User Manual

- an error in the input signals is present (input TS missing and Mute on input error feature enabled).

In the first condition, the output is muted to protect valuable internal parts of the equipment and/or save

power. In the second condition, the output is muted because the signal is most probably unusable by receivers.

This muting action is known as Squelch.

In a dual drive or 1+1 transmitter, the changeover control unit should discriminate if the output power reduction

is caused by a hardware problem (the changeover takes place) or by an input signal problem (the changeover

is not performed). The user can change the meaning of the digital output in the TLM port choosing "Alarm"

(useful to interface a custom remote control system) or "Squelch" (useful to interface a changeover control

unit).

1.4.2 SYNCHRONIZATION AND CLOCKS

The ATSC TRANSMITTER includes its own clock and synchronization generator. A high stability 10MHz

VCTCXO provides the internal clock reference to the clock system of the digital processing section of the

equipment. An external 10MHz reference may be used if a higher stability is needed, or if there is a need to

lock the modulator processing clock or the output carrier frequency to an external reference (i.e. operation in

frequency offset mode).

In special cases, the 10MHz internal clock may be locked to the system clock embedded into the ASI/

SMPTE input signal. In this case, you can not enable the Bit-Rate Adaptation function and the input bit rate

has to be the exact ATSC bit-rate (19.392658Mbit/s). If the ATSC TRANSMITTER is set up to operate

with either of the two external references (from ASI/SMPTE input or from the external 10MHz reference), it

will automatically switch to the internal reference if the external reference is missing. The switching from the

external 10MHz reference to the 10MHz internal clock is totally seamless. The processing clock of the

numerical section of the ATSC TRANSMITTER is always locked to the internal or to the external 10MHz

reference.

1.4.3 OUTPUT SIGNAL

The ATSC TRANSMITTER output signal is available at the output labelled RF OUT on a 50Ω N-type

female connector. The frequency of the output signal can be set in the VHF and UHF bands, depending on the

model type. The frequency can be set by choosing the standard/channel/offset combination (for example,

UHF standard, channel 45 and offset 0Hz) or by choosing directly the center frequency of the output signal.

An attenuated version of the output signal is available at the RF Monitor terminal located on the front panel of

the equipment. The maximum nominal output level is 5W RMS, the output power level can be controlled in

AGC (Automatic Gain Control) mode or in manual mode and can be adjusted by the rotating knob located

on the front panel. The output signal may be muted either manually by the user or automatically depending on

some given conditions. The mute can be direct (abrupt muting) or progressive (linearly decreasing function).