RF can do funny things. I have often found that the strongest signal is with the aerial pointing slightly off from the direct line of sight to the transmitter. The difference can be as much as 2 or 3 dB.
If you look around at the aerials in your location you'll probably see them pointing in slightly different directions. If we presume that at least half the aerials near where you live were installed by competent tradesmen using professional meters then you'd expect half the aerials to be pointing in the same direction if direct line of sight gave the strongest signal level.
3dB is double the signal level, or equivalent to the power loss of the signal travelling down 20m of decent coax (WF100), so not a small difference at all. Amateur meters - the £10-£20 jobs sold online or in the likes of Maplin/Screwfix - are hopelessly insensitive; they just don't have the resolution to detect a 3dB change accurately. The signal level detection in most TVs is wildly optimistic too, so they're no good for this kind of fine tuning either. Coming back to meters then, by the time you have spent enough to get a meter with decent resolution just on signal power alone to do the final alignment it's the same cost as hiring a pro installer. His meter will also give the Signal to Noise ratio and should be capable of doing a slope test to see the relative levels from all the muxes rather than just the aggregate level. It'll get you a better result.
I'm all for people getting some knowledge and having a crack at some of their own work. There does come a point though where DIY is counter-productive and paying a pro is the better solution.
If you look around at the aerials in your location you'll probably see them pointing in slightly different directions. If we presume that at least half the aerials near where you live were installed by competent tradesmen using professional meters then you'd expect half the aerials to be pointing in the same direction if direct line of sight gave the strongest signal level.
3dB is double the signal level, or equivalent to the power loss of the signal travelling down 20m of decent coax (WF100), so not a small difference at all. Amateur meters - the £10-£20 jobs sold online or in the likes of Maplin/Screwfix - are hopelessly insensitive; they just don't have the resolution to detect a 3dB change accurately. The signal level detection in most TVs is wildly optimistic too, so they're no good for this kind of fine tuning either. Coming back to meters then, by the time you have spent enough to get a meter with decent resolution just on signal power alone to do the final alignment it's the same cost as hiring a pro installer. His meter will also give the Signal to Noise ratio and should be capable of doing a slope test to see the relative levels from all the muxes rather than just the aggregate level. It'll get you a better result.
I'm all for people getting some knowledge and having a crack at some of their own work. There does come a point though where DIY is counter-productive and paying a pro is the better solution.
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