Sunday, February 10, 2019

The single element HF wire vertical delta loop

Only got a single high support? Don't have quite enough room for a dipole? After a loop style of antenna with a reputation for low noise reception? Or want something that can easily be changed from vertical to horizontal polarisation?

If so then the single element delta loop could be your saviour. It's a simple antenna to build comprising a wire approximately one wavelength perimeter. Feed it at the bottom centre for horizontal polarisation or down the side for vertical.  If you've got two supports you can have it pointing to ground (with a higher average height) or if you only have one you can have the apex pointing up.  The latter is particularly convenient for portable operating where you can use a telescoping fishing pole mast to hold it up.  It doesn't matter very much if it's not quite an equilateral triangle.

A single element delta loop doesn't have a lot of gain. Possibly a shade over a half wave dipole. But in its vertically polarised version it can give good low angle radiation, particularly if near salt water.

A challenge with the delta loop is how to feed it.  That's because its impedance is quite a bit higher than 50 ohms. It's not quite like a ground plane (about 35 ohms, but higher if you droop the radials) or a half wave dipole (about 70 ohms, but lower if you make it an inverted-vee). Options include using a matching section (a quarter wavelength of 75 ohm coax multiplied by its velocity factor), some sort of transformer or open wire feed with a balanced antenna coupler.  Open wire feed will allow the loop to work on multiple bands down to about 70% of the design frequency. The links below will give some good ideas on feeding this antenna.

40 - 10 m delta loop Comprehensive article by GU3WHN (PDF)
Multiband mono delta loop by DU1ANV (PDF)
$10 No transmission line delta loop Eham article by KE7WAV
Vertical delta loop Elmer Hour beginner guide from the Villages Amateur Radio Club (PDF)
Amongst the Kilowatts Part 1 I describe and demonstrate a 14 MHz portable delta loop (video)
Amongst the Kilowatts Part 2 More on my 14 MHz portable delta loop (video)

Start reading, start watching then start building. They're so cheap that you could even make several.

PS: Looking for even more things you can do with amateur radio? 99 things you can do with Amateur Radio can help. Available in both electronic and paperback.

1 comment:

  1. I feed mine (for 11m) with a 2:1 balun. I use it on the country side stationary on a special bracket attached to my SUV with a 10 meters telescopic pole. I have found that it is quiet and super broad banded and works better than a dipole. 2AT111


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