the high voltage off the motor.? Make sure to bypass the motor terminals with a 0.1uf cap to try and keep the rf out of the motor.? I would suggest a geared motor, ?something with a low RPM.? You could vary the voltage to the motor, to control tuning speed.

Hope that helped some.

Marco - KG5PRT?

On Jun 21, 2017 1:17 AM, "John Smith via Groups.Io" <johnlinux77=[email protected]> wrote:

I have some plans and ideas, but thought I should consult with the smartest group of people I know. Can I use zinc plated hardware with aluminum roof flashing? How to attach a arduino stepper motor to caps rotor shaft? Cheat on the loop by covering a hula hoop with aluminum foil? And I still need a antenna tuner after tuning the cap for resonance, Right?
Have any mag loop calculators, or instruction sites. Hopefully I will find more than I've seen so far.? Good instructional homebrew videos on youtube are great too

Thanks in advance de KG5KYJ

Here are a couple of pdf articles that might help.

Marco - KG5PRT?

On Jun 21, 2017 8:34 AM, "Michael Hagen" <motdog@...> wrote:

I have never heard an outside signal on my bit40.? Testing with a signal generator I get signals down to or below 10uV?

I have no antenna, but a wire out the door brings in nothing but a little more noise.

To make others happy, I could hide the loop when not experimenting.? No one I know nowadays knows what a Ham is!

I am gathering parts for a loop.? I got 8 3/4" 45 Degree "El".? I am going to get 2 10' sticks of the thinner 3/4" copper pipe.

If I cut to 8 pieces, there will be 2 1/2 ft. per section.? So the loop should be 6 ft or so.

I found an online store an got the copper fitting a lot cheaper than the Home Depots around here.? About 1$ a fitting.

There is an L and M designation.?? For the drive loop, the hardware stores sell rolls of 1/4" copper tubing.

To get started just to receive, the little Polyester AM radio capacitors will work.? With a real high Q, I will just tune for noise (I hope).

I have seen people put big wire or coax in Hula Hoops. But not Tin Foil?? To maintain High Q, you might need less resistance?

If I have any results that warrant the expense, I will buy a vacuum variable.? But the $3 AM radio variable is used everywhere and
in a lot of low power Ham projects.

Mike, WA6ISP

On 6/21/2017 12:08 AM, M Garza wrote:

When I built my 10M loop, I used this calculator:

I liked this calculator, since it provides approximate voltages the cap will see and I could play with the figures to see the outcome.

Depending on the rf power, you could see several thousand volts at the cap.? They also have a capacitor calculator, you could use that to design a cap.

You could use coax capacitors, high voltage caps, air variables, trombone style, or vacuum variables, just to name a few.? Search you tube, there are a ton of examples.

I am feeding the loop with a toroid and 3 turns of #12 wire.? Similar to VK6CS in these videos:

To connect a motor to the cap, use some kind of insulated shaft coupler to keep the high voltage off the motor.? Make sure to bypass the motor terminals with a 0.1uf cap to try and keep the rf out of the motor.? I would suggest a geared motor, ?something with a low RPM.? You could vary the voltage to the motor, to control tuning speed.

Hope that helped some.

Marco - KG5PRT?

On Jun 21, 2017 1:17 AM, "John Smith via Groups.Io" <johnlinux77=yahoo.com@groups.io> wrote:

I have some plans and ideas, but thought I should consult with the smartest group of people I know. Can I use zinc plated hardware with aluminum roof flashing? How to attach a arduino stepper motor to caps rotor shaft? Cheat on the loop by covering a hula hoop with aluminum foil? And I still need a antenna tuner after tuning the cap for resonance, Right?
Have any mag loop calculators, or instruction sites. Hopefully I will find more than I've seen so far.? Good instructional homebrew videos on youtube are great too

Thanks in advance de KG5KYJ

On Jun 21, 2017, at 11:22 AM, John Smith via Groups.Io <johnlinux77@...> wrote:

I like the calculator, i've seen it before but lost it and have been using a software version by KI6GD. I have it bookmarked now, thanks.

What I am seeing is a 40M band loop with 90+% efficiency, needs 30 feet of 2" copper tubing.

I currently have RG8X coax on a VHF ground plane antenna which gives me about 30% loss. It's a different system than BITX'ers and HF ops use, but comparatively speaking, if a mag loop has that much loss on 40, I wouldn't bother making it.

I am really getting the impression that mag loops are better suited for 20 and above. Does anyone concur?

The size of loop required above 20 m for any kind of transmission efficiency makes their use highly inefficient. I think they are neat antennas, and interesting in many ways, and I have made and used them myself, but I think of them, literally, as a last resort. Almost anything is better than a mag-loop; I know some people have success making qsos with them, but operators also make qsos with dummy loads. Even a short wire and counterpoise attached to some coax and a balun will work much better than a tuned loop. I know there will be people who reflexively respond to this with their own tales of amazing results, but a larger, more efficient antenna will almost always outperform a smaller, less efficient antenna.

I think that was well said all the way around. What do you think of them as receive only antennas, both as a two antenna system, and just for receivers only? If anyone is wondering what I mean by two antenna system, think about the Beverage antenna as receive only, and something else for transmit. This comes to mind because of the loops directivity and high Q, aka, less noise and QRM reception. So, is it equally inefficient at reception??

On Wed, Jun 21, 2017 at 12:24 pm, Simon Thompson wrote:

The size of loop required above 20 m for any kind of transmission efficiency makes their use highly inefficient. I think they are neat antennas, and interesting in many ways, and I have made and used them myself, but I think of them, literally, as a last resort. Almost anything is better than a mag-loop; I know some people have success making qsos with them, but operators also make qsos with dummy loads. Even a short wire and counterpoise attached to some coax and a balun will work much better than a tuned loop. I know there will be people who reflexively respond to this with their own tales of amazing results, but a larger, more efficient antenna will almost always outperform a smaller, less efficient antenna.