Troubleshooting
01-0868-401B 12/02
53
E
b
/N
0
, Carrier Offset,
and Link Margin
Information
Receive Signal E
b
/N
0
The E
b
/N
0
value that the TDR60 displays is the estimated E
b
/N
0
level of the
receive signal in units of dB. This value, when used in conjunction with the DVB
minimum performance requirements, indicates the link margin for the
transmission. An E
b
/N
0
value at least 3 dB above these limits is reasonable. E
b
/N
0
levels that drop near the DVB limits may cause interrupted or poor quality video
service.
If the E
b
/N
0
level is above the minimum DVB requirements, the TDR60 should
acquire the carrier, demodulate the signal, allow the decoder to lock to the
transport stream, and provide decoded video and audio output.
The minimum E
b
/N
0
levels required for successful reception of a signal that will
guarantee flawless video performance at each Viterbi code rate are listed in the
following table.
Carrier Offset
The carrier offset displays a measurement, in KHz, of the difference between the
actual receive carrier frequency and the frequency determined by subtracting the
LO Freq parameter from the RF Freq parameter. To achieve carrier (transport
stream) lock, the difference between the two frequencies, as shown in the Offset
parameter, must be less than 2MHz; however, to achieve optimum performance,
the Offset should be as close to zero as possible.
When the TDR60 is trying to lock onto the receive carrier, the carrier offset
display varies and does not display a single frequency for more than a few
seconds. Once the TDR60 is locked onto the receive carrier, the offset displays a
measurement that indicates the number of Hz that you need to adjust your RF Freq
parameter. To adjust the RF frequency:
1. Check the offset parameter after the TDR60 has locked onto a frequency. To
query the offset, use the
Input>Status>Offset
menu.
2. If the offset is greater than zero, subtract the value of the Offset from the
current value of the RF Freq parameter RF – LO = New RF
3. Enter the difference as the new RF freq parameter.
4. Check the offset parameter again to verify the new value.
E
b
/N
0
vs. Viterbi Code Rate Performance Levels
Viterbi Code Rate
Minimum E
b
/N
0
(dB)
1/2
4.5
2/3
5.0
3/4
5.5
5/6
6.0
7/8
6.4
