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Old 13-Aug-2020, 11:10 PM   #1
Junior Member
Join Date: Aug 2020
Location: Rockport, Maine
Posts: 7
Understanding dB & Amplifiers

Thanks for the opportunity to request a bit of schooling.

The attached screenshot is from the best screen I ever owned, a 60" plasma by Panasonic. (it's gorgeous) The feed comes from a TiVo Roamio OTA Series 5. (Perhaps later we can discuss their use of % as a unit of measure.)

I'm located in Rockport, Maine, 40+ miles from RF Channels 2, 7, 9, & 13 in Bangor. The antenna is the VHF section, only, of a ChannelMaster 3020 with their new version 3 of the CM7777 preamp. I'd like to add something like the variable gain SKY38323 distribution amp ahead of the TiVo. Specs say it can add 25dB to VHF signals.

Signal levels, expressed as a %, vary from day-to-day, hour-to-hour, from a low of 37% to a high of 60% and better. Of course, SNR tracks that, predictably. Most days, most channels are virtually free of dropouts. There are 4 ATSC tuners in the TiVo. Even for quite low signals, the TiVo reports Signal Lock, Program Lock, and Search Complete to be "Yes."

The caution I often hear is, "No amplifier can create signal. The pre-amp can take what is at the antenna and "Boost" it in order to help with the signal loss over the down lead coax cable coming in to the house."

My question:

IF the distribution amp can increase signal level between its input and output sufficient to overcome the signal loss about to be added by X-teen feet of cable before a splitter and cable headed off to a couple of mythical destination receivers with ATSC tuners,

THEN isn't that increased RF level available and in play, regardless of whether the destination is 100 feet away or 1 foot away, and we're hitting a 4-way splitter before ATSC tuners in the TiVo box?

In other words, wouldn't the Channel 2 RF signal level be increased by some net amount, measurable with the proper gear, and register as both a Signal Level and SNR improvement on the TiVo? My assumption has been that both the preamp and the amp add signal and noise, but each adds far less noise, for a net gain. Is that my mistake?

Or is it the fact that we're no longer living in an analog world that's driving the difference? Is digital reality somehow that much different from my analog recollections?

Be assured, I like learning stuff even when it contradicts what I think I know. : )

Thank you
Attached Images
File Type: jpg TiVoScreenshot-Smalljpg.jpg (200.6 KB, 504 views)

Last edited by rsw1941; 13-Aug-2020 at 11:13 PM.
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