Rockwell international Collins 980N-1 User manual

"
-
.,
523-0759341-002111
2nd Edition, 15 May 1978
Rockwell
International
instruction book
Collins 980N-1
Altimeter Test Set
Collins Air Transport Division
Avion,cs and Missiles Group
Rockwell International
Cedar Rapids, Iowa 52406
..
Printed in the United States of America

1.1 PURPOSE OF INSTRUCTION BOOK
This instruction book provides information
necessary to install, operate, and maintain the
980N-1 Altimeter Test Set.
1.2 PURPOSE OF EQUIPMENT
The 980N-1 Altimeter Test Set (figure 1-1, CPN 522-
4610-001) is used primarily to isolate faults in