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Message: [QUOTE="Piggie, post: 20060, member: 2941"]I agree with Jeff Hartman's Rule 5 given the constraints he stated. 1) Noise level is a fixed quantity of the type of components and design of the amp.  2) Radio Shack made some 2 stage TV amps.  They had a preamp on the mast powered by an indoor box inside that was not only a power supply but a small 10 db or so amp with a gain control.  This is exactly I think what Jeff eludes to in no point in adjusting the gain on the inside amp in no way affects overload on the top amp.3) Rule one of anything, fewer parts means less failures. Any technician of any kind, from automotive to electronics knows that cold.==========I should have added to make my point clear is adjustable gain at the initial mast head amp (despite the more parts to fail theory) is not into itself a bad idea, and could be adjusted to reduce overload.  But noise figure is the deal killer in this amp. 5db is way too high.  3 db is acceptable these days for DTV.  For those that can't relate to the difference between 3 and 5 db, well it's 2 db, but what is 2db to someone that isn't used to thinking db?Here is a good example of db in the real world.Lets say you have the biggest antenna you can buy, but want more signal, so you stack two of them together to increase reception.  The resulting advantage of two identical antennas over one is 2.5 db though a common combiner. Or lets say own an antenna with a 60 inch long boom.  To get 2 db more, you would need to buy an antenna with a boom 2/3's longer or 100 inches.So if you save $10 bucks on a cheap amp, and have a 100 inch boom antenna on the roof, you just reduced the antenna to one that would have reception of one that is only 60 inches.High noise amps are absolutely a no no for DTV. There is no point in buying one.That said, if you already own an older high noise amp, it may work ok for you if you have strong signals, and need the gain of the amp to over come long runs of coax. This does beg an idea or though to you Don. Take a CM7777, it already has 2 switches on it. One for combined or separate and one to add or remove the FM trap filter.I wonder if it would not be a good idea, since a switch is more reliable than a pot to add a switch to something of the gain and low noise of a CM7777 that drops the gain in half, if and only if that drop also gives an increase in the dynamic range of the amplifier. The reason I add that last constraint is if you look at holl_and's evaluations of amps, even though the CM7778 has 10 db or so less gain than the CM7777, it apparently has no better dynamic range.So I will add to Jeff's rules, that without an increase in dynamic range, there is no point in lowering the gain of an amplifier.[/QUOTE]

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