User's Manual

Screen Service SDT ARK 1 ECHO Operations
Jan, 2012 v 1.ATSC_FCC Page 3 - 132
3.20 AUTOMATIC FREQUENCY CONTROL
The Television Broadcasting through countrywide transposers networks requires special care to
avoid too high frequency drift errors.
The Automatic Frequency Control is highly recommended for transposers chains. The following
figure illustrates an example of when the AFC might be used to stop the overwhelming increase
of such errors.
Figure 39. TROVA NOME
The Automatic Frequency Control in ARK1 devices is software defined.
Most of the frequency drift errors could be avoided by means of a stable frequency reference,
such as GPS, but since it is not always available, the ARK1 AFC makes it possible to
compensate frequency jitters owing to each previous transposer.
Frequency compensation of analog input signals is performed through a proprietary algorithm
that, filtering the input video carrier, allows the control loop to extract frequency jitter information
from the input RF phase deviation.
The frequency error adjustment slows down within 3 Hz; it takes about 2 minutes to fulfil the
correction.
 Frequency resolution: 1Hz.
Maximum frequency compensation: 4,000,000 Hz.
Frequency compensation of digital input signals is carried out through frequency jitter
information coming from STV0362 receiving the HP Transport Stream.
 Frequency resolution: 1kHz.
 Maximum frequency compensation: 83kHz.
Due to the Symbol Rate error compensation of the frequency measure algorithm of STV, digital
AFC can work properly only with 0ppm Symbol Rate errors in the input signal.
D
C
A
TX
B
CH 22
CH 22
CH 60: X
CH 36
CH 60: X
CH 36
CH 40
Transposer
Transposer
Teansposer
E
CH 21
Transposer
CH 40