Cable RF Specifications & Troubleshooting

Name

Thresholds

Description

Frequency

DOCSIS 2.0
88-860Mhz Downstream
5-42Mhz Upstream
DOCSIS 3.0
108 to 10002Mhz Downstream
5-88Mhz Upstream

Frequency at which each Channel is connected to

Down/Forward Power (dBmV)

-11 to 11 (Rogers)
-15 to 15 (Cogeco)
-10 to 10 (Preferred)
-15 to 15 (DOCSIS)

Perceived Signal Volume coming into modem from node

SNR (MER)

32dB+ (256QAM)
25dB+ (64QAM)

Clarity of incoming signal vs noise on line as perceived by modem

BER

Ratio of transmission errors vs good transmissions

Correctables

0 to Infinity

# of recoverable transmission failures

Uncorrectables

# of unrecoverable transmission failures
Seeing a value here is fine, as long as the value doesn’t increase during operation

Up/Return Power (dBmV)

This varies by modem – see the modem’s tech specs for details.

Volume of signal being sent by modem

Each Downstream/Forward path channel supports a data rate of 42.88Mbps
Each Upstream channel supports a data rate of 30.72Mbps

Total downstream power should not exceed 30dBmV this is across all channels being broadcast.

In any case check the following:

Connected directly to the cable drop?
Connected to Wall Jack?
- If house, then most likely is split off in basement
- If Apartment building, then this is the cable drop.
In good condition
- No cracks/breaks
- Cable securely connected to crimp on connector
- No staples
RG6
- RG6 cable is for digital signal
- Older houses/installations might use RG59 which will work ok but if getting low SNR then try replacing with RG6

Splitters
- Need to be for Digital Cable 5Mhz-1000Mhz
- Should only be used if service needs to be split for Cable TV or Rogers/Cogeco digital phone
- Replace with couplers (F81 connectors) or remove where possible
Couplers (F81)
Filters
- Used to block certain frequencies (Normally cable TV)
Attenuators
- Increases resistance/attenuation on line
  - Strength of attenuator will be printed on it. 3dB/6dB etc
- Reduces forward power coming into modem
- Increases return power.
Amplifiers
- Needs to be 2 way, have return gain, or say designed for cable internet
- Passive return will only amplify Forward Path Power and the modem’s return power will then max out.
- Amplifiers should only be used if installed by cable tech.

Modem	Power Supply Name	Power Specification
Thompson DCM475/476	Leader Electronics OEM	12v 1.0a
TC4300	Leader Electronics	12v 1.0a
Motorola SB6121	Leader Electronics	12v 750ma
Hitron CDA3	Asian Power Devices	12v 1.5a
SmartRG SR804	Switching Adapter Shenzhen GongJin	12v 2.0a
Others		See input on modem

See Also: