Info and Questions on my situation:
TVFool reports that all the stations I am interested in are in exactly the same location, 20 miles away, and signal strengths at my location range from -48 to -70 dB. All UHF, line of sight (I am on a hill and the transmitter is on a mountain)
I have two TV's: One upstairs and one in a half-basement. A MANT510 work barely adequately on some stations in the in the basement, and was actually fairly decent when located upstairs, but with occasional digital artifacts and drop-outs. If I ran the MANT510 signal into the pre-wired cable-TV lines from upstairs to downstairs, the downstairs TV would get better, but still not perfect. The ridiclous amount of amplified gain of the MANT510 would only help when upped to maybe 10 dB max.
So I figure I needed just a little stronger antenna signal, with minimal gain and low noise.
So I bought a radio Shack 15-2160 and mounted it in my attic (thin layer asphalt shingles)http://www.radioshack.com/product/in...entPage=family
The Performance of this antenna was a slight improvement over the MANT510 on the upstairs TV, but was worthless when it had been split off to go downstairs also (through the cabnle TV line. All other branches of the cable tv line were disconnected)
So, I got a CM 7777 and mounted it close to the antenna. This actually degraded the picture upstairs, evidenced by more noise and digital drop-outs, and didn't help the downstairs much.
Question: What signal level is considered "too high" ? I know that -100 dB is considered the lowest level for reasonable reception, but I don't know where "too much" is. Imagine my signal strength is -49 dB, I get another +12 dBd from the antenna, and +26 dB from the preamp, with a -4 dB loss at the splitter, giving me about -15 dB at the upstairs TV.
Thinking I might be overloading the upstairs TV, I moved the CM7777 to a position AFTER the splitter, so the Antenna signal is unamplified through the splitter, and only the leg going to the downstairs gets the amplification.
THIS SEEMS TO BE WORKING WELL. I imagine there might be only 40-75 feet of coax between upstairs and downstairs. So I speculate that I was overloading the upstairs TV, and the +26 dB of the amp is not overloading the downstairs because of the losses of 40-75 feet of coax.
Is this making sense ? I am surprised that the reception is so sensitive to signal level such that +26 dB overloads the upstairs but is necessary for the downstairs. It makes me think there s only a range of acceptable signals that is about the same as the loss in the coax which mught be only 8 to 12 dB (a rough estimate).
Is this true ?
Thanks for any insights.