I knew I was going to spend some time in Italy so, for the occasion, I decided to design another QRO loop to be installed permanently over there. I’m calling it the IZ6 Loop.
This time I decided to use a smaller capacitor so I selected a Comet CVLI-125CC/8 which does 5-125pF and peaks at 8kV (I got it from Ebay for $149).
The reason for a smaller capacitor is I realized that going above 150pF is generally counterproductive: on the low bands performance isn’t going to be good and – at the same time – the extended tunable range will require micro-stepping and/or gear reductions. The low bands demand a separate, multi-turn (or larger) magnetic loop which would still require less than 150pF.
This particular capacitor doesn’t come with a pre-made shaft so I had to draw one. First I printed it in plastic then I decided to have it manufactured in aluminum for an extra $10.
The enclosure I used is of the same kind I used on my other loop, but a bit smaller in size. I’m still using N connectors for the radiator disconnects and ethernet for the control wires. The stepper motor is a simple 38mm NEMA 17. Because of the small capacitor size, no micro-stepping nor gears are needed. I also tried using a 23mm stepper but that size would work unreliably due to lack of adequate torque.
I have designed a simple support to hold the capacitor and the stepper in axis. The support can be printed on most 3D printers and on a large variery of materials without supports.
The exciter loop is made using the quick and dirty splitter I recycled from my last project. This part could be better but, hey, I have a much larger family now (and a lot less time).
Radiator is made with 10ft of LMR600 coaxial cable and resonates between 7.4 to around 30 MHz (a 8 or 9 ft length could easily cover 40 meters as well but given the poor performance it would have I am not interested in cutting it).
The rest are standard bolts, washers and nuts. Add a cheap controller, some spare time, a lot of patience and there you go: for less than $300 you have a fully featured, vacation ready QRO magnetic loop.
Results are quite good. So much so that I am planning to install it permanently on the roof, probably with a rotor.
These are the main parts I used:
- Capacitor Comet CVLI-125CC/8 ($149)
- Stepper Motor NEMA 17 38mm ($6)
- Enclosure QILIPSU UL94-V0 Outdoor Electrical Box 8.3″x6.3″x3.9″ ($26)
- Pole Mount QILIPSU Pole Mounting Kits, 304 Stainless 175x48mm ($14)
- Ethernet connector PENGLIN 2PCS RJ45 Panel Mount Screw Terminal Adapter ($10)
- Capacitor/Stepper Support and Loop Splitter (printed in house +$10 for metal shaft)
- Loop Controller (EA7VHO or K1FM)