Small, programmable, high speed PCM subsystem, supports the variety of signals inherent in sophisticated equipment. A signal generated by a transducer is first conditioned to the proper signal range, then sampled by an external multiplexer or by the subsystem directly and then converted and transmitted to a receiving station

Bradanini, P. A.

Kluth, J. T.

English

NASA Technical Reports Server

Sub-
Commutator 
Lj 
Digital 
Multiplexer
7OPGC 
-	
Outputs 
PAM Input 
48 Analog 
Signal Inputs 
PCM Subsystem 
B Digital 
Signal Inputs 
March 1968	 •	 Brief 68-10106 
NASA TECH 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 2215 L, 
'-'-I 
Portable Pulse Code Modulation (PCM) Subsystem 
Transducer 
Transducer 
Transducer
IPPS 
I	 Timing 
Source L1.2KC 
	
atai	 i 
I Analog Signal
Rate	 I Major 
	
Timing I	 I Frame 
Conditioner	
Sub Frame Sync
	
i	 Sync. 
--1	 ----' I I 
thalog Signal 
onditioner 
Digital Signal 
Multiplexer
-	 Control Bit	 f 
	
L ---------
	 Timing 
Data 
Three problems existed in earlier PCM subsystems,	 by a transducer is first conditioned to the proper sig-
minimal data handling capability, fixed format, and	 nal range acceptable to the subsystem. The signal is 
system size, which could not always be tolerated. A	 then sampled by an external multiplexer or by the sub-
PCM subsystem which is programmable, high speed, 	 system directly. The sampled signal is then converted 
and small is required to support the variety of signals 	 by the subsystem and transmitted in a PCM format to 
inherent to a sophisticated spacecraft, for example. 	 a receiving station for data handling and display. 
This PCM subsystem, hereinafter known as the sub- 	 All timing used for sampling signals is generated 
system, is capable of meeting the above requirements. 	 (and thus synchronized) by the subsystem. This timing 
The subsystem is used in the manner shown in the	 is derived from an external timing source supplying 
figure. A signal, event (on-off) or analog, generated	 both 51,200 Hz data rate timing, and I pulse per 
I
s(co ti ued verle 1 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000106 2020-03-12T05:26:15+00:00Z
second Major Frame Synchronization (MFS) signs. 
The MFS controls overall systems' synchronization. 
A conditioned MFS is generated by the subsystem for 
synchronization of all multiplexers. 
The subsystem contains a timer or programmer with 
patchboard, high rate analog gates, an analog-to-
digital converter, digital gates, and a parallel-to-
serial converter. 
Three types of data can be handled by the sub-
system; Pulse Amplitude Modulation, direct analog, 
and digital. Each is converted in programmed 
sequence which is controlled by the timer and pre-
patching. The timer outputs, Primary Gate Controls 
(PGC), are patched to output drivers for control of 
external multiplexer sampling, and also to the internal 
high rate sampling analog gates. 
The sampled analog data is converted into 8-bit 
digital code by the analog-to-digital converter and 
transferred to the parallel-to-serial converter where it 
is "interleaved" with the sampled digital data. The 
control of data conversion, analog or digital, into the 
PCM format is directed by the control bit, an ex-
ternally supplied synchronization signal. Sampling 
rate and position of data in the PCM format is com-
pletely flexible with use of the PGC patchboard and 
control bit. 
The subsystem is a vast improvement over past fixed 
format systems, mainly due to its format patching cap-
ability. Also, its capability of handling the three popu-
lar forms of sampled data simultaneously would 
normally require at least two earlier systems. Finally, 
its size, less than 0.75 cubic foot, and high speed, 
51,200 bits per second, makes the subsystem very use-
ful for a variety of telemetry systems' requirements. 
Notes: 
1. This subsystem has been reduced to practice and is 
being used in the sophisticated and complex Apollo 
spacecraft. 
2. The subsystem is capable of handling 128 channels 
of analog and digital information and would be 
useful for the accumulation of data from many 
points for computer processing or real time display. 
3. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Manned Spacecraft Center 
Houston, Texas 77058 
Reference: B68-10106 
Patent status: 
No patent action is contemplated by NASA. 
Source: P. A. Bradanini and J. T. Kiuth 
of North American Aviation, Inc. 
under contract to 
Manned Spacecraft Center 
(MSC-11369) 
Brief 68-10106
	
.	 Category 01


Portable Pulse Code Modulation /PCM/

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