The amount of steady state and transient noise which will couple to orbiter CCTV video signal wiring is predicted. The primary emphasis is on the interim system, however, some predictions are made concerning the operational system wiring in the cabin area. Noise sources considered are RF fields from on board transmitters, precipitation static, induced lightning currents, and induced noise from adjacent wiring. The most significant source is noise coupled to video circuits from associated circuits in common connectors. Video signal crosstalk is the primary cause of steady state interference, and mechanically switched control functions cause the largest induced transients

Blanke, L. R.

Lawton, R. M.

Pannett, R. F.

English

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https://ntrs.nasa.gov/search.jsp?R=19770022405 2020-03-22T07:52:42+00:00Z
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MCDONNELL DOUGLAS TECHNICAL SERVICES CO.
NOl!Sl'ON ASTRONAUTICS DIVISION
SPACE SHUTTLE EPGINEERING AND OPERATIONS SUPPORT
1.3-Dii-CO704-039
ORBITER CCTV VIDEO SIGNAL NOISE ANALYSIS
5 AUGUST 1977
This Design Note is submitted to NASA Under Task
Order No. C0704, Contract NAS 9-14960
APPROVED BY: ,^_ /7: . ^ 	 _^	 PREPARED BY: r; 71
A. J. 6irsunger	 --	 R. M. Lawton
Task Manager	 Senior Engineer
488-5660 x 317	 488-5660•x 317
AUG 1977 0
RECEIVED
NASA STI FACILNT ti
INPUT BRANCH
	 1
L. R. Blanke
Technical Manager
488-5660 x 260
R. F. Pannett
Project Manager
4B8-5660- x 258
(NASA-CE-151479) ORBITER CCTV VIDEO SIGNAL
	 N77-29349
NOISE ANALYSIS (McDonne11-Dcug1as
Astronautics CO.) 11 p HC A02/MF A01
CSCL 17B	 Unclas
G3/32 43943
s	 I.
1.0 SUMMARY
This paper predicts the amount of steady state and transient noise ^,jhich
will couple to Orbiter CCTV video signal wiring in the cabin area. The
primary emphasis is on the interim system. However, some predictions
are made concerning the operational system wiring in the cabin area.
Noise sources considered are Rf fields from on board transmitters,
precipitation static, induced lightning currents, and induced noise
from adjacent wiring. The most significant source is noise coupled
to video circuits from associated circuits in common connectors.
Video signal crosstalk is tine primar -e cause of steady state interference,
and mechanically switched control functions cause the largest induced
transients.. Worst case crosstalk is 2.3 millivolts peak to peak for
^a
the interim system and 18.4 millivolts for the operational system.
The worst case transient coupling is 149 millivolts for both systems.
(..	 The analytic technique utilized is based on coupling equations. described
s!
in Design Note 564 of AFSC Design Handbook DH1-4 (Reference 1).
i
The results are considered to be worst case.
The significance of the predicted noise levels is not apparent since
there is no specified allowable video noise. Therefore, it is recommended
that a test be performed to inject known noise levels using existing
hardware and subjectively evaluate picture quality degradation.
An alternative would be to compare any noise level measurements on
video signals of past programs to the predicted levels of this paper.
i__1 _.11.1 ._ _.
I,
2.0 DISCUSSION
It is intent of this design note to assess the noise pick-up on the
interim TV system video signal routed through the orbiter cabin area.
In addition, noise pick-up on the same circuits will be examined
for the operational TV system.
The video signal wiring to be analyzed consists of the following;
Flight Deck Panel 019 (30J9192) to the VIU	 (Video Interface Unit)
' (30 P6),	 Mid Deck Panel M058 (8OP9701) to the VIU (30 P6),	 and VIU
(30	 P6),	 and	 VIU (30P6) to the S-Hand FM Signal	 Processor	 (83P76).
Noise sources to be considered are RF fields emanating from on board
transmitters, precipitation static, induced lightning currents, and
induced noise from adjacent wiring.
2.1 Precipitation Static and Lightning Effects
Since precipitation static and lightning can occur only in the . atmos-
phere, and the CCTV system is not normally expected to operate during
launch and landing, these noise sources will not have any effect
on the video signal quality.
There may be concern that a lightning strike during launch could
damage the video circuits and hamper system operations in orbit.
Taking the worst case lightning induced magnetic field peak value
(1200 AMP/M) in the flight deck area from Reference 2, assuming a
30 ft wire length and 2 inches above the ground plane, and.applying
the induced voltage equation from Reference 2, Appendix H yields;
E.= (1200 AMP/M)(360 in.x 2in.)(405x10- 6 ) = 350 volts
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A conservative estimate of the shielding effectiveness for the multi-
point grounded shields on the video circuits is 20 db. This results
in a worst case common mode voltage on the video circuit of j5 volts.
The video circuits should be capable of tolerating a 35 volt transient
without sustaining damage.
2.2 Orbiter Transmitter Radiated Field
Orbiter transmitter radiated fields should not interfere with the CCTV
system operation since the -lowest transmitter frequency is 225 MHz-ATC
voice, and the TV system 3db bandwidth is specified as 1 Hz to 10 MHz
(See Reference 3).
2.3 Noise Coupling from Adjacent Circuit hiring
Analysis of noise coupling from associated circuit wiring to the video 	 f^,
signal circuits requires the evaluation of a number of variable
parameters. Specified-or measured values are assigned when they are
available. However, conservative assumptions are made where. significant
uncertainties are involved. This approach leads to results which tend to
be worst case. Table I gives values for parameters used in calculating
noise for each mode of coupling.
Inspection of the
sources of steady
-	 These signals are
RI has maintained
As a result video
connectors.
video signal wire -outing reveals that the primary
state coupled interference are other video signals.
given an EMC category of Class R and where practicable
the appropriate wire separation by EMC class.
signal wires are grouped together in bundles and
TABLE I _NOISE PARAMETERS VS. COUPLING MODES
1'/11% ''WI.ILRJ - I'I V19	 V1.3UM L'1 L' - Nr UrIM111LHL
AND RESULT-
	
