Wegener DR95 Instruction Manual page 29

In this section, operation of the Model DR95-1X/DR96-1X Digital Audio SCPC Receiver will be
discussed. Fundamentally, the device solves the basic problem of narrow band SCPC satellite
reception while allowing maximum flexibility in human operator control. Loaded with a factory-
programmed list of desired downlink carriers, the receiver is able to seek out, lock onto, and
identify carriers automatically. This makes it possible to operate the receiver in a simple, local,
manual control-mode or to make it part of a broad point-to-multipoint broadcast network
controlled from the central uplink facility. While it does this, much information about the
receiver and the communications link may be downloaded to the human operator.
General discussion of the receiver operation is divided into four parts: an explanation of the basic
signal-acquisition modes of the receiver, a discussion of receiver operation while tracking a
signal ("normal operation"), an introduction to the front-panel indicators, and a summary of the
control and reporting methods.
3.1 AQUISITION MODES
A fundamental problem of narrow band SCPC satellite reception is that of signal acquisition,
because the frequency offsets in the link (presumed to be mostly on the receive side) may be
many times greater than the signal bandwidth. In addition, many such carriers may lie in the
vicinity of the desired carrier. Thus, the problem of acquiring a carrier consists of sweeping the
tuned frequency of the receiver until a carrier is encountered that the demod can "lock" to, then
somehow determining if the carrier encountered is the correct one (and if reception is even
authorized!). Wegener's system for narrow band SCPC satellite broadcast consists of providing
an acquisition aid in the form of a frequency "tag" for all its carriers. This is a short frame of
encoded bytes appearing in the auxiliary data stream of the MPEG-compressed data. It indicates
to the receiver that carrier's nominal downlink frequency.
The following paragraphs explain the various acquisition modes and how the receiver moves
between them. Figure 3-1 graphically shows these modes for the two cases of a non-network-
controlled receiver and a network-controlled receiver.
3.1.1 Installation Mode
At initial power-up, the DR95-1X/DR96-1X receiver retrieves the "permanent carrier frequency"
data stored in its non-volatile memory. This will be the signal it first attempts to acquire
(EXCEPTION: see paragraphs 3.1.4 and 3.1.5). It begins by coarsely tuning near the nominal
center frequency. It then finely dithers that tuned frequency around the starting point in an
expanding search pattern, searching for a carrier the demodulator can lock onto. This pattern's
range will exceed the specified ± 1 MHz Carrier Lock Range (about ± 2.5 MHz). If the receiver's
demodulator locks to a carrier with compatible FEC channel encoding, the firmware checks to
see if the MPEG-compressed audio decoder can find frame synchronization in the output data. If
"MPEG lock" is achieved, the firmware monitors the auxiliary data output of the MPEG decoder,
awaiting a carrier-frequency tag. If a tag arrives, and if it is for the desired signal, acquisition is
SECTION 3
OPERATION
3-1 DR95/DR96-001