Echo device method for locating upstream ingress noise gaps at cable television head ends

A cable modem device configured for use in a variable carrier frequency loop testing system, the device comprising:

• a demodulator for receiving and forwarding a downstream test packet wherein the test packet has a media access control address of the cable modem device;
• an address manipulation device which replaces the media access control address of the cable modem device with a media access control address of a test packet checker device without modifying any other portion of the test packet;
• and
• a modulator for transmitting the test packet upstream to the test packet checker.

A method of identifying a transmission frequency for transmitting digital data upstream in a cable system, said transmission frequency having relatively less noise than at least some other frequency bands, the method comprising:

• (a) selecting a test frequency;
• (b) transmitting test data at a downstream frequency, the test data being addressed to an echo device located downstream on the cable system;
• (c) receiving test data sent by said echo device at the test frequency;
• (d) determining a noise level associated with the test frequency by evaluating the received test data;
• and
• (e) repeating steps (a) through (d) for a plurality of test frequencies to identify the transmission frequency.

A method of identifying a frequency channel for transmitting digital data upstream in a cable system, the method comprising:

• (a) selecting a test frequency;
• (b) generating a test data stream containing a plurality of bits;
• (c) transmitting said test data stream from a second point on the cable system downstream to a first point on the cable system;
• (d) receiving said test data stream at the second point located upstream from said first point on the cable system;
• (e) evaluating the condition of said test data stream at said second point to assess a noise level at said selected frequency;
• (f) repeating steps (b) through (e) for a plurality of test frequencies;
• and
• (g) determining which of said plurality of test frequencies contains the least noise.