Is s/n better higher or lower?

For discussion related to MythTV which doesn't belong in another forum.

Moderator: Forum Moderators

Post Reply
wmorrison
Junior
Posts: 59
Joined: Sat Dec 01, 2018 12:05 am
United States of America

Is s/n better higher or lower?

Post by wmorrison » Fri Oct 11, 2019 10:29 pm

I've been searching and can't find where this is documented. I'm talking about the message that pops up when you begin watching a channel, that says:

Signal nn% | S/N n.ndB | BE n

I know it's signal to noise ratio, but is higher or lower better? What numbers are considered marginal, good, best?

Where is a webpage describing this? Googling the actual text on the screen hasn't found anything for me.

blm-ubunet
Senior
Posts: 101
Joined: Sun Jun 15, 2014 1:08 am
Cambodia

Re: Is s/n better higher or lower?

Post by blm-ubunet » Fri Oct 11, 2019 11:49 pm

Higher is better within reason.
Too high can be a problem because it could cause gain compression. I don't think that's a big problem with DVB broadcasting or modern RF frontends.
Using cheap nasty RF amplifiers & broadcast FM interference can be a problem.
As long as the BER bit error rate is low/zero you are fine. After that more signal makes no improvement.

I recall in the past the S/N values were not directly comparable between diff drivers/tuner cards.

~$man femon
femon -H

Need to (t)zap the tuner first or just let MythTV tune the card.

wmorrison
Junior
Posts: 59
Joined: Sat Dec 01, 2018 12:05 am
United States of America

Re: Is s/n better higher or lower?

Post by wmorrison » Sat Oct 12, 2019 12:15 am

blm-ubunet wrote:
Fri Oct 11, 2019 11:49 pm
I recall in the past the S/N values were not directly comparable between diff drivers/tuner cards.
That's what I've just been reading, that there's no one standard for the numbers reported by the drivers.

Mine's a Hauppauge WinTV QuadHD. S/N is always shown as about 2.5dB, for all channels, but BE is usually 0 and picture is fine.

femon shows completely different numbers than MythTV, but I guess I'm fine and the drivers are funny.

blm-ubunet
Senior
Posts: 101
Joined: Sun Jun 15, 2014 1:08 am
Cambodia

Re: Is s/n better higher or lower?

Post by blm-ubunet » Sat Oct 12, 2019 4:12 am

Same tuner card here except the DVB-T/T2 version.
femon does not seem to work on my system any more.
I'm using dvb-tools V5 API ppa so could blind scan/tune DVB-T2 test broadcast sometime back.
"femon" mode in this tool:
dvb-fe-tool -m
signal -48dBm C/N > 36dB
4.7dB indicated in mythtv
19Km line of sight with maybe 25% of total dispersion blocked by hills.

Post Reply