Wire Length for 20m Delta Loops

An update on the delta loop is overdue.  I love these antennas.  They turned amateur radio from a noisy, poor signal sort of hobby into one where I could enjoy global DX for essentially no cost.

I've had my moans about how difficult it is to find reliable information on getting a delta to resonance, and I still don't understand why so many different views, because deltas are not especially sensitive to their environment.

Sometimes, you just have to use one of these.  Just not too much!

Anyhow, I decided to go out and do a proper job of getting my delta to sing properly today.  No wind, and a warmish winter day helped.  I disconnected the coax, attached an SWR meter to my old TS-50 running on a car battery, and then hooked up with a short piece of coax to the 4:1.  The whole set-up, radio and all, remember, was outside, working at the antenna itself, with no more than about 1.5m of coax in the connections.

As it was, I knew the antenna was too long.  This was because I stupidly tried, being a bit green behind the ears a year ago, to tune the antenna using the ATU.  This is a very dumb idea for two reasons: meters on ATUs seem not to be so good on cheaper models, and measuring the SWR at the transceiver, rather than antenna end makes the SWR look better than it is because of losses in the coax.

So, a year wiser, I sent a signal into the delta.  The meter read 3:1 at the upper end of 20m, 2.5:1 at the lower end: the loop was, as I knew, too long.  Although it's obvious what I had to do next, you always have that feeling that, when you chop wire, at some point, you'll end up regretting it.  Antennas don't play ball and slowly drop to a good SWR like they're meant to.  They often stop at some value well short of 1:1, and then start climbing.

After a good old chop that brought me back to a piece of tape on the wire I'd marked the theoretically-correct length a year ago - 21.3m - I found the SWR was beginning to bottom-out at 1.6 to 1.7:1.  That's good enough for me, and I expect it would not go much lower, if any with further chops, especially as the 4:1 balun almost certainly brings the system impedance down below 50 Ohms.

Coming back indoors, I found the match at the transceiver end almost perfect, needing no ATU to work 20m and with a near-full 100W going out.

Job done.  I hope!