Specifications

Example 1: The ES10Xla-PD84 is specified for 84 TV channels. The nominal input level
voltage per carrier is 80 dBµV which corresponds to an input level power of -28.7 dBm
for one unmodulated channel only. For 84 unmodulated channels the total input level
will be –9.5 dBm.
-25,
The specified, guaranteed AGC range of the ES10 is +3 / -6 dB. The recommended
standard input level range is therefore 77 ... 86 dBµV per channel or -12.5 ... -3.5 dBm
total input power.
-30,
0 1
Total rms input power for n unmodulated channels with 80 dBµV
00
00
-20,00
-15,00
-10,00
02030405060708090100
channel count n
total rms power in dBm
In reality, however, the non-guaranteed AGC range, will be significantly larger, typically
about +5 / -8 dB allowing total input level powers of about –14.5 ... –1.5 dBm to be
accepted without input power alarms.
Example 2:
If the transmitter is only operated with 60 unmodulated channels, all with 80 dBµV, the
total input power level can be determined to be –11 dBm, therefore –1.5 dB below the
specified total rms input power. This level is still well within the AGC range of the
transmitter. If the modulation of the carriers is switched on, however, the power of
each modulated carrier drops by about 4 dB. In this case the total power also drops by 4
dB to –15 dBm.
This –15 dBm is even below the extended AGC range and an input level alarm will be
generated. In order to get back into the AGC range, an increase of the input level to at
least –9.5 dBm (unmodulated carriers) is recommended, which corresponds to 81.5 dBµV
in this example. It would even be beneficial to also compensate for the drop of the total
input power due to the AM modulation which in most cases is about 4 dB. In this case
an input level of 85.5 dBµV would be requested per carrier.
If the input power is lower or higher then required, the input LED lights yellow and a
warning is generated. If the input power is missing, the input LED lights red and an
alarm is generated.
The AGC always tries to maintain the requested optical modulation index. The
modulation index determines the amount of bit errors, which come up due to
overmodulation (clipping) of the transmitter.
The subsequent diagram shows the relationship between OMItotrms and the bit error
rate (BER) measured for QAM64 transmission. Obviously, OMItotrms should be below
about 20% in order to obtain BERs better than 10
-6
.
Funea Broadband Services bv product information page 22 of 31
version: 11-02