nanoTX
TM
Telemetry Transmitter
13
Quasonix, Inc.
For example, the transmitter has two encoders, one for in-phase (“I”) data and one for quadrature (“Q”) data. Call
the input symbol stream I0/Q0, I1/Q1, … . Each encoder outputs 2 bits for every input bit, so call the output bit
stream from the first convolutional encoder I0(1), I0(2), I1(1), I1(2), … , and call the output bit stream from the
second convolutional encoder Q0(1), Q0(2), Q1(1), Q1(2), … . Combining the outputs of the two encoders, then,
the output symbol stream is I0(1)/Q0(1), I0(2)/Q0(2), I1(1)/Q1(1), I1(2)/Q1(2), … .
For modes that do not employ Quadrature modulation, such as PCM/FM, Multi-h CPM, and BPSK, only a single
encoder is used.
A single encoder is implemented exactly as described in the “Consultative Committee for Space Data Systems,
Recommendation for Space Data System Standards, TM Synchronization and Channel Coding, CCSDS 131.0-B-1,
Blue Book, September 2003, Section 3.”
A basic convolutional encoder block diagram, as illustrated in CCSDS 131.0-B1, is shown in Figure 2.
Figure 2: CCSDS 131.0-B-1 Rendering of Basic Convolutional Encoder Diagram
1.2.14 Clock-free Baseband Interface Option
– CF
Clock-free is an optional mode that transmits user data, but uses an internal bit sync to take the place of the normal
external clock. The standard TIMTER™ requires external clock and data inputs. With the CF option, no external
clock is required. The clock is generated directly from the data and a user-specified bit rate.