40m Delta Loop - Going Flatter

As the autumn bares its teeth, it's that time of year again when evenings will see 20m close, and reliance put on 40m for night-time operations.

Last winter, I threw up a half loop for 40m, fed against ground (radials would, of course, be less lossy!)  It received very well indeed, and had very low noise.  But it wasn't all that good on transmit.

So, time for something else.  I've never found horizontal antennas work very well from this site.  Time to put up another delta loop.  At 42-43m round trip, that's a big loop!

43m of wire held up by a rather flimsy 8.5m of fishing pole (centre).  A tall tree is much better!  At right is the 20m loop, which has put up with five years of Atlantic winds by now.  That open horizon makes for good radio!

Luckily, there is no need for perfection when it comes to loops, with flattened ones - up to a point - even exhibiting a slight increase in gain over an equilateral one.

So, I gathered various bits of wire and soldered them to form a 43m-long loop.  I worked out that, with a standard 10m fishing pole, using 8.5m due to the weakness of the upper sections, I could, on a less than windy day, get about 10-12m of sloping wire either side of the apex up in the air, with 18-20m forming a very long base wire!  It connects at one corner, for mechanical simplicity, to a 4:1 balun.  If I had any spare, I would have used twin wire to a balun outside the shack as the losses are much lower than in coax.

It works!  I've run a standard quarter wave vertical against the delta on WSPR, which allows semi-objective testing, and within the limits of propagation variability, they perform identically, putting out the best or very close second best (within 1-3dB) signal to DX stations on 40m from the UK (or indeed anywhere else across the EU!)  The best signal on the test evening, incidentally, was another welsh station running a 160m doublet up at 16m - itself quite a beast!

No well-intentioned '599' here.  My flattened delta is usually in the top two strongest signals to LA9JO from anywhere in Europe.

A loop this big is ungainly and gets in the way of normal garden use. It also needs a relatively large - or at least a long garden. But if you can squeeze it in, it's ideal for 40m nighttime use during winter and can be matched-up for use on higher bands.  At 20m, the first harmonic, you could be looking at 7dBi gain at 20-30 degrees departure angle, taking you into 3 element yagi performance territory or beyond for the price of some wire.  It won't, however, be the best antenna for local NVIS contacts, for which a low-hanging dipole will obviously be much better.

 For very windy days, a much sturdier non-conductive support will be needed, or a tree.  Sadly, trees will be a little hard to come by in my garden for the next 20 years or so, so I will look yet again at buying a pole or two from DX-Wire.