Two, or four?

I'm continuing with side-by-side experiments using different numbers of radials on elevated 1/4 wave verticals.

Ready for deployment. The feedpoint is at 1.5m when installed.

 

Last evening, I set up two identical antennas for 14MHz, one with four radials, the other with only two. My previous post compared two radials with only one. The experiment ran between 17:06 and 18:24UT, so it's a snapshot comparison for the moment.

For this work, I created a plate that slips over the fibreglass pole and is a big improvement over trying to mount things 'dangling down' from the pole, which makes for a lop-sided feed point and radial tension is not so easy to equalise. This proved to work very well indeed, though I need to make a better, final version to tidy things up a bit.

Now, before I go on to the results, it's an idea to reflect on Les Moxon's problem, discussed in his excellent book HF Antennas for all locations when he depicted a four-radial vertical and asked, in relation to coupling of the radials with the the coax feedline: 'how does one achieve symmetry?'  He was thinking at the time about low-to-ground feedpoints, the problem being lessened by raising the feedpoint (as I do by default), burying the coax, or shortening the radials. 

Moxon's 'problem' of additional imbalance due to the feedline.

 

In my case, I simply run the coax vertically down immediately from the feedpoint and is of the same length as the feedpoint is above ground. With WSPRlite transmitters, this is great; with real transceivers, not so much. The elevated feedpoint sorts this problem out in that situation, more or less.

Back to the experiment. Everything identical, except no plate for the two-radial antenna (direct connection to an SO239). 200mW out, both antennas on the same moist, rich ground with an entirely open landscape all the way around. Matching was 1.12:1 for the 2-radial antenna, 1.15:1 for the 4-radial version.

This was the coverage, pretty-much identical for both antennas:

200mW goes far.

A simple table (click to expand) shows more efficiently the outcome, rather than plotting graphs and so on. Overall, we get a small advantage for the four-radial antenna, though for several US east coast receivers, the advantage was much more significant - up to +7dB. Also, the four radial antenna is typically heard more often, although there are exceptions. 

A longer test is necessary, but it's a good first indication. The elevation pattern seems much the same, based on more local stations' reports, but that the overall efficiency is somewhat improved.

I've done these tests inland rather than at my usual coastal haunts. Not many people have easy access to the coast, and the ground there is so near perfect at RF that the number of radials is much less important than over soil; often, a simple copper tube in the ground is more than adequate (and much safer, in public areas). 

For portable coastal work, the difference is likely to be much lower or none at all. Over normal ground that most people operate from, it's too much hassle to deploy four radials, at least to my mind. But for permanent installations, especially if the ground conditions are not very good (arid zones, etc) the additional effort of installing more and perhaps many more radials is certainly worthwhile.