VP310

PRELIMINARY DATA

23

2.7 Signal and Performance Monitors

The LNB error frequency can be obtained from LNB_FREQ registers (7 – 8). Any LNB error may

be removed by offsetting the LNB frequency and re-tuning the tuner by the indicated amount.

However, note that VP310 compensates for this frequency error before QPSK demodulation.

Hence it is not necessary to re-tune the front-end unless this LNB error causes a significant

amount of signal energy to be lost due to anti-alias filtering.

The tuner RF signal level indication can be obtained from AGC H and AGC M registers (108 –

109).

VP310 input signal level indication can be obtained from SIG_LEV register (19).

An indication of Signal to Noise Ratio (SNR) can be obtained from M_SNR registers (9 – 10)

where a formula is given. This measurement is only intended as a guide to the SNR of the

channel being received. It should not be taken as the absolute value of SNR.

QPSK output Bit Error Rate is available by dividing the reading from VIT_ERRCNT registers (11

– 13) by the reading from VIT_ERRPER registers (83 – 85).

Viterbi output Bit Error Rate is available by reading RS_BERCNT registers (14 – 16). Two

readings are taken with a known time interval separating them. The first reading resets the

counter at the start of the time period, so it is ignored.

The Reed Solomon uncorrected block error count can be found from RS_UBC registers (17 –

18). This reading is related to the cycle slip performance of the tuner. The measurement

technique is similar to that for the Viterbi Bit Error Rate above, two readings being taken over a

defined time period. In this case the period will usually be very long, say 24 hours, to accumulate

a reasonable count.