SNR and Signal Strength from antenna, what do these numbers mean? - AVS Forum
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post #1 of 3 Old 11-21-2007, 09:23 AM - Thread Starter
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Just bought a 32" LCD Toshiba and have been looking at the Signal Strength menu numbers. I'm getting SNR (signal to noise ratio?) of 27.0 to 33.7 on 7 channels received, and signal power of 36.3 - 47.9. What do these numbers mean? There seems to be no relationship between SNR and Signal Strength - a low SNR can have a high Signal Power rating. I'm very impressed as the analog stations on an old Hitachi CRT came in rather snowy at times, but on this new TV I always get a great HDTV picture.

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post #2 of 3 Old 11-21-2007, 09:47 AM
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Quote:
Originally Posted by John Frank View Post

I'm getting SNR (signal to noise ratio?) of 27.0 to 33.7 on 7 channels received, and signal power of 36.3 - 47.9. What do these numbers mean?

Hm, without units I'm not sure what the "signal power" value means, but SNR (yes, signal-to-noise ratio) is expressed in dB, representing the differential between the signal level and the noise floor. 27-34 dB is an excellent SNR range - with OTA digital, you want to generally have at least 26 dB. However, I've got a local station that broadcasts on VHF channel 2 for ATSC digital, and even with an ~26 dB SNR, I get uncorrectable errors like crazy - I think that's just a side-effect of using low VHF. :/ The rest are in UHF frequency space, and tend to do far better.

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There seems to be no relationship between SNR and Signal Strength - a low SNR can have a high Signal Power rating.

Yes, that's correct - though an extremely low signal strength will generally not yield good SNR, overall SNR is more important, as if the SNR is too low, the signal can't be reasonably differentiated from the noise, causing errors in extracting the signal data.

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I'm very impressed as the analog stations on an old Hitachi CRT came in rather snowy at times, but on this new TV I always get a great HDTV picture.

Yes, and my OTA NTSC locals look pretty lousy too, even with my TiVo Series3 HD, but the ATSC locals (other than the aforementioned low-VHF broadcaster) come out quite clean. It's just the nature of the transmission method, it seems - though the trouble is, it's great until you reach the proverbial edge, at which point you'll get either MPEG garbage or nothing at all.
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post #3 of 3 Old 11-21-2007, 03:58 PM - Thread Starter
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Thanks man. It's all UHF and your post makes me quite happy with the results.

Have a great Tday!
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