I live less than 7 miles from the towers, and only own one TV, so it doesn't much apply to me, but I was wondering...What's the difference, electrically and functionally, between a mast mounted preamp, the amp inside a distribution block, and the little 9v power inserter sold with "amplified" rabbit ears?
Preamp vs Distro Amp?
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In general the mast mounted preamp will have lower noise figure and greater gain. A distribution amp will have more noise, less gain but more "power". The distribution amp won't overload so quickly. The amp in the rabbit ears is maybe an amp chip that has very limited operating parameters. The rabbit ears are not going to overload it. They will be noisy. The noise figure is how much extra noise the amplifier introduces to the signal as it amplifies it.
If you are a long ways from the towers, a pre-amp is required for the amplification as close to the antenna as possible, as the signal is extremely weak. Without a pre-amp, by the time the signal traveled down 100ft of coax, there would be very little or no signal left to amplify.
So are you saying that if you're in an outlying area, say 50-70 miles from all signals, the preamp and distribution amplifier are to be used in series?
With analog audio signals, I know that double-amping causes problems because the "big" amp takes all of the noise, distortion, and clipping that the first amp creates and makes it louder/worse. Is this as big of a problem with digital TV signals?
Yes, to answer your last question first.
Did you mean distribution amp when you said "Distro"?
If you are in a marginal reception area, the mast-mounted preamp will give you the best opportunity to have a usable signal at the set end. You probably won't need a distribution amp at all unless you're splitting that signal to several locations. Your best bet would be to first try no amplification to one set and work your way "up" from there. If you have a marginal signal then the preamp would be your next experiment. Get a low noise, quality unit as others mentioned. Once you have a usable signal at one set then you can experiment with splitting to additional locations and let that tell you if you need a distribution amp or not. If you do add one, get a low gain unit (or a variable unit set to low gain) and thus use only enough amplification to offset the split. E.g., a 2-way split means (ideally) a 3dB loss to each set, so a distribution amp with just 3dB gain per tap (or perhaps a bit more to cover the other minor losses of splitting) would probably be best. In the case of amplication more is definitely not better unless you are in an almost hopeless fringe situation, like I am. Noise is in part an artifact of amplification, so more gain = more noise, and noise is the bane of digital signals!
50-70 miles is really pushing it for UHF signals especially (which tend to be more line of sight vs. following the earth's contour as VHF signals do to a greater extent) unless you are either very high up or in flatlands with almost no obstructions...
Did you mean distribution amp when you said "Distro"?
If you are in a marginal reception area, the mast-mounted preamp will give you the best opportunity to have a usable signal at the set end. You probably won't need a distribution amp at all unless you're splitting that signal to several locations. Your best bet would be to first try no amplification to one set and work your way "up" from there. If you have a marginal signal then the preamp would be your next experiment. Get a low noise, quality unit as others mentioned. Once you have a usable signal at one set then you can experiment with splitting to additional locations and let that tell you if you need a distribution amp or not. If you do add one, get a low gain unit (or a variable unit set to low gain) and thus use only enough amplification to offset the split. E.g., a 2-way split means (ideally) a 3dB loss to each set, so a distribution amp with just 3dB gain per tap (or perhaps a bit more to cover the other minor losses of splitting) would probably be best. In the case of amplication more is definitely not better unless you are in an almost hopeless fringe situation, like I am. Noise is in part an artifact of amplification, so more gain = more noise, and noise is the bane of digital signals!
50-70 miles is really pushing it for UHF signals especially (which tend to be more line of sight vs. following the earth's contour as VHF signals do to a greater extent) unless you are either very high up or in flatlands with almost no obstructions...
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