The shuttle Ku-band Costas loop lock detector output signal appears to vary about the lock detection threshold (the lock detect flag is on and off) shortly after the carrier acquisition starts. Real time computer simulation was performed to obtain the signal output from the low pass filter of the lock detector. Based on this simulation, it appears that the oscillation of in-lock and out-lock is related to tracking process and is not caused by the sweep acquisition algorithm

Chie, C. M.

Lindsey, W. C.

Tsang, C. S.

English

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FINAL REPORT FOR JUNE 1982 TO JULY 1983
ORBITER GLOBAL POSITIONING SYSTEM DESIGN
AND KU-BAND PROBLEM INVESTIGATIONS
EXHIBIT B - REVISION 1
; NASA-CR--171699) ORBITER GLOBAL POSITIONING	 N83-?4928
SYSTEM DESIGN AND Ku-BAND F:ROBIEM
INVESTIGATIONS, EXHIBIT B, FEVISION I Final
Report, Juan. 1982 - Jul. 1983 (Lincom Corp.,	 Unclas
.Los Angeles, Calif.)	 12 p HC A02/MF A01
	
G3/04 42 162
PREPARED FOR
NASA LYNDON B. JOHNSON SPACE CENTER
HOUSTON, TX 77058
TECHNICAL MONITOR. WILLIAM TEASDALE
CONTRACT NO, NAS9-16097
(^O- (^a r
RO, BOX 15897, LOS ANGELES, CALIFORNIA 90015
TR-0783-0980
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FINAL REPORT FOR JUNE 1982 TO JULY 1983
ORBITER GLOBAL POSITIONING SYSTEM DESIGN
AND KU—BAND PROBLEM INVESTIGATIONS
EXHIBIT B - REVISION 1
/.
PREPARED FOR
NASA LYNDON B. JOHNSON SPACE CENTER
HOUSTON, TX
	
77058
TECHNICAL MONITOR:	 WILLIAM TEASDALE
CONTRACT NO. NAS9-16097
•I
PREPARED BY
W. C. LINDSEY I°
C. S. TSANG #
C.	 M.	 CHIE
LINCOM CORPORATION
P.O. 'BOX 15897
LOS ANGELES, CA
	
90015
JULY 1983 d
TR-0783-0980
ZinCom
1,	 Intro
2. Effm
3. Effm
3.1
3.2
3.3
ATTACHMENI
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1. Introduction
This report serves to document the LinCom effort under Exhibit B
of Contract NAS 9-16097 for the period Juno 1, 1982 through July 22, 1983.
The purpose of Exhibit B is to support JSC in its study of the use of
the GPS navigation system on the Space Shuttle Orbiter and in Ku-band
problem investigations.
2. Effort Related to GPS
No effoot related to GPS was made during this part of the contract
performance period because such effort ceased in 1981 under instructions
from JSC.
3. Effort Related to Ku-Band System
3.1 Introducti on
In support of the Orbiter Ku-band System problem investigation,
LinCom was tasked to provide independent technical evaluation of the
system performance evaluations.
3.2 Description of Effort
To fulfill the task requirements, LinCom attended the monthly
Ku-band program reviews at Hughes Aircraft Company and Communications
Gropu in El Segundo, CA, and from the reviews and outside discussions
tinCom became aware of many problem areas. A preliminary assessment
of the problems was provided to the JSC person concerned and later the
problems were followed up.
One exaple of such a problem is the forward-link Costas demodulator
lock indicator blinking problem, documented in Attachment 1. In this
case a detailed analysis was performed
-1-
	
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ATTACHMENT 1
UnCom Corporation
iNTEROFFiC^' MEMORANDUM
TM-1080-118'
Date: November 29, 1982
From: C. S. Tsahg, C. M. Chie
To Jim Ratliff
Sulaject:: Shuttle, Ku-Band Forward Link Costas Demodulator Lock Indicator
Blip ng Problem
Summary
The Costas demod lock indicator blinking problem was verified on
November 15, 1982 at the Hughes Baldwin Hills test facility. The
receiver was visual'ly observed (by monitoring the Costas lock indicator
light) to acquire almost instantaneously 4 out of 4 tests. The carrier-
to-noise ratio quoted was 60 dB-Hz. However, once, the Costas loop had
acquired, the indicator light then went on and off intermittently.
The sweep acquisition scheme was suspected to cause this problem
and an analysis was performed to assess the sweep acquisition scheme.
The results of this analysis, documented in this memo, show that the
peak amplitude of the-low pass filtered voltage input to the threshold
detector during sweeping is about 1% of the in-lock amplitude.
Therefore separate thresholds are needed for acquisition and tracking
lock indications.
Examination of the reference;print (DWG 3555201, Rev. J) showed
that a dual threstiu?d was used. In addition, a soft limiter is employed
apparently to reduce this 1:100 variation in amplitude be
acquisition and tracking.
R	
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It therefore appears . that the blinking problem is a consequence of
the desire to use the tracking threshold to indicate false side-lobe
illumination condition. 	 Apparentl y , the threshold was set to threshold
at the highest expected side-lobe power level.	 This is different from
i
the normal
	 practice of employing the lock indicator to monitor excessive
cycle slip p ing o	 drop-lock.	 a receiver was implemented i
	 ruc	 a wa
	 	 	 r	 	 .	 Th	 	 h	 y
that, unfortunately, when the tracking threshold is crossed, the
receiver goes' to swef::p , acquisition.	 This causes the blinking.
^' A simple solution to this problem is to use the present threshold
detector for conventional out-of-lock indication but then add another
threshold detector for false side-lobe lock monitoring.
Y
1.	 Introduction
The shuttle Ku-Band Costal Loop Lock 'Detec
t
or output signal appears
foto vary about the lock detection tto%esh i d	 (the lock detect flag is on
and off) shortly after the carrier acquisition starts. 	 I i is the
purpose of this memo to study whether this phenomenon is caused by the
sweep acquisition algorithm.
	
Real time computer simulation is performed
to obtain the signal output from the low pass filter of the lock
detector.
	
Based on this simulation, it appear; that the oscillation of
in-dock and out-of-lock is related to tracking process and not to
acquisition.
j! 2•	 Simulation
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2	 2The signal	 x(t) input to the low pa.,ss filter is of the form I -Q ,
where I(t) and Q(t) are respectively output of the in-phase and quadra-
,t phase arm filters of the Costas Loop, fig. 1. 	 During acquisition the
signals I(t) and Q(t) is of the form
d	 ,
-4-
a;
-5-
OCK DETECT
LAG
r	 Figure 1. Costas Loop Lock DetPqtor.
x	
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a(t)	 -	 A cos (27r f t2 +
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where a	 4.4 MHz/sec is the sweep rate of the sweep circuit, and	 is a
random phase error. 	 Therefore x(t) is of the form
x(t)	 A cos(2wat 2 + 2^)
For simplicity, the low pass filter is taken as a RC low pass filter of
3 dB frequency 3.25"liz.
Figs.	 2 to 4 are simulations output for 	 0,	 7r/4 and it/2
radians.	 For all	 cases, the output signal 	 peak is in the order of
6x10 -3A.	 This signal	 amplitude is much less than the tracking threshold
and will	 not cause any on-off oscillation of the lock detector flag.
Therefore,	 it appears that the on-off oscillation is due to the
fluctuation of tracking signal 	 about the tracking threshold.
Distribution
Eli B. Batson
H. Haddad
J. Johnson
J. MacLeod
S. Novosad
J. Seyl
W. Teasdale
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Orbiter global positioning system design and Ku-band problem investigations, exhibit B, revision 1

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