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what are ideal power levels and snr
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Old 24-04-2012, 09:05   #16
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Re: what are ideal power levels and snr

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Originally Posted by General Maximus View Post
you need a reboot to fix the power on that 5th channel
will do when I get home, that did suprise me one of the channels being very high, any reason for that.
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Old 24-04-2012, 09:12   #17
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Re: what are ideal power levels and snr

It's a firmware fault, it's not really that high
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Old 25-04-2012, 08:18   #18
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Re: what are ideal power levels and snr

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Originally Posted by General Maximus View Post
you need a reboot to fix the power on that 5th channel
just rebooted it now and all looks good

Downstream Channels
Lock Status Modulation Channel ID Max Raw Bit Rate Frequency Power SNR Docsis/EuroDocsis locked
Locked QAM256 58 55616000 Kbits/sec 307000000 Hz -1.6 dBmV 38.6 dB Hybrid
Locked QAM256 56 55616000 Kbits/sec 291000000 Hz -1.0 dBmV 39.4 dB Hybrid
Locked QAM256 57 55616000 Kbits/sec 299000000 Hz -1.5 dBmV 39.5 dB Hybrid
Locked QAM256 59 55616000 Kbits/sec 315000000 Hz -2.0 dBmV 39.4 dB Hybrid
Locked QAM256 60 55616000 Kbits/sec 323000000 Hz -0.9 dBmV 39.9 dB Hybrid
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Old 25-04-2012, 08:56   #19
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Re: what are ideal power levels and snr

cool
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Old 25-04-2012, 09:58   #20
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Re: what are ideal power levels and snr

My power levels are all around 20dBmV and my connection worked fine when it was 4 channels. Now it is 8 channels it keeps cutting out and I'm not sure if it is because of maintenance work for double speed, or if the signal being that high has caused problems now the channels have increased.

Looks like I am going to have to give faults a call.
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Old 25-04-2012, 12:18   #21
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Re: what are ideal power levels and snr

If you now have 20 dBmv downstream and you have 8 channels, under the 3 dBmv doubling rule (you'll have to Google that), the aggregate power hitting the modem is 29 dBmv which is close to the 33 dBmv DOCSIS 3 limit. Domestic cable modems are cheap items and in any case the DOCSIS 3 spec says that no single channel should exceed +17 dBmv. So tuner crosstalk, overdriven amplifiers and so on are failure conditions that you are experiencing.

My advice is that you either et a VM engineer to attenuate your modem input by 20 dB, or you go on eBay and buy two 10 dB forward path attenuators (85 - 860 MHz sensitivity); fit them in series on the end of your coax cable and all that will be sorted.
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Old 25-04-2012, 12:34   #22
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Re: what are ideal power levels and snr

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As per Mon General's post. Stick it on if power rises to 11 dBmv or higher and let us know. That level is unhealthy because when you have 8 downstream channels, that would hit the DOCSIS 3 input maximum for a cable modem.
Nah, 8 channels = 2^3, so total power = 11 + 3 + 3 + 3 = 20dBmV, very short of the maximum 33dBmV.

Each doubling of channels increases total power by 3dBmV on the logarithmic scale, so even if the power were perfectly balanced to break 33dBmV with an average power of 11dBmV you'd be looking at bonding 256 channels, 256 channels at 11dBmV average giving 11 + (3 x 8) = 35dBmV, the 3 x 8 is due to 256 being 2^8.

Across 8 channels you actually need an average power of 24dBmV per channel, a tad outside the specifications.

EDIT: Which is what you said in the post before this one, I'm guessing you had an off moment on the post I quoted there
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Old 25-04-2012, 12:46   #23
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Re: what are ideal power levels and snr

Yeah - I realised that when answering the other post you referred to.

Thanks.
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Old 25-04-2012, 14:02   #24
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Re: what are ideal power levels and snr

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Originally Posted by Sephiroth View Post
My advice is that you either et a VM engineer to attenuate your modem input by 20 dB, or you go on eBay and buy two 10 dB forward path attenuators (85 - 860 MHz sensitivity); fit them in series on the end of your coax cable and all that will be sorted.
Thanks, I will try calling faults. Hopefully they will see the problem straight away and send someone out, rather than make me jump through several hoops first. Otherwise I will try ordering some attenuators.
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