Qam16/qpsk - Page 2

pip08456 · 09-05-2011, 18:05

QPSK is not necessarily crap. It is an only indication of an upstream noise problem, the modulation has been automatically adjusted to take account of this.

It does not mitigate any other problem on your area of the network, eg over utilisation etc.

Ignitionnet · 09-05-2011, 18:30

Quote:

Originally Posted by Efour

Would this explain why my PL is shocking for the past 3 days
im also on the QPSK crap now

20 mbit at POPLAR ubr London..

Its unplayable peak hours

Yes that could well be it, chops the available bandwidth in half.

chambohambo · 11-05-2011, 12:04

Checked modem today and noticed the downstream has dropped from 7.5 DBMV what would cause this to happen? and I am still on QPSK upstream.

Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 168
Downstream Frequency : 323000000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 0.9 dBmV
Downstream SNR : 37.0 dB

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 35800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 5120 Ksym/sec
Upstream transmit Power Level : 49.7 dBmV
Upstream Mini-Slot Size : 4

craigj2k12 · 11-05-2011, 12:31

Quote:

Originally Posted by chambohambo

Checked modem today and noticed the downstream has dropped from 7.5 DBMV what would cause this to happen? and I am still on QPSK upstream.

Cable Modem Downstream
Downstream Lock : Locked
Downstream Channel Id : 168
Downstream Frequency : 323000000 Hz
Downstream Modulation : QAM256
Downstream Symbol Rate : 6952 Ksym/sec
Downstream Interleave Depth : taps12Increment17
Downstream Receive Power Level : 0.9 dBmV
Downstream SNR : 37.0 dB

Cable Modem Upstream
Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 35800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 5120 Ksym/sec
Upstream transmit Power Level : 49.7 dBmV
Upstream Mini-Slot Size : 4

they will be making changes at the network end, which could possible affect your power levels, however your levels awere out of spec before, and are now well in

chambohambo · 11-05-2011, 13:05

Oh I thought power levels and stuff was all to do with the green cabinet. So do you mean at the UBR?

pip08456 · 11-05-2011, 13:21

Quote:

Originally Posted by chambohambo

Oh I thought power levels and stuff was all to do with the green cabinet. So do you mean at the UBR?

It's a little more complex than that as a problem could be at the cabinet or the UBR or anywhere inbetween.

A read of this may assist you to understand better.

chambohambo · 11-05-2011, 14:15

Is it normal for the downstream power level and snr to be bouncing around slightly? just noticed when I keep clicking refresh but then when I keep hitting refresh on upstream power level it just stays stuck on what it is.

pip08456 · 11-05-2011, 14:38

Yes as long as it is not massive jumps.

chambohambo · 11-05-2011, 15:29

How come the upstream doesn't bounce around but downstream does?

Nedkelly · 11-05-2011, 16:01

The downstream can be affected by heat in the main cabs with amps .In the summer you can loose 3db and in the winter gain 3 db .what also could be happening is that the network has been reset due to the maitanence that is going on .Here we visit every cab with a amp in once a year and check all forward and reverse levels 1000+ cabs done every year its like painting the forth rail bridge once you finish you start again .

Ignitionnet · 11-05-2011, 18:38

Quote:

Originally Posted by chambohambo

How come the upstream doesn't bounce around but downstream does?

Upstream is a transmit power and only changes when the power arriving at the other end goes outside a certain range, it is only adjusted when needed. What you're seeing on the downstream is the receiving power at your modem.

Peter_ · 12-05-2011, 09:17

Quote:

Originally Posted by craigj2k11

they will be making changes at the network end, which could possible affect your power levels, however your levels awere out of spec before, and are now well in

Actually both sets of power levels are well within spec.

craigj2k12 · 12-05-2011, 13:04

Quote:

Originally Posted by Masque

Actually both sets of power levels are well within spec.

i said they were out, look at post 15 (they were slightly high)

Peter_ · 12-05-2011, 13:39

Quote:

Originally Posted by craigj2k11

i said they were out, look at post 15 (they were slightly high)

I did say both sets of power levels and neither are over 11.

pip08456 · 12-05-2011, 15:30

I wouldn't be happy if downstream was over 7dBmv. But that's just me.