NOISE VIDEO/VIDEO
	 'VIDEO/VIDEO' TRANSIENT SWITCH
ING NOISE	 COUPLING' COMMON	 'WIRE-TO- (COMMON TRANSIENT
VOLTAGE
	 MODE CONNECTOR	 'WIRE CONNECTOR) (COMMON
' CONNECTOR)
SOURCE IMPEDANCE-OHMS 75 75 _ 100 50
NOISE GENERATOR
LOAD IMPEDANCE-OHMS 75 75 25x103 50
NOISE GENERATOR
SOURCE IMPEDANCE-OHMS ' 75 106 75 75
NOISE RECEPTOR
LOAD IMPEDANCE-DBMS 75 106 75 75
NOISE RECEPTOR
FREQUENCY-HZ 107 107 105 107
LENGTH OF C014MON 0.333 17 0.333 0.333
ROUTING PATH.- FT
WIRE SEPARATION 0.103 0.25 0.19 0.19
DISTANCE - IN
HEIGHT ABOVE 0.25 2.0 0.25 0.25
GROUND PLANE - IN
CONDUCTOR 0.025 0.025 0.025 0.025
DIAMETER - IN
CONDUCTOR AND	 0.050	 0.050	 0.050	 0.050
INSULATOR
DIAMETER - IN
INSULATION
	 2.1	 2.1
	
