So I finally got round to doing the maths and making a loop for 10m. A bit of Pythagoras and a bit of trig and I had some lengths. I used 1005/F(mhz) to get the length of the loop in feet. Then multiply by 12 and 2.54 to get it into sensible units. This version has an apex at the top and is fed part way up one side. Full dimensions to follow.
It needs a 1/4 wave transformer made from 75ohm coax to get the match to 50ohms. I had some 3m lengths of quality satellite coax with N and F connectors so out with the MFJ259b to measure the Vf for the cable, about 0.8. 1/4wave of 75 ohm cut for 28.3MHz and the whole kit and caboodle thrown up in the garden. I connected up a 50ohm feeder to the 1/4transformer and had a tune on the MFJ to see how bad it was.
The design was for 28.3MHz (mid way between CW and SSB sections) and this is what was measured.
Top useable frequency with SWR 1.4
Bottom useable frequency with SWR 1.4
That will do for a first pass. SWR is a bit high for 10FM so I’ll look into that later.
I’ve built loads of antennas but they’ve always needed a bit of fettling, I’ve never hit the design point 1st time before. 