Netxpress Lx Timing Scenarios - Harris CM-30 Installation & Operation Manual

2 –Functional Design
variation. When a subordinate system derives timing from the master, clock recovery algorithms are
employed to align clock frequency and control packet jitter/wander. Also, in order to recover timing
from a stream, the stream must be active and sending. Networking or router problems can result in
no timing recovery from a stream.
Note: When you configure several receive streams and use a stream as the timing source, you
should use the stream with the highest packet rate (such as the lowest frames per payload
value) as the primary timing stream.
2.7.1.4 SynchroCast3™ Timing
The SynchroCast3 system uses a simulcast technique which transmits to an extended geographic area
using multiple, overlapping transmitters operating on the same frequency. Historically, broadcasts
from nearby transmitters on the same frequency have created serious reception problems where they
overlap. The SynchroCast system, originally developed for use in land mobile radio systems, makes
simulcasting possible in FM broadcast as well. The SynchroCast system can provide dramatically
increased station coverage while reducing or eliminating unwanted artifacts at the listener's receiver.
The SynchroCast3 system in the NetXpress LX multiplexer maintains the phase alignment of the
transmitted signals using Global Position System (GPS) technology, providing
● GPS controlled carrier frequency synchronization.
● GPS controlled precision audio phase alignment.
● Dynamic adjustments to compensate for network routing changes.
The SynchroCast3 system sends timing reference signals along with the audio content to the
transmitter sites. GPS receivers, placed at the Origination Point and transmitter sites, provide a timing
reference. At the Transmitter, timing signals coming from the Origination Point (along with the audio
content), are compared with the local timing reference and a precise amount of delay is introduced to
correct the timing difference between transport paths. Once the signals are synchronized, the system
operates automatically to keep the preset delay constant. The Intraplex SynchroCast3 System
Installation and Operation Manual gives more information on the SynchroCast3 system.
The SynchroCast3 system carefully controls the receive jitter buffers associated with the IP streams,
allowing multiple locations to deliver their stream data at precisely the same instant. This control is
essential for radios using multiple transmitters so that interference problems associated with them can
be minimized.
2.7.2

NetXpress LX Timing Scenarios

In a system that utilizes multiple NetXpress LX units deployed on an IP network, it is important to
maintain consistent synchronization of the internal NetXpress LX system clocks. This synchronization
ensures that any NetXpress LX system can receive streams generated by any other unit or a
combination of streams from any other units (Figure 2-4).
Harris Corporation
Intraplex Products
NetXpress LX & CM-30 Installation & Operation Manual
Version 1, September 2010
2-13