Originally Posted by keenan
Based on the above referenced notes, could one assume that the Winegard AP-8275 pre-amp is the best available..? Or, would the CM-7775 be just as good because of the lower noise number? Put, simply, what is the highest performance pre-amp available?
BTW, thanks to all who have contributed in this thread, there is a wealth of info here, I'll admit that some of it is beyond me, but a great resource nevertheless.
That would depend on what your definition of 'highest performance' was.
Most of the Winegard amplifiers have the same maximum output level before signal clipping occurs. (Clipping is very bad because it will absolutely kill DTV signal while it just makes NTSC horrible to watch.) So the difference in gain between the various Winegard pre-amps is how much input signal the pre-amp can handle before clipping at the output occurs.
So if you lived in a town in the middle of nowhere, where all of the NTSC channels were very snowy, maybe the AP8275 or the more popular AP8780 would be just your cup of tea. On the other hand, if you lived fairly close to the transmitter and were using the pre-amp to overcome the losses of your attic (antenna in the attic scenario), the lower gain AP8700 would be a more appropriate pre-amp.
Another thing that is often overlooked when comparing different brands of amplifiers is how many channels the gain is actually specified for. At UHF, the Winegard specified gain is for 5 TV channels, while Channel Master uses just 2 channels to specify its gain. In Houston we have 32 channels on the air and the pre-amp sees all of them, wether we watch them or not, wether they are analog or digital. Consequently, in Houston, the higher gain pre-amps overload even sooner than the manufacturers specs would have you belive. Also, keep in mind that it only takes one channel to cause the clipping. Just one extra strong channel can cause a pre-amp to wipe out all of the rest of the channels for you.
For the most part, a couple of tenths a dB difference in Noise Figure (NF) can be ignored. (And again, you have to know the manufacturers method of determining it before you can start splitting dBs.) However, the difference between a 7 dB and a 3 dB NF is significant. Pre-amps tend to have a 3 dB or less NF while line amps (distribution amps) tend to be up in the 5, 6, or 7 dB NF range. I know there are folks that will disagree with me on this one but the truth is, if you live inside of 60 miles from the transmitter and the NF is less than 3 dB, don't kill yourself trying to get a lower number.
You'll find the Channel Master 7777 a very popular pre-amplifier on this forum. It performs well in the field and in many different locations and situations. It doesn't overload 'too' easily. The VHF and UHF inputs can be split for combining two antennas. The CM7775 has one flaw in that it will not pass VHF like a Winegard AP4700 will. If your area has a broadcaster that is going to go back to VHF after the NTSC kill date, then the 7775 is going to present a problem for you.
The Winegard pre-amps are less popular here but not necessarily because of any performance issues. The Winegard amps are often harder to find locally, while the CM7777 seems to be available everywhere and can be easily taken back to the store for a refund. Someday, I'll get a hold of an AP8780 and test it against my CM7777, then I would be willing to say which one has the 'highest performance'.