In my last blog post, I was concerned that my FM antennas were raised too high for the mast. The antennas themselves, bother Triax FM5s, were attached to the rotator via a 6 feet (almost two metre) tall mast. This was surely going to place too much strain on the rotator bearings.
The weather was calm and so I thought I would leave the antennas for a few days so I could see if there was any significant difference in reception. The overall height above the ground was now close to 30 feet or 9 metres with this new height.
Also worth noting was my experience with the exceptional Dutch tropo I had on June 23rd - when both antennas were lying on the ground for maintenance!! This really made me wonder if my antennas had been too far above the ground all along.
The spell of calm weather did not last long. The winds increased quite suddenly on the morning of July 2nd. I was not expecting this. I looked at the FM mast and saw that it was leaning quite markedly into the neighbouring park. It was immediately clear that this mast was not going to survive these strong winds, which were forecast to continue for the rest of the day. I rushed to get the mast down as quickly as possible, narrowly avoiding a park-bound catastrophe. Phew!
Two days later (yesterday) and the mast was back up, but I had replaced the 6 foot top section with a much shorter, foot long stub. I cleaned up the antenna connections once again, checking reception before hoisting the mast back into the air, only to find that the vertical FM5 had stopped working once it was back in place. Annoying! So I will have to get the mast down yet again to fix this. Luckily, I have some replacement bit and pieces from older FM5s.
So what did I make of reception with the antennas higher and then lower? This is actually quite interesting.
With the antenna some four feet higher, the FM5 directivity was *very* noticeably improved. I can't say that the gain was any better. Perhaps by a tiny amount, but not enough to sing and dance about. Noise levels were reduced by a few dB though. My main desktop computer used to cause severe QRN to my reception, but this was no longer the case.
With the antenna lowered by about six feet, noise levels from my desktop computer had increased considerably. I recently made a few changes to my FM DX setup, now doing all my FM DXing on a noiseless laptop. The only real noise now is from the solar panels on the roof which, though not particularly bad, add an additional 2 or 3 dB to the general background noise, regstering around 4-6dBf on the TEF receiver. I can live with this. Medium wave, on the other hand, is totally obliterated. Luckily, my medium wave DXing is done at the farm, some 10km to south of here. Directivity still seems reasonable with the mast lower, but I noticed that general FM scatter has improved by several dB. Wow! The biggest improvement has been to the south, with national French TDF transmitters from sites like Hirson, Amiens, Brest, rouen, Rennes, Le Mans, plus others and even as far south as Strasbourg and Bourges.
So it's now down to lowering the mast once again to fix the vertical FM5, during which time I will lower the antennas by a further two feet. I will add an update to this article if there are any obvious improvements in reception.
Concluding, it does seem that my DX reception was reduced by having the mast higher. Why would this be? Something to do with ground reflection? I have no idea. Maybe somebody would like to comment.
