“So I am a big fan of Kevin Loughin’s YT channel and also of Mag Loops having already bought an unwanted YouLoop on Facebook Market Place. Watching this video Ham Radio - Magnetic loop transmitting antenna overview and details inspired me to aquire some parts. The first issue for a Mag Loop is TX power, the YouLoop is rated for 250mW, not going to get me far, the secret to a good Mag Loop is a variable capacitor form an old valve radio. This will handle the sort of voltages involved upto maybe 25w. I am QRP at 5w so not big deal. Sure enough a silent-key (amateur operator who has died) son was advertising some assorted parts, one box contained a couple of air dielectric capacitors. I set off my my motorbike into deepest Staffordshire last Autumn and acquired them. One has a slight misalignment causing shorts (which I have since fixed), but the other was fine. I measured them with my multimeter and they are 100pf close each gang. This means I can set them to 50pf, 100pf or 200f depending on whether I use 1 or 2 gangs in series or in parallel.
I built a prototype using an Arduino Uno, but I wanted to have soldered connections, so I rebuilt in on a prototype board specifically designed for Arduino Nano (wider spacings in the centre) and installed a Arduino Nano Every that I had spare.
Supplies:
- An Arduino Uno or Nano
- Stepper motor with ULN2003 driver pcb
- A motor coupling
- Air dielectric variable capacitor from a valve radio
- RG23 cable 5m
- RG58 a few metres
- multiple PL259 to fit both cables
- multiple SO 239 sockets
- a project box”