Power levels & attenuators

tim · 24-03-2005, 17:29

I used the info here http://homepage.ntlworld.com/robin....ips/signal.html to do some checking.

This is what I got:

Code:

Frequency 	 402750000 Hz Locked
Signal to Noise Ratio 	31 dB
QAM 	64
Network Access Control Object 	ON
Power Level 	-15 dBmV

Upstream 	Value
Channel ID 	1
Frequency 	33584000 Hz Ranged
Ranging Service ID 	1573
Symbol Rate 	2.560 Msym/s
Power Level 	44 dBmV

Software Version: SB4100-4.0.6-SCM-NOSHELL
Hardware Version: 0
MIB Version: II
GUI Version: 1.0
VxWorks Version: 5.3

The downstream power level seems on the low side.
I then remembered that there a 2 attenuators between the cable feed and my SACM (SB4100).
They are 3DB and 10DB. I removed them both to see what the results would be.

This what I got:

Code:

Frequency 	 402750000 Hz Locked
Signal to Noise Ratio 	35 dB
QAM 	64
Network Access Control Object 	ON
Power Level 	-3 dBmV

Upstream 	Value
Channel ID 	1
Frequency 	33584000 Hz Ranged
Ranging Service ID 	1573
Symbol Rate 	2.560 Msym/s
Power Level 	29 dBmV

I just need to check with the knowledgable here whether I have done the right thing.

Thanks

tim · 27-03-2005, 13:24

68 reads and no comments

Any takers?

BTW I'm in the Baldock SG7 area.

**Paul** · 27-03-2005, 13:50

It's easter - people are away.

Ignition · 27-03-2005, 14:12

Quote:

Originally Posted by tim

I just need to check with the knowledgable here whether I have done the right thing.

Thanks

*nods*

Before:

Signal to Noise Ratio 31 dB
QAM 64
Network Access Control Object ON
Power Level -15 dBmV

After:

Signal to Noise Ratio 35 dB
QAM 64
Network Access Control Object ON
Power Level -3 dBmV

More SNR is good, power level of 0 is optimal, -15 is on the outside of the specs for receiving a service.

tim · 27-03-2005, 14:33

Thanks.

Just wanted to check.

Hmmm, wonder why the attenuators were there in the first place?

Ignition · 27-03-2005, 15:08

You were probably on a higher powered 'tap' in your street cabinet meaning that power coming into your modem was much higher than it is now and have been changed to a more appropriately powered one for the distance you are from the cabinet.

Keep an eye on it though nonetheless, incase something untoward has happened to cause the power going into your modem to drop, and once that's fixed you'll be way overpowering modem.

Ta.

greencreeper · 27-03-2005, 15:26

Not wanting to hijack the thread but Ignition makes an interesting point. So am I right in reading that you can have a perfectly working modem for ages, and then a house a few doors down has broadband fitted, or NTL alter the setup/configuration, and your service degrades? Do the engineers know this and would rather be reactive and wait for customers to report faults? My green box is almost on the wall of my house. I keep seeing engineers in the box and it worries me. I feel strangely protective towards it. Should we all be doing what Tim has done, say every month, in case something has changed?

tim · 27-03-2005, 18:56

Quote:

I keep seeing engineers in the box and it worries me

Yup same here.

Quote:

I feel strangely protective towards it.

YES, so do I

(no net = withdrawal symptoms)

There are a LOT more houses with Cable Modems now than a few years back when I got mine.
In fact, I think I was the first person on my local 'Green box' to get one.
All the additions must have diminished the power to my cable feed.

Ignition · 27-03-2005, 19:33

Quote:

Originally Posted by tim

Yup same here.

YES, so do I

(no net = withdrawal symptoms)

There are a LOT more houses with Cable Modems now than a few years back when I got mine.
In fact, I think I was the first person on my local 'Green box' to get one.
All the additions must have diminished the power to my cable feed.

Nah, that's assuming they didn't have TV from ntl in the first place which would have had the same effect.

Additions dropping power like that isn't going to happen, the power is split evenly between a series of taps and those taps that aren't used have insulators on them to absorb the RF, so power loss is the same however many subscribers are attached.

2||Para · 28-03-2005, 15:44

Spoke to BB support again today [is there call centre in India?] and they told me Cambridge area isnt ready for 3mb service!! Which is wierd as i get 3mb speeds every now and then.Then of course it drops completly and i have to reboot the modem.BB Support at its usual tricks it seems,dont know the answer and cant fix the problem,make up any crap and put the phone down!