What kind of s/n ratio do I need to get a lock?

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Marcus Aurelius
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What kind of s/n ratio do I need to get a lock?

Post by Marcus Aurelius » Sat Dec 16, 2017 4:14 pm

Hello all! I hope you can indulge a noob with his first post. I have wrestled my way though a MythTV install and setup on Ubuntu 16.04 LTS (kernel 4.10) and I think I'm very close to getting this thing to work. I'm using a Hauppauge winTV quad tuner card (PCIe) and it works in KaffeineTV. I can pull several stations with my indoor quad-bowtie antenna.

However, scanning for channels in MythTV is not going so well. I have increased the signal and tuning timeouts to 30000. After many tries, I got three channels detected. Going to the frontend and selecting "Watch TV", I get a screen and some errors. Near the bottom, I see "Signal 83%" , "S/N 2.3 db", and "partial lock". My guess is signal is too weak.

My question: What is a typical S/N with an indoor antenna and a transmitter within 30 miles or so? What is a minimum S/N for myth to permit viewing? My next step is to mount the antenna in the attic and add an inline amplifier. I'm beginning to question my selection of a quad-tuner card. Undoubtedly, the signal is being split between the four with a resulting loss.

Glad to have found this forum! Thanks in advance for your help!

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Re: What kind of s/n ratio do I need to get a lock?

Post by wesnewell » Sun Dec 17, 2017 5:30 am

Got a good outside antenna (CM 4228) about 40 miles from the transmission towers and get 85% at 2.5 db. I've got this feeding 9 tuners (3 dual pc tuners, and 3 other tuners) , but had to have a distribution amp in the attic once I got over 4 tuners iirc. On last scan with a new tv, I got 114 channels and one old analog channels. My antenna is about 20-30' from the 2 way distribution amp which splits the 2 outputs to 2 feeder cables to the tuners. I'm still using mythbuntu 14.04 and mythtv 0.27.
Backend-GF8200A, AMD Phenom II B95, 6 atsc tuners. Frontends-GF8200's,,AMD Athlon II's. Mythtv user since 2005.

Marcus Aurelius
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Re: What kind of s/n ratio do I need to get a lock?

Post by Marcus Aurelius » Mon Dec 18, 2017 3:23 pm

Thanks for your reply! I guess I'm close. I know the signal is marginal because it sometimes "breaks up" or drops audio with my current antenna and running KaffeineTV. I'm going to relocate it to the attic and add an inline amplifier. Hopefully that will give Myth enough to work with.

Marcus Aurelius
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Re: What kind of s/n ratio do I need to get a lock?

Post by Marcus Aurelius » Sat Jan 13, 2018 3:00 pm

Okay, so that wasn't the problem. I've got the antenna in the attic and an inline amp. When I plug the antenna directly into the tv all the stations come in crystal clear. Connected to Myth, nothing changes. Still no lock, timed out, no channnels found. I thought I was close because on one instance, it found the strongest of my local channels and identified them, but when I go to the frontend and try to watch, it times out. FWIW, I've got the timeouts set to like 20000, so that's not the problem.

Since my initial post, I've re-installed the OS and I'm now running 16.04 with kernel 4.4. No improvement. I'm ready to try one more time with 17.04 Zesty. What else can I try? The device comes up with lspci -v, looks okay. I have the required firmware. Don't know what else to try. Halp! :-)

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Re: What kind of s/n ratio do I need to get a lock?

Post by pvr4me » Sat Jan 13, 2018 3:53 pm

Are you using the exact same cable and moving between the TV and tuner? Cables can really matter to RF signals. One stray strand of braided insulation can ground out all the signal.

Also, most TVs have more robust circuitry to deal with over and under strength signal levels. I would eliminate the amp, and focus on a single channel to start--the one with the best signal according to TV Fool (or similar). If you can get it working, then scan for the others.

Post a link to your TV Fool report and maybe we can give more specific advice.

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Marcus Aurelius
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Re: What kind of s/n ratio do I need to get a lock?

Post by Marcus Aurelius » Sat Jan 13, 2018 7:38 pm

Thanks for your reply!
I have a good bit of confidence in my signal, but I'm very much in doubt of the tuner card being properly addressed by the OS. I've been digging through dmesg, and it alerts me to the fact that I am using an experimental version of the media stack, something about an old kernel (4.4) and yadda yadda. I am going to reinstall the OS, choosing this time to go with Zesty. Third time's the charm???

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