User Manual

VCom Inc.

AP5857 Manual; ml_ap5857_08 (Oct 2005)

Approved: R.B.

This setting allows the user to set the length of the interleaver for the downstream modulation. Valid inputs

are 128,1; 64,2; 32,4; 16,8; and 8,16. To change the Downstream interleaver length, type “4”. The local

interface prompt will change to:

Downstream Interleaver[128,1 64,2 32,4 16,8 8,16](16,8) _

Enter the new interleaver length or press ENTER to use the current value. The values entered into the

interleaver represent the I,J values in the convolutional interleaver. Longer lengths such as 128,1 provide

more protection against burst errors since it spreads the errors out over a longer period of time, and it is more

likely that the error correction can correct them. The cost is an increased delay time. For the longer

interleaver depths, it is possible that the cable modem will be unable to lock due to delay limits set in the

CMTS, so they should be used with caution. The AP5857 is shipped with the interleaver set to 16,8 which

provides adequate protection while keeping delay low. Delays from the interleaver vary (for 64/256QAM)

from 8/5.6 ms for 128,1 to 0.44/0.30 ms for 8,16. The cable modem at the subscriber side will automatically

adjust to the selected interleaver value.

Downstream Output Mute

This setting allows the user to mute the downstream output. If the setting is set to muted, the output will

remain muted until the setting is changed to “unmuted” and no alarm condition exists.

To change the Downstream Output Mute state, type “4”. The local interface prompt will change to:

Output Mute [0 unmute, 1 mute](1)>_

Enter the new value or press ENTER to use the current value.

Downstream CATV Frequency

This indicates the center frequency of the downstream CATV channel to which the radio is tuned. This value

is automatically configured by the radio to match the internal cable modem downstream frequency. Note that

the value can not be changed directly by the user. The user may either let the internal cable modem lock on

to a channel by itself, or the configuration file for the modem used by the CMTS may be written to direct the

cable modem to a specific downstream channel. If the cable modem is not locked to a valid channel, the

Input Frequency will indicate “No Channel”

Downstream Demodulator Status

Indicates the lock status of the downstream demodulator. It will display Locked or Not Locked. If the

demodulator is not locked, this may indicate that there is no valid signal or the signal quality is too low for

proper operation. Check also that the modulation (64QAM or 256QAM) is set to the correct value.

Downstream Demodulator SNR

Indicates the estimated downstream Signal to Noise Ratio as seen by the demodulator. The best signals will

result in SNR values of 35 dB or more, however good operation will be maintained to SNR values of 30 dB or

less. Lower SNR values indicate poor signal conditions, which may include interference or low signal level.

The indicated SNR is an instantaneous reading, so the value of the SNR will vary from reading to reading.