SB5120 & Comcast Woes

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Subject Author Date
SB5120 & Comcast Woes mediumhappy 12-18-2006
Posted by Ed Nielsen on December 21, 2006, 9:46 am
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If it were me, Tim, I would pad that down by another 6dB, bringing the
downstream down to +3 and the transmit up to around +53dBmV. Only, I
would have ALL of the padding at the splitter that feeds your cable
modem. If it is a splitter, perhaps change that out for a directional
coupler of comparable value. Many engineers like to see cable modems
run out on the hot side. It helps it to be heard over any noise that
might get on the drop. 53 is perfectly fine. DOCSIS specifies a high
end of 58.

Then again, if you have a DCT(digital cable box), the increase in signal
level a DC would give it could cause it some grief. Might have to throw
in a 3dB pad on the THRU leg of the DC.


CIAO!

Ed N.

Timothy Daniels wrote:
> The line technicians were by today, and they said the signal level
> on the downstream side (coming into our property) was a bit high,
> so they padded it down by 4-5 dB. Now the modem is reporting a
> downstram signal level of 9 dBmV and an upstream signal level of
> 47 dBmV. It had been 15-17 downstream and 50-52 upstream.
> I asked the tech who adjusted our amp if those numbers meant
> NEGATIVE dB, but he said no (which may still not mean anything).
>
> The bottom line is that the speeds have increased a bit, but it's
> not really obvious due to the high variance from test to test. Tracerts
> are still showing timeouts, and InternetFrog.com is showing "Quality
> of Service" levels ranging between 9% and 50%, i.e. high retransmission
> rates, and the VOIP test indicates that there would be lots of dropouts
> and pauses. I believe it's due to congestion in the RoadRunner network.
>
> *TimDaniels*
>
>

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Posted by Todd H. on December 21, 2006, 11:19 am
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> If it were me, Tim, I would pad that down by another 6dB, bringing the
> downstream down to +3 and the transmit up to around +53dBmV. Only, I
> would have ALL of the padding at the splitter that feeds your cable
> modem. If it is a splitter, perhaps change that out for a directional
> coupler of comparable value. Many engineers like to see cable modems
> run out on the hot side. It helps it to be heard over any noise that
> might get on the drop. 53 is perfectly fine. DOCSIS specifies a high
> end of 58.

DOCSIS spec or no, in my experience on comcast and wide open west
networks, upstream >50dBmV has always correlated with intermittent
packet loss and frustration like the OP is experiencing. :-)

--
Todd H.
http://www.toddh.net/

Posted by Ed Nielsen on December 22, 2006, 10:25 am
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Been running out at ~52-54dBmV for about 5 years now with no issues.
I'd much rather run at 52dBmV and be able to shout and be heard above
the noise that inherently makes its way into the line than keep my cable
modem running down around 40dBmV.


CIAO!

Ed N.

Todd H. wrote:
>
>> If it were me, Tim, I would pad that down by another 6dB, bringing the
>> downstream down to +3 and the transmit up to around +53dBmV. Only, I
>> would have ALL of the padding at the splitter that feeds your cable
>> modem. If it is a splitter, perhaps change that out for a directional
>> coupler of comparable value. Many engineers like to see cable modems
>> run out on the hot side. It helps it to be heard over any noise that
>> might get on the drop. 53 is perfectly fine. DOCSIS specifies a high
>> end of 58.
>
> DOCSIS spec or no, in my experience on comcast and wide open west
> networks, upstream >50dBmV has always correlated with intermittent
> packet loss and frustration like the OP is experiencing. :-)
>

Posted by Eric on December 23, 2006, 12:42 pm
If you were  Registered and logged in, you could reply and use other advanced thread options

Ed Nielsen wrote:
> Been running out at ~52-54dBmV for about 5 years now with no issues.
> I'd much rather run at 52dBmV and be able to shout and be heard above
> the noise that inherently makes its way into the line than keep my cable
> modem running down around 40dBmV.
>
>
> CIAO!
>
> Ed N.
>
> Todd H. wrote:
> >
> >> If it were me, Tim, I would pad that down by another 6dB, bringing the
> >> downstream down to +3 and the transmit up to around +53dBmV. Only, I
> >> would have ALL of the padding at the splitter that feeds your cable
> >> modem. If it is a splitter, perhaps change that out for a directional
> >> coupler of comparable value. Many engineers like to see cable modems
> >> run out on the hot side. It helps it to be heard over any noise that
> >> might get on the drop. 53 is perfectly fine. DOCSIS specifies a high
> >> end of 58.
> >
> > DOCSIS spec or no, in my experience on comcast and wide open west
> > networks, upstream >50dBmV has always correlated with intermittent
> > packet loss and frustration like the OP is experiencing. :-)
> >

If you are in an area fed from poles (aerial), go outside and follow
your drop to the line. You will see a small box called a tap. There
should be a number showing. Subtract that number from your modem
transmit level. Then subtract 3 dB for every 2-way splitter, 7dB for
every 4 way and 11dB for every 8 way in the line between your modem and
the tap. Subtract 1dB for every 100' of coax. The remainder should be
equal to between 15 and 20dB (most systems that were rebuild by AT&T
Broadband should be about 17dB).

Example:
26-4 tap
4 way splitter
150' drop
50' run to outlet
17dB amplifier drive level
modem should transmit at 52dB

Usually, systems are designed to make modems run about 45-50dB. Lower
value taps (further away from an amp) take into account increased cable
loss, splitters, and other devices. The tap in the example above will
be directly connected to an amplifier.


Posted by Poul Starz on December 21, 2006, 2:48 pm
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He's not likely to answer for awhile as the RR news servers have
been down for 5 days of "maintenance" with no estimated-time-
of-completion given. TW has been *ucked up for a couple months
since absorbing Comcast and Adelphia customers in November.
--------------------
***PoulStarz***

> If it were me, Tim, I would pad that down by another 6dB, bringing the
> downstream down to +3 and the transmit up to around +53dBmV. Only, I
> would have ALL of the padding at the splitter that feeds your cable
> modem. If it is a splitter, perhaps change that out for a directional
> coupler of comparable value. Many engineers like to see cable modems
> run out on the hot side. It helps it to be heard over any noise that
> might get on the drop. 53 is perfectly fine. DOCSIS specifies a high
> end of 58.
>
> Then again, if you have a DCT(digital cable box), the increase in signal
> level a DC would give it could cause it some grief. Might have to throw
> in a 3dB pad on the THRU leg of the DC.
>
>
> CIAO!
>
> Ed N.
>
> Timothy Daniels wrote:
>> The line technicians were by today, and they said the signal level
>> on the downstream side (coming into our property) was a bit high,
>> so they padded it down by 4-5 dB. Now the modem is reporting a
>> downstram signal level of 9 dBmV and an upstream signal level of
>> 47 dBmV. It had been 15-17 downstream and 50-52 upstream.
>> I asked the tech who adjusted our amp if those numbers meant
>> NEGATIVE dB, but he said no (which may still not mean anything).
>>
>> The bottom line is that the speeds have increased a bit, but it's
>> not really obvious due to the high variance from test to test. Tracerts
>> are still showing timeouts, and InternetFrog.com is showing "Quality
>> of Service" levels ranging between 9% and 50%, i.e. high retransmission
>> rates, and the VOIP test indicates that there would be lots of dropouts
>> and pauses. I believe it's due to congestion in the RoadRunner network.
>>
>> *TimDaniels*
>>
>>

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