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Old 21-Aug-2015, 12:45 AM   #20
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,569
Quote:
I removed the Kitztech KT200 pre-amp, and reinstalled my CM7777 preamp
Which 7777 do you have, the old one with separate inputs for VHF and UHF, or the new 7777 with one antenna input?
Quote:
I see very little difference in the signal levels on my Tivo between the two pre-amps.
Are you talking about signal strength or SNR on the TiVo? Often signal quality as defined by SNR and errors is more important than signal strength with digital signals.
Quote:
Does anybody know (for SURE) what the CM7777 pre-amp is for db and noise level? I think around 2db noise, but not sure on the signal level.
The old 7777 had a listed vhf gain of 23 dB and a noise figure of 2.8 dB; 28 dB gain and 2 dB noise figure for UHF. The new 7777 is 30 dB gain and "ultra low noise" noise figure, whatever that is. When the new version came out, they said NF ≤ 5 dB; now they don't say anything about NF.

Many of us techs were really upset with PCT when they bought out CM, closed the NC plant, and fired first grade RF engineers. But what really got us was when they redesigned the 7777, but kept the SAME model number to seemingly trade on the good reputation of the original 7777. This bothered many of us, so that we stopped experimenting with the CM preamps, stopped recommending them, and started recommending other brands. Then Winegard started shrinking and cheapening their preamp line. Then Antennacraft folded. We are left with CM, Antennas Direct, and RCA. Antennas Direct dropped their excellent CPA 19 and replaced it with the Juice, which is in short supply. There is also, as you are aware, a selection of very low noise preamps, but they have a history of sensitivity to static damage.

To answer your original question, the old 7777 figures are accurate according to my crude measurements. The new 7777 is an unknown.

Calaveras, of AVS, uses a Tin Lee 30 dB UHF MA-25U-77 preamp for his two 91XGs that he likes very much.

http://www.tinlee.com/MATV_headend.p...#AntennaPreamp
http://www.tinlee.com/MATV_headend.p...#AntennaPreamp
http://www.tinlee.com/PDF/MA-series-info.pdf

Quote:
Does anybody know of an available UHF/VHF preamp that has a higher level JUST for VHF?
More gain for VHF?
I agree with No static at all.
You don't need more gain for VHF, you need to put the antenna where the signal is.
Quote:
I don't think the VHF antenna quite clears the roof of the house I have to aim over for vhf channel 12.
First it was the trees, and now a house?

After looking at your tvfool report, I think a simple folded dipole antenna above the trees and house would be good enough for 12.
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Last edited by rabbit73; 21-Aug-2015 at 1:22 AM.
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