With some unavoidable chores out of the way I finally went further on my quest to erect a better antenna for 20 meters. The question asked last time on why the rooftop vertical performed below par was solved pretty quickly: the ground connection to the coax lead had come loose and after I fixed that it performed better, but still not as well as the garden vertical (the garden vertical about 10 dB better than the rooftop vertical).
VK3DZ made an interesting remark in the comments on my last article: “keep VHF antennas at least 12 meters high to avoid short-range noise.” My antenna is for HF, but the more distance from noise sources the better and maybe more distance from the metal roof would also help. So I got my fiberglass poles out and put the garden vertical up on the roof, 4 meters above the metal roof.
A good comparison could be made with the other vertical, but the difference was minimal: signals strengths were comparable and noise levels were the same. After a couple of days I put the garden vertical back in the garden and put my delta loop for 6 meters on the roof.
In a private e-mail exchange a while back Steve (VE7SL) wondered if tying the ground connection directly to the metal roof would have an effect. The question was related to long- and medium wave reception, however it would be a good experiment to see if it would have an effect on my rooftop vertical. Up till now my ground connection has been a single 90 cm ground rod, which did a good job of syphoning off some noise. When I bought that rod my local hardware store said that the longest one they had was 90 centimeters (3 foot), but when I went out to buy some more there recently they gave me 180 centimeter ones (6 foot). I got two for about US$15, so well within my budget. I connected them with twin solid core electrical copper wire and after an hour of pounding on them in 35 degree heat (Celsius, not Fahrenheit) they were in.On medium- and longwave the difference was huge: a 10+ dB gain across those two bands. On 20 meters it didn’t matter at all, but it was a nice experiment and at least I have a better ground system now.
Unfortunately we had a typhoon coming through and it damaged the garden vertical. After fixing it I will have to make plans for the next antenna experiment.