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Old 14-Aug-2020, 3:15 AM   #2
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,738
Quote:
Originally Posted by rsw1941 View Post
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.

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?
Hello, rsw1941; welcome to the forum.

An amp will make the the channel 2 signal stronger, but it will also amplify the ambient noise at your location, resulting in no improvement in the SNR.

Here is a sample signal report from rabbitears.info showing very poor signals at the intersection of Ship St and Pascal Ave in Rockport:
https://www.rabbitears.info/searchma...tudy_id=135056

You can do your own report for your location here:
https://www.rabbitears.info/searchmap.php

It is true that a preamp usually has a lower internal noise figure than a tuner, but on VHF the noise levels are higher than on UHF. This means that the noise figures become irrelevant because they are buried in the much higher local noise. The NFs of the amp and tuner are stated as noise above the reference level of the Thermal Noise Floor at about -106 dBm for a digital TV signal with a bandwidth of 6 MHz.





The TiVo signal strength is just a relative scale; 40% is very low. An SNR of 16 dB is just barely enough. Uncorrected errors should be zero; 111728 is way too many. Corrected errors are never shown, for some unknown reason.



VHF-Low is even worse at my location:





Channel 3 must be extremely strong to have enough SNR above the very high noise level.



The SNR is measured from the noise level to the top of the signal.



So, to answer your question, more amplification is not likely to solve your reception problem for channel 2, but you are welcome to try it. It will not improve the signal quality (as defined by SNR and errors) coming from the antenna. It will be necessary to improve the signal quality coming from the antenna terminals before any amplification.

The CM3020 is quite large in order to receive VHF-Low channels. There aren't many antennas with more gain for channel 2 than the 3020. Review of the 3020 by Tyler the Antenna Man:

https://www.youtube.com/watch?v=jpjcO8PUC88

You will have to find a possible location for your antenna that has more signal strength for channel 2 and less noise for an improved SNR.



The WLBZ terrain profile from the sample report shows a very difficult signal path with your location behind a hill:

Attached Images
File Type: jpg rsw1941tvfTiVoScreenshot_1.jpg (131.9 KB, 982 views)
File Type: jpg rsw1941TVFp3WLBZ.jpg (109.0 KB, 936 views)
File Type: jpg rsw1941reportREestimated2.jpg (245.2 KB, 991 views)
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Last edited by rabbit73; 14-Aug-2020 at 6:18 PM.
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