CATV return band sweeping using data over cable service interface specification carrier

1. A method for determining the linearity of a CATV return band comprising:

energizing a cable modem at a subscriber's premises to log in to a Cable Modem Termination System (CMTS) and generate a plurality of active carriers in the CATV return band, each active carrier being a DOCSIS-compliant carrier;

energizing a signal analyzer at the subscriber's premises to receive data from the cable modem;

determining, with the signal analyzer, the transmit carrier frequency, symbol rate, and level for each active carrier of the plurality of active carriers in the CATV return band;

accessing, with the signal analyzer, a transmit carrier ranging error level for each active carrier of the plurality of active carriers in the CATV return band via the cable modem;

accessing, with the signal analyzer, a corresponding number of transmit carrier pre-equalizer filter coefficients that represent an inverted frequency response for each active carrier of the plurality of active carriers in the CATV return band via the cable modem;

adjusting each active carrier of the plurality of active carriers using the corresponding filter coefficient to minimize in-channel amplitude variation;

adjusting a carrier level for each active carrier of the plurality of active carriers by its ranging error and determining an average transmit level for all of the active carriers;

updating a graphical display based on the average transmit level;

determining the in-channel response for each active carrier of the plurality of active carriers in the return band;

generating a return band frequency response at the subscriber's premises using the in-channel response for each active carrier of the plurality of active carriers in the return band, wherein generating the return band frequency response comprises plotting, for each active carrier of the plurality of active carriers, each active carrier's in-channel response on the updated graphical display, and

comparing the active carrier in-channel responses to identify any differences in amplitude and determine the linearity of the CATV return band.

2. The method of claim 1 , wherein adjusting the carrier level for each active carrier of the plurality of active carriers by its ranging error and determining the average transmit level comprises establishing the average transmit level as the zero reference of the frequency spectrum for the CATV return band.

3. The method of claim 1 wherein determining the in-channel response for each active carrier of the plurality of active carriers in the CATV return band comprises using upstream pre-filter coefficients to determine the in-channel response for each active carrier of the plurality of active carriers in the return band.

4. The method of claim 1 , wherein energizing a cable modem to log in to the Cable Modem Termination System (CMTS) and generate the plurality of active carriers in the CATV return band comprising connecting a test instrument comprising the cable modem to a data line at the subscriber's premises and energizing the test instrument.

5. The method of claim 1 , further comprising correcting any difference in amplitude in the return band frequency response to improve the linearity of the CATV return band.

6. The method of claim 1 , further comprising connecting a test instrument include the cable modem and the signal analyzer to a data line at the subscriber's premises.