The need for change
My 20m Delta Loop had been in place since April 2019 when the lunchtime net moved from 15 to 20m and had the point fixed about 37 feet up in one of the large Oak trees at the top of my garden.
Since then the Oak trees have grown and new branches and a multitude of leaves and twigs covered up the antenna changing its impedance when wet and pulling the wires out of place.
After some thought I decided to dismantle the triangular Delta Loop and install a single 20m square Quad Loop further away from the Oak trees putting the antenna in the clear yet still facing towards the east coast of the States.
Recycling and renewing
I already had one aluminium mast which supported one end of my 80m Doublet so I strung a new (blue) polyprop rope from this and utilised the original halyard and pulley which had supported the point of the Delta Loop for the other end. This gave me a horizontal rope at 37 feet on which to hang my new antenna.
I then made up a square loop from 2.5 mm stranded plastic covered copper wire (blue) with 17 foot 9 inch sides fitting thimbles at three corners with one bottom corner connected to the 450Ω feedline via a commercial junction piece. The above lengths are the result of my calculations to construct an antenna which would resonate at 14.345Mhz. I pegged out the loop on the lawn with tent pegs to form an accurate square and cut 73 feet of wire from the roll to make up the 20m loop which actually measures 71 feet around.
I then fitted two 20 foot lengths of cord to the thimbles on the bottom two corners to prevent the square Quad loop from moving about and hoisted it all into the air.
The result is that I now have a vertically polarised square Quad Loop (with no front to back ratio) with the top wire at 37 feet and the bottom about 19 feet off the ground. This faces Bob, N4XAT and David, WB1EAD and puts an S9+30db signal into Barry, SA7GDB (his report to me yesterday). David WB1EAD was still able to read my SSB signal when I turned the output of my FTDX 3000 down to 5 watts output. Bob was also able to work me on CW from his home using his MFJ magnetic Loop even when I reduced power so that satisfied me that the new loop is working well.
Because I choose to feed this loop with 450Ω line rather than coax I am also able to match (but not resonate) the loop and feedline for a 1:1 match on 21, 18, and 7 Mhz giving 4 HF bands from a single length of wire, and you could do this too.
I fitted a commercial 1KW 1:1 Current Balun at the shack end of the 188 feet of 450Ω line I need to reach the loop and the balun connects to my manual ATU via 6 feet of mini 8. I don’t worry about needing 188 feet of feedline since 450Ω line has a loss of only 0.15db per 100 feet at these frequencies. Compare that with the coax feeder you are using.
Why 450Ω Ladder Line?
You could make up one of these square loops and feed it with coax but in this case you’d need to fit an electrical quarter wave matching stub made from 75Ω coax between the loop and your 50Ω coax but then you’d only have a single frequency loop since that set up would not match on other bands.
There you are, something to think about. The wire and ropes used don’t have to be blue but as I’ve said many times before, It’s all about antennas!
73, Ken G3WYN.