Cable Forum - Superhub Downstream channel ID 'slope' ?

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- - Superhub : Downstream channel ID 'slope' ? (https://www.cableforum.uk/board/showthread.php?t=33702095)

SnoopZ

02-01-2016 21:06

Downstream channel ID 'slope' ?

Since moving to 16 downstream channels I have been told they're on a 'slope' which means I am seeing on channel ID1 5.6 dB then on ID2 it goes to 5dB then ID3 4.5dB then eventually on CH ID16 I get -0.4dB so I have a high of 5.6 and a low of -0.4 which is the 'slope'.

Does anyone know what causes this and what a tech would do to correct this when they come out?

vm_tech

02-01-2016 21:44

Re: Downstream channel ID 'slope' ?

The higher the frequency the bigger the loss over distance. Although the Docsis frequencies (in my franchise anyway) are all grouped together so there's not normally too much slope across those frequencies. An equaliser or simulator is what wpuld be used to adjust the signal. If you aren't getting any grief I wouldn't worry about it too much!

jb66	02-01-2016 21:54

Re: Downstream channel ID 'slope' ?

Nothing to correct, all signals are in spec

SnoopZ

02-01-2016 22:03

Re: Downstream channel ID 'slope' ?

Thanks guys for the input.

I am on the SH3 trial so it is the guys on the VM forum that are sending an engineer out next week to take a look, as they were not happy with the slope.

DJSADERS

02-01-2016 23:26

Re: Downstream channel ID 'slope' ?

The difference cannot be greater than 8db from the high to the low... This is the "In Spec" levels, i wouldn't take the modem readings as guranteed (but then i'm lucky enough to have a meter to manually measure)
It can cause issues if it is higher than this

vm_tech

02-01-2016 23:53

Re: Downstream channel ID 'slope' ?

The high to low you are referring to will be for the whole spectrum, the OP 5db slope is over 16 frequencies more than like all close to each other. The issue with being told the slope can't be greater than xDB as a generic guideline is all wrong really. The network I work on is 750 network, some areas are 862 and some are 1ghz. That's a lot of difference to have to accommodate with a generic "rule"

DJSADERS

03-01-2016 00:02

Re: Downstream channel ID 'slope' ?

The slope i have to measure to "balance" frequencies if you like are a highend digital (in my case 715 (and sometimes 835) and a low digital 171.

So could be a completely different slope then...

jb66	03-01-2016 07:37

Re: Downstream channel ID 'slope' ?

Quote:

Originally Posted by DJSADERS (Post 35815344)

Id trust the modem more than the old red SLM meters we are given :)

DJSADERS

03-01-2016 09:07

Re: Downstream channel ID 'slope' ?

Quote:

Originally Posted by jb66 (Post 35815353)

Id trust the modem more than the old red SLM meters we are given :)

Fair play, i saw one of the new meters the other week (PT has one) which can measure everything, awesome bit of kit but they wont be issued as standard which sucks

SnoopZ

03-01-2016 09:48

Re: Downstream channel ID 'slope' ?

So these are my levels, so all an engineer would do is screw an equaliser onto the back of the modem to stop the slope, would it cause me any negative power issues?

Tried to copy and paste and reformat but this is the best it came out!

Quote:

Channel Frequency(Hz) Power(dBμV) SNR(dB) Modulation Channel ID
1 243000000 3.4 40.3 256 qam 6
2 323000000 -0.2 38.9 256 qam 16
3 315000000 0.2 38.9 256 qam 15
4 307000000 0.7 38.9 256 qam 14
5 299000000 1.5 40.3 256 qam 13
6 291000000 1.7 38.9 256 qam 12
7 283000000 2 40.9 256 qam 11
8 275000000 2.4 40.3 256 qam 10
9 267000000 2.7 40.3 256 qam 9
10 259000000 3 40.9 256 qam 8
11 251000000 3.2 40.3 256 qam 7
12 235000000 4 40.3 256 qam 5
13 227000000 4.4 38.9 256 qam 4
14 219000000 4.8 40.3 256 qam 3
15 211000000 5.3 40.3 256 qam 2
16 203000000 5.9 38.9 256 qam 1

jb66	03-01-2016 13:19

Re: Downstream channel ID 'slope' ?

Quote:

Originally Posted by SnoopZ (Post 35815365)

I would do absolutely nothing an close the job as No Fault Found, having a slope isnt a fault.

You probably have a long drop on RG6 cable which would show a low upstream too

---------- Post added at 14:19 ---------- Previous post was at 14:11 ----------

Quote:

Originally Posted by DJSADERS (Post 35815360)

Fair play, i saw one of the new meters the other week (PT has one) which can measure everything, awesome bit of kit but they wont be issued as standard which sucks

Id rather have an upstream meter than the most expensive PDA on the market/

I made my own upstream meter, I bought one of these
http://www.ebay.co.uk/itm/Black-Two-...0AAOSwYHxWQ50B

Then cut a SH1 PSU plug and scotched it to the holder and use red tools

DJSADERS

03-01-2016 19:01

Re: Downstream channel ID 'slope' ?

I thought they were issuing SHUB testing kit with built in batteries to the in-house lot?

Kushan

04-01-2016 14:29

Re: Downstream channel ID 'slope' ?

Quote:

Originally Posted by DJSADERS (Post 35815446)

I thought they were issuing SHUB testing kit with built in batteries to the in-house lot?

Who told you that? News to me (On the trial).

jb66	04-01-2016 15:44

Re: Downstream channel ID 'slope' ?

Quote:

Originally Posted by DJSADERS (Post 35815446)

I thought they were issuing SHUB testing kit with built in batteries to the in-house lot?

Basicaly it will be what I have made above but in a fancy case, :erm:

Ignitionnet

04-01-2016 17:45

Re: Downstream channel ID 'slope' ?

Quote:

Originally Posted by Kushan (Post 35815575)

Who told you that? News to me (On the trial).

Note the 'in-house' part of the statement. As in own directly employed staff, not customers.

All times are GMT. The time now is 22:28.

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