Originally Posted by bobchase
I don't know about the Mulberry tree. In Houston the pine trees were the signal killer while deciduous trees were fairly light on the attenuation. Going ten feet higher, like trying a pre-amp, is an experiment in time, energy, and money.
Sorry I can't be more definitive for you.
Bob is correct. Actually, very correct. I agree that CM makes the best preamps, too, because they seem to have a lower noise figure than others, which essentially means when others get marginal, the CM may still be able to pull certain distant channels in. But "distant" usually refers to 35-40 miles and over. IOW, if you are closer than that, it may not help at all, and might even aggravate the situation.
In analog reception signal power was the goal, because as the ratio of signal power to the noise floor got lower, the picture got noisier. You needed 43-46 dB above the noise floor to get good PQ, so the focus was on getting the most RF signal you could get. With digital, it is a complete paradigm shift. Signal power is much less important, because in some instances (not OTA TV) data can be extracted perfectly even if below noise. You need only a minimum of 15 dB above noise (but in practical applications I recommend 20 so you don't get annoying tiling every so often when atmospheric issues play with that level).
For digital, the game is more the ratio of signal to multipath interference. Not having line-of-sight reception means high multipath. That makes sense. 8VSB was adapted specifically because it does not have interference capability into adjacent markets; instead of coherent interfering signals, the curvature of the earth means that 8VSB bleeding into an adjacent market presents more as a slight increase in the noise floor, and all of that was particularly important when digital and analog needed a 10-year crossover period and both were out there competing with each other in an RF sense.
Newer tuners can also equalize out multipath reflections remarkably better than they could even a few years ago (so newer TVs get better reception in marginal areas), but the name of the game is still to minimize the interference as much as possible, and that is the focus rather than sheer RF power. Raising an antenna, even if it does not give you line of sight, can only help, but not because it will give you more signal (unless you gain line of sight by doing this); it will, but it also improves multipath because reflective surfaces are now further away (you are now above them more) and the angles of reflection are also more in favor of reducing the interference. How much it will help is anybody's guess based on a lot of local issues, but generally, higher is better.
The other effective way to do this is by getting the most directionality you can get. High directionality maximizes the front beam and minimizes off-axis reflections, which again, maximizes the ratio between them. It has the side benefit of more gain, as well. I like the CM 4228 for those reasons, it is the least-expensive and most-compact antenna among the top-shelf highly-directional antennae out there. I also recommend an FM filter, which removes about 17 high-power carriers coming at you from S. Mt, which can only help. I get about 5 ticks higher on my signal quality readings when I use an FM filter.
At 18 miles with a rooftop antenna, I would predict that a preamp will not help, because first of all there is already plenty of signal power, most likely, and a preamp will raise the level of RF power right along with raising the multipath interference level (which is usually the issue) meaning that it does nothing to reduce the ratio between the two, and so has a net zero effect on reception, even if it raises signal levels by 15-25 dB. Preamps are mostly a legacy fix for distant analog reception issues.
Trees are not helpful, but at the frequencies we are talking about they usually do not cause much attenuation. Trees that have needles may be worse. OTA does not get rain fade like DBS does, either. But obviously, the water molecules in the leaves can act like tiny antennae and absorb some of the RF like tuning forks, or it can smear the arrive time which makes decoding that much harder.
What it comes down to is how much risk you want to take. The only way to find our whether better reception is possible is to make these sorts of incremental improvements one by one until you either get there, or don't. Bottom line, there are tools; there are techniques, and all of them will make some small or hopefully larger improvement. But all of them together in a bad reception area will sometimes not be enough to move the needle, and by then you have spent a couple hundee and are sort of stuck with whatever you end up with. So it comes down to your level of motivation.Edited by TomCat - 2/3/14 at 10:29pm