Friday, May 13, 2016

Rolling Up the Radials

May is the end of 80 meter season. At least it is for me now that the weather has warmed and the grass is growing. Growing grass means mowing the lawn, an activity not entirely compatible with on-the-surface radials. According to my plan when I turned my ground-isolated tower into an 80 meter antenna the radials had to be removed in the spring. I'm not the only city dwelling ham following this seasonal ritual.

However I've not actually done that. The radials seem so settled into the turf that I experimented by doing the first mowing of the season with the radials in place. There was no hint of a problem. You can see in the picture how I stapled the radials at the tower base to keep them as low as possible. Wood made this easy. Their ends are secured with long nails, as pictured in the antenna article (link above).

I left the title of this article unchanged since I chose it before deciding not to remove the radials. Perhaps I'll leave the radials where they are for the time being with the hope of working a few stations on 80 during the upcoming CQ WPX CW contest.

Despite aborting the rolling up of the radials let's pretend that I did just that and that my 80 meter season is over. It mostly is finished in any case now that summer QRN has arrived, as have new man-made QRN sources that came with a couple of new neighbours and an LED lighting system included in one neighbour's renovation project. It's now a very attractive kitchen but those lights may explain the new QRN coming from the north. It is not only the low bands that are affected.


This is a good opportunity to look back on the winter low-band season that was. The low bands aren't easy for me with the strong local QRN on 80 and the impossibility of a highly efficient antenna on 80 and 160. Although I didn't have high expectations I did set objectives that seemed realistic at the time. In my judgment these modest objectives were largely met.

The highlights of my season on 80 include:
Not all went so well. There were also many disappointments:
  • I did not reach DXCC. My count is 88 worked and 68 confirmed on LoTW. Although the antenna does not work all that well I very well could have made it to 100 if not for the QRN. This blight severely limited DX opportunities and QSOs during contests. As the saying goes: you can't work them if you can't hear them. Using a 40 meter inverted vee for receive helped a little, though not nearly enough.
  • I expected better on 160 with this antenna. My worked count was below 20, and only 1 station worked in Europe (who answered my CQ!). Those 8 meter long radials are vastly inadequate.
What I do next on 80 will depend on my circumstances. If I keep this QTH I will improve the antenna. If I move I would like to build the parasitic array design from a previous article. A big question mark remains hovering over this dilemma.

Limits of modelling

NEC2, and even NEC4, do not accurately model near-field ground losses of ground-mounted vertical antennas. Many have noted this in both amateur and professional ranks. It's a fundamentally challenging problem. Experiments have often shown higher losses than those predicted.

Knowing this fact means that I can only try to further minimize ground loss by improvements in the radial system. This will not be easy. As a first step I will backtrack from my modelling adventures of last year and instead use fewer but longer radials: 4 x 20 meters. Since the available surface is 14 meters wide it is impossible to lay down a symmetric pattern of radials that long. Instead I'll take the 4 radials, start them out with a 90 separation and then run them along the property lines.

This is not ideal, for several reasons. First, 4 radials is inadequate. What I hope, based on my literature research, is that more of the return currents will be picked up with this arrangement, despite what NEC predicts. At least the longer radials should greatly improve 160 meter efficiency, even more than on 80.

Second, with a small number of radials it is difficult to equalize radial currents. Ground structure varies a lot, even over a short distance, and the ground depth on 80 and 160 is many meters. Unequal currents can reduce radial field effectiveness and make tuning of the vertical less predictable. That latter is easily remedied in the L-network.

Third, asymmetry and bending of the radials may reduce effectiveness. Based on what I've read on the subject this may be the least of my concerns. However it will limit my ability to increase the radial count with either short radials or long, straight ones since current inequality will be unavoidable. The short radials need not even be considered since they'll not carry any significant current in this arrangement.

It comes down to choosing the lesser evil. That's all I can hope to do unless and until I move.

Solar influences

Looking forward, the low bands will become increasingly important. Cycle 24 is forecast to end in 2020, with Cycle 25 beginning perhaps one year earlier. For the next 4 to 5 years the low bands -- 40, 80 and 160 meters -- are the places to be. Efficient, low angle radiators and directive, low noise receiving antennas are mandatory for DX and contest success.

If I don't move the prospects for amateur radio for the next several years are not promising. I don't want to be in that position. In setting priorities for my next station the low bands will loom large. Big antennas for 10 meters can wait a few years.

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