Performance of high rate telemetry stations used in the Deep Space Network is verified. Measurement techniques are discussed

Burt, R. W.

Ham, N. C.

Reid, M. S.

Sterlzried, C. T.

English

NASA Technical Reports Server

1972	 B72-10089 
NASA TECH BRIEF 
NASA Pasadena Office 
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be directed to the Technology. Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Accurate Measurement of Telemetry Performance 
The performance of the high-rate telemetry sta-
tions used in the deep-space network had to be 
verified. For this purpose, the word-error rate of the 
demodulated telemetry as a function of the RF-input 
signal-to-noise ratio was considered to be a measure 
of performance, but available methods could not 
provide the required accuracy of measurement. For 
example, preliminary considerations indicated that 
the accuracy required would have to be better 
than 0.44 dB at a signal-to-noise energy per-bit ratio 
of 3 dB. 
The entire high-rate telemetry function was in-
cluded by introducing the test signal at the S-band 
carrier frequency. The carrier is converted to an 
intermediate frequency of 10 MHz by the receiver 
and is further processed by the telemetry demod-
ulator assembly. The side-band modulation index 
of the S-band test signal is first adjusted for a 
specific sideband-to-carrier ratio. Then a signal-to- 
noise energy per bit is determined which will pro-
duce a desired word error rate in the demodulated 
data. Next, the carrier-to-noise ratio is set to give 
the required sideband-to-noise energy ratio when 
modulation is applied. Finally, modulation is applied, 
and the performance of the high-rate telemetry func-
tion is judged by the word error rate of the output 
bit stream. It is important to establish accurately 
the signal-to-noise ratio and modulation index used 
in the test. 
The output demodulated data error rate depends 
on four fundamental parameters. The general equa-
tion for effective sideband signal-to-noise ratio is: 
II = [ST./No] (1) (m) (n) (p)
where 
R = effective sideband signal-to-noise energy ratio 
per bit. 
STB/NO = input sideband signal-to-noise energy 
ratio per bit required for the test. 
1 = degradation caused by inaccuracy in setting 
the carrier-to-noise energy ratio. 
M = degradation caused by inaccuracy in setting 
the subcarrier modulation index. 
n = degradation caused by the IF reference error. 
p = degradation caused by phase errors in the 
telemetry demodulation assembly, including 
subcarrier reference error, bit synchronization 
error, and bit detection errors. 
The parameter p is determined during subsystem 
testing and has a design goal of 0.2 dB; n, a function 
of signal level and modulation index, is the result of 
signal processing between S-band and the telemetry 
demodulator assembly and has a design goal of 
0.1 dB. A test accuracy goal has been established for 
each of the other two parameters. This goal is 
0.1-0 maximum degradation when the probability 
of word error for the output bit stream is 0.01. 
Note: 
Requests for further information may be di-
rected to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP72- 10089 
S(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned .rights.
https://ntrs.nasa.gov/search.jsp?R=19720000089 2020-03-17T03:25:12+00:00Z
Patent status: 
No patent action is contemplated by NASA. 
Source: Roger W. Burt, North C. Ham, 
Charles T. Stelzried, and Macgregor S. Reid of 
Caltech/JPL
under contract to
NASA Pasadena Office 
(NPO-11457)
Category 02


Accurate measurement of telemetry performance

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