2.1
	 2.1
DIELECTRIC CONSTANT
EFFECTIVE GENERATOR
	 1.0	 1.0	 28	 28
VOLTAGE - VOLTS
NOISE VOLTAGE ON
	
2.3	 602*	 0.4
	 149
RECEPTOR CIRCUIT -
MV. PEAK TO PEAK
* This value does not include the beneficial effects of shielding and
common mode rejection.
For the interim system configuration, connector J1/30P6 on the VIU
can have two video signal inputs (one from a flight deck camera and
one from a mid deck camera) and has one video signal output to the
S-Band Signal Processor. To predict the amount of video crosstalk
in the connector, noise frequency and amplitude must be determined.
Leading and trailing edges on the TV composite waveform contain the
highest frequency components. Examination of the waveform shown
in Figure 5.2.3.2.1-1 of Reference 3 reveals a maximum voltage excur-
sion of one volt and a specified maximum risetime of 0.3 microseconds.
Since Reference 3 specifies an upper limit (3 dB point) of the video
circuits of 10 MHz, it is assumed that the risetime could be as fast
as 0.1 microsecond. Therefore, a frequency of 10 MHz is used for
calculation of video crosstalk in connectors. For frequencies below
10 MHz, coupled noise decreases in linear proportion to the frequency.
Common connector crosstalk is also a function of the distance between
the pins carrying different video signals. Actual dimensions were
taken from Sheet A-5 of Reference 4 and are included in Table I along
with assumed values for all required parameters. The result obtained
is 2:3 millivolt peak to peak coupled from the Panel 019 (Flight
Deck) video signal to the video signal input for the S-Band FM Signal
Processor. This level is taken as typical for common connector cross-
talk.
There are nine video circuits in this connector for the operational
system. It is assumed that all nine video signals will be in phase
since all cameras will be drive by a master sync signal. Coupled
noise will then be in phase and algebraically additive, resulting
°;
a
in worst case peak to peak crosstalk of 18:4 millivolts (8 circuits
x 2.3 millivolts). This represents a peak to peak signal to peak
to peak noise ratio of 35 dB.
2.3.2 Common Connector Transient Noise
Connector 30P732 carries the video signal into Forward Avionics Bay
3 to the S-Band Signal Processor. Sharing this connector are 36
MDM 28 volt discretes and eight mechanically switched control functions.
The MDM discretes were characterized in Reference 5 with respect
to rise and fall times and load and source impedance. Rockwell has
estimated a maximum switching rate of 3/minute for MDM discretes.
Assuming a linear distribution from 0 to 3 discrete transitions per
minute, the typical rate for any one discrete would be 1.5/minute.
This result in an average transient rate on the video signal of 54
per minute. Table I gives the parameters used in calculating the
coupled transient amplitude. Dimensions for wire separation were
taken from Sheet A-11 of Reference 4 for the discrete in nearest
proximity to the video signal. A frequency of 100 KHz is used since
the MDM discrete have rise times>1Qgsec. The calculated coupled
transient is 0.4 millivolts.
The mechanically switched control functions have uncontrolled rise
and fall times. A conservative worst case noise frequency of 10 MHz
was therefore arbitrarily selected. The switching rate from these
functions is expected to be low. Since primary Bus power is applied
through the switches, an impedance of 50 ohms is assumed for source
and load. This is the nominal value measured by RI on SAIL Buses
yand documented in Reference 6. The calculated coupled transient 	 {
is 149 millivolts.
2.3.3 Common Wire Bundle Crosstalk
Calculations of crosstalk between video circuits routed together
in a common wire bundle is not straightforward since the degree of
unbalance (common mode rejection) is undefined. The approach used
assumes that the noise generator circuit is single-ended and the
noise couples common mode to the receptor circuit. This yields 0.602
volts of common mode noise at 10 MHz. A conservative estimate of
shielding effectiveness of the video circuit wiring is 20 dB for
the noise generator circuit and the same for the noise receptor circuit.
This will reduce the coupled common mode noise to 6.02 millivolts.
As many as nine video circuits have been found to have a common routing
path.for the operational system. • Since the operational system will
have all composite waveforms in phase, the crosstalk noise will add.
Eight circuits coupling to one circuit results in 48.2 millivolts.
The fact that the video circuits are balanced will reduce the crosstalk
noise in proportion to the square of the common mode rejection.
For example, a commmon mode rejection figure for all video circuits
of 20 dB will reduce the 48.2 millivolts to 0.482 millivolts and 40
dB will reduce to 0.00482 millivolts. Note that these values are
worst case for frequency, length of cable run, and number of synchro-
nized video circuits.
I
4 s• .. 6
if
3.0 CONCLUSIONS
The most signficant source of steady state interference is video
crosstalk in common connectors. Common connector crosstalk can be
as high as 2.3 millivolts for the interim system and 18.4 millivolts
for the operational system.
The most significant source of transient interference is common connector
coupling of mechanical switch functions. These transients can be
as high as 149 millivolts..
The significance of the predicted noise levels is not apparent since
allowable noise is undefined in the Communications and Tracking Require-
ments Definitions Document (SD72-SH-0105), or in EIA Standards RS170
and RS330. The EIA standards only define the video composite waveform.
4	 I	 l	 l_. s ^
4.0 RECOMMENDATIONS
Evaluation of pic
existing hardware
picture fidelity.
to newly designed
been performed on
predicted in this
titre quality degradation should be performed on
by injecting known noise levels while observing
The results of such a test should be applicable
equipment also. If similar noise level tests have
past programs, comparison of that data to the levels
paper would aid in evaluating present systems.
a
^	 ^	 3
5'0 REFERENCES
1. AFSC Design Handbook OH1-4, Electromagnetic Compatibility
2. Orbiter Electromagnetic Effects Compatibility Control Plan,
SD75-SH-02}+
3. Requirements-Definition Document, Communications and Tracking,
SD72-SH-0105
4. Connectors, Electrical, Circular, Miniature, High Density,
Environment Resisting, Specification For, 40M38277
5. MDTSCO Design Note 1.3-DN-CO204-019, Preliminary Orbiter Data Bus
Noise Prediction Study
6. Rockwell Internal Letter, 382-230-BLG'77-068, SAIL DC Power Bus
Measurements
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Orbiter CCTV video signal noise analysis

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