Mag Loop Antenna info. 2E0ERO's version.

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BillC

Guest
Regarding tuning capacitors . It is worth remembering that for best operation in a resonant circuit the tuning cap. needs to have a low loss / high D , so the cap. needs to be kept perfectly shiny clean . Any dust forming on the capacitor plates would attract moisture which is the enemy of RF. I have several high quality level meters and the tuning capacitors are mounted in sealed enclosures . The repair manual for the HP 606 B signal generator states, if the output fails , the first thing to do is to blow air gently between the plates of the tuning capacitor . So obviously to remove dust . Perhaps some form of dust proof enclosure for a mag. loop tuning cap. might help to keep the performance up for longer periods of time .
Cheers .
 
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BillC

Guest
I am wondering about the possibility of making a tuning cap with two sets of fixed plates as it were , but with one set of plates mounted on a moving insulated frame such as teflon , so as to allow one set of plates to mesh with the other . The moving gang would have one more plate than the fixed gang . The moving gang would possibly connect to one end of the loop via a section of thin copper strap suitably pre- formed to allow for lateral movement of the tuning motion . The other possibility would be to hard mount the gang sections to the ends of the loop and allow the loop to flex slightly during the tuning motion as the plates move to and fro . Might be able to use teflon sheet for some of the support structure A capacitor made this way might be more efficient than some of the other more traditional methods . Bad luck about the "Gastite" it would have made a beaut Trombone capacitor .
 
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VK3ZYZ

Guest
I am toying with doing a PCB to drive a stepper for the antenna remote control.
It will be an Arduino Nano and a stepper driver like the A4988 modules commonly in 3D printers.
MagLoopControl.png

Only one input will be needed to set the home position then the steps are counted to keep track of the capacitor setting.
RS485 drivers for balanced comms and the cable will be an "Ethernet" 4 pair for power and comms.
Or would folk want a home input, a max limit input and an encoder input?
Comments are gratefully received.
 
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B

BillC

Guest
Looks interesting Denys I suppose there would be space on the b+ and coms . cables for multiple toroid RF chokes . I reckon that a remote controlled driver would have lots of uses too. Regards.
 
B

BillC

Guest
On the subject of antennas , check out " KE5EE testimonials" on youtube .
 
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VK3ZYZ

Guest
Doug, VK3YMG , pointed this out to me.
Squashing the mag Loop feed coils seems to improve things quite a bit.
 
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VK3ZYZ

Guest
Finally, I have started a mag loop antenna!
20211025_172058.jpg

There is a handy hole in the back yard where the previous owners had removed a rotary close line.

20211025_181854.jpg

This is a length of heliax that was in my shed.
Still to do is make some spacers for the sides, add a tuning capacitor and drive loop.
This antenna "design" was just the size of the roll. It will be interesting to see if it works, and on what bands.
 
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VK3ZYZ

Guest
Today I have made some progress!
20211026_Tuneable.jpg

Kevin's variable cap has been added for a test.

And here is the VNA plot...
20211026_VNA.jpg


I'm sure it could be better. maybe a larger and more circular coupling loop???
Something a bit stiffer so it can be a circle could help.
When the band opens, I may get to try it out :)
 

VK3ZYZ

Moderator
Staff member
This absolute encoder sounds like an ideal way to read an external device position, maybe a butterfly tuning capacitor?
My first search on Ebay for the sensor board shows they are available for under $5.
All the code etc is here...
 
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