Pyramid Loop Antenna (20m version)

As summer slowly relents to autumn here in the UK, it's time to get low-height, efficient antennas going before the onslaught of hurricane winds begins.

Recently, I wrote about my WSPR tests of a half lambda DDRR antenna.  This got to most parts other antennas were reaching, but usually much more weakly.  It did manage to get into Wake Island in the Pacific on 5W output, although the actual radiated output was probably much less.

It was time to put that experiment to bed for a while, and recycle the wire into a full 20m loop (which works out at 21.3m in this case!)  But, to keep the height low, and because I had always been interested in the antenna, I decided to fold the antenna on itself, creating what is usually called a 'pyramid' loop.  This is what it looks like (don't heed the dimensions for 20m, they are for another band):

Easy peasy!  Seems to be a good performer, too.  It's easily scaled, without taking a whole field, to cover 40m (6m per side) or 80m bands (12m per side).

I took an old, broken 7m fishing pole and used only the first 4m sections.  These are quite thick, so hardy in the face of fierce gales.  It's cable-tied to a stout fence post, giving it plenty of support.  300 Ohm twin is cable tied to the top, and the two ends of the loop attached to a twin-feed dipole centre.  The loop is then pulled out with stakes and light rope.  For DX performance, keep the two triangles reasonably vertical; a flattened-out pyramid will give a higher peak radiation angle.

WSPR tests shows this antenna performs really well.  It's too early to give meaningful numerical comparisons, but on its first evening of operation on 20m, it's achieving very much the same signal strength at DU1MGA as other UK stations, so it's obviously not a bad antenna in any sense.  What's more, with each 'leg' only 3.5m long, it easily fits in a very modest garden of the sort often found across the UK.

I haven't determined the precise radiation pattern as yet, but a quick near-field assessment with an RF meter seems to show nice, strong vertically-polarised radiation from the front and back, and horizontally-polarised, possibly mixed polarisation from the sides.  I'm useless at modelling, so will have to rely on others to do so.