Golborne Vintage Radio

Loops are interesting and predate long wire aerials (clue in name) and earth. But the very long waves and then long wave (still called Medium Wave in 1928, and MW was called Short Wave then), meant loops went out of favour except for portable receivers (replaced by ferrite rods in the 1950s).

The snags with a loop for transmission is the remote tuning and very high voltage at any significant power, and thus motorised vacuum capacitors.

An end fed half wave monopole also has matching and voltage issues. A 100W is about 700V at the matched base and thus 10kW is about 7,000V.

I did have a big length of heliax style feed found discarded at a mountain top mast that I considered using to build a loop. The inner core is hollow copper like micro bore. The idea would have been to split a big gap on the outer, earthed at the two bottom ends and then the inner would be an unbroken loop. It would have been about 2m diameter. The issue was mounting, suitable vacuum capacitor and remote operation of it. You need to measure at the feed point. So I gave it away to someone with motorised vacuum caps, though he has never built it either.

Embassies tend to have very large HF log periodic aerials on the roof. I saw an amazing one on the US embassy in either Prague or Brataslava.

Hi Michael.
Vacuum caps are horrendously expensive, I think that in itself puts people off. Although I can use 50 watts I am a hardened QRPer, in fact the 80meter band loop tuning capacitor flashes over above 15-20 watts, I've a wider spaced and better quality one that I'll fit hopefully when I rebuild it with copper pipe rather than stranded wire, rigidity is important as loose wires cause drift of SWR if they move. I'll be making the tuning cap motorised as well.