Demodulator; Dmd15/Dmd15L Clocking Options; Scte: Serial Clock Transmit External; Sct: Serial Clock Transmit - Radyne DMD15 Installation And Operation Manual

DMD15/DMD15L IBS/IDR Satellite Modem

3.10.2 Demodulator

The demodulator performs a complete digital implementation of a Variable-Rate Phase-Lock
Satellite Receiver utilizing state-of-the-art digital signal processing techniques. The demodulator
is capable of receiving nearly any modulation format. Signals enter the demodulator, are
converted to baseband, split into 'I' In-Phase and 'Q' Quadrature Channels and digitized. The
digitized I and Q Channels are then applied to a decimating FIR Matched Filter. After filtering, the
signal is demodulated using a Costas Loop for recovery of the carrier and a clock recovery loop
for recovery of bit timing. The demodulated data is then fed to a 1650 Viterbi Decoder, or
Sequential Decoder if the option is installed. After decoding, the data is differentially decoded and
descrambled.

3.11 DMD15/DMD15L Clocking Options

The following paragraphs define the types of clocking options available to the user at the Front
Panel of the DMD15/DMD15L:

3.11.1 SCTE: Serial Clock Transmit External

This clock is the Transmit Terrestrial Clock associated with the interface. With the G.703
Interface selected, SCTE is the clock that is recovered from the G.703 data stream. SCTE is
sometimes referred to as Tx Terrestrial Timing and for Synchronous Interfaces such as RS-422,
SCTE is sometimes referred to as TT (Terminal Timing).

3.11.2 SCT: Serial Clock Transmit

This clock is an internally generated clock that is output from the modem. The clock is generally
used by the Terrestrial Terminal equipment for clocking the transmit data. The frequency of the
clock is set the same as the Transmit Terrestrial Clock rate if internal is selected, or is the receive
clock from the Demodulator if SCR is selected. SCT is sometimes referred to as Internal Timing
or ST (Send Timing).

3.11.4 EXT EXC: External Clock

This is an independent clock source. This clock is most often used if there is a station master
clock. The EXT EXC can be selected, in the Interface/General Menu, to be balanced, bnc exc,
sys rcs10, or IDI. IDI is used ONLY for D&I cases where external framing is selected. In this
case the EXT EXC must be set to IDI where the Receive Buffer Clock is derived from the external
Receive T1 or E1 Trunk.

3.11.5 BNC EXC: BNC External Clock

Unbalanced external clock input into BNC Connector J5.
Clock specification:
Frequency:
Level:

3.11.6 BAL EXC: Balanced External Clock

This clock is input into J8-15-33, J7-7-8, or J18-13-47; all connectors are wired together for this
clock and so only one connector pair should be driven at one time. The clock must meet RS-422
levels.
TM051 - Rev. 5.8
1 MHz – 10 MHz in 40 kHz steps
0.5 Vp-p – 5 Vp-p
Operation
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