Wednesday, December 7, 2016

Building a Delta Loop for 20 Meters

So far within my new paddock  I have installed my top band antenna, (which seems to work very well). However, I'm getting itchy feet to try another antenna. The one I've always wanted to try is a Delta Loop antenna, specifically for 20 meters.

The one advantage I have here is that my take off points around the house are pretty good especially towards Australia and opposite towards the Americas. I'm fairly high up at about 700 feet above sea level with no major obstacles apart from the odd tree dotted around the garden and they say from the Cotswolds east towards Russia the next high ground you hit are the Urals which are well over a thousand miles away, so you can see my take off points are pretty exceptional.

Reading the reports about the Delta Loop, they are a quiet on receive and with vertically polarized loops good on low angle radiation so I reckon they would work well around here for some serious dxing. I thought about which band I would set it up for and came to the decision of 20 meters simple because there would be a high amount of activity both in the Americas and Australia so I should have no problem with contacts especially in the part of the low activity cycle.

I'd like to use Plan D with the apex at the corner, to maximise a good low angle of take off. I have a spare 30 foot telescopic mast which I can lengthen a further 10 feet should I require it and tying off the bottom corners should not be a problem

Calculations for the antenna are fairly simple, to determine the length of wire needed for the desired band you simply divide the resonant frequency in Mhz into 1005 and because the impedance is normally 90 to 120 Ohms you can either use a quarter wave length of 75 ohm coax to match or a 4:1 balun (which I will be using). You need to have a triangular shape (or near as) for it to work properly and of course an ATU will be required. Better to cut slightly longer and use a good SWR analyser to tune the wire to your desired frequency.

I've had to order some more wire , but so far that's been the only expense. So hopefully this will work out as a fairly cheap project. More updates to follow!

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