Is there a way to calculate the real SNR from the snq percentage?

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Nounours
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Joined: Thu Sep 12, 2019 3:22 pm

Is there a way to calculate the real SNR from the snq percentage?

Post by Nounours » Thu Sep 12, 2019 3:45 pm

Hello,

I'm using hdhomerun_config on a HDHR5-4US unit to get the "snq" (Signal Quality), and I would like to convert the percentage value I get back into an SNR in dB. I've searched the internet and couldn't find how to do this anywhere. I did see on some old documentation that hdhomerun_config used to report it (example: "snq=90 (29dB)"), but not anymore.

I would also be interested to know if there's a similar way to translate the "seq" (Symbol Quality) percentage back into its basic definition of "number of uncorrectable digital errors detected". What does that percentage effectively mean? Does seq=100% mean no correction were necessary? How about 50% or 0%?

Thank you in advance.

jasonl
Silicondust
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Joined: Sun Oct 28, 2007 9:23 pm

Re: Is there a way to calculate the real SNR from the snq percentage?

Post by jasonl » Thu Sep 12, 2019 6:08 pm

For ATSC, 100% SNQ is 30dB+, 50% is 16dB.
SEQ is a logarithmic scale of packets with errors in the last second, 50%=9, 0%=99+

Nounours
Posts: 6
Joined: Thu Sep 12, 2019 3:22 pm

Re: Is there a way to calculate the real SNR from the snq percentage?

Post by Nounours » Fri Sep 13, 2019 9:44 am

Thank you for the quick response Jason. Much appreciated!

Another quick question if you don't mind: when getting /tuner0/debug on a HDHR5 device, I get something like this:
tun: ch=auto:33 lock=8vsb:587000000 ss=99 snq=85 seq=100 dbg=-3500/373

I gathered through some research online that the first number of the "dbg" parameter is related to Signal Strength (seems to go down and up linearly). Am I correct? What about the second number?

nickk
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Re: Is there a way to calculate the real SNR from the snq percentage?

Post by nickk » Fri Sep 13, 2019 10:50 am

The dbg value is model dependent... there could be 2 or 3 numbers depending on the model and the meaning varies by model.

The last number is the one that could be interesting - it is the carrier offset in Hz.

The lock frequency also corrects for offset but at 125kHz resolution.

If you deliberately tune 125kHz off frequency you should see both the last dbg number and the lock frequency reflect the correction needed.

Note that the dbg number is not officially documented and could change with new models and/or firmware.

Nick

Nounours
Posts: 6
Joined: Thu Sep 12, 2019 3:22 pm

Re: Is there a way to calculate the real SNR from the snq percentage?

Post by Nounours » Mon Sep 16, 2019 8:23 am

Thank you for the information Nick. Much appreciated!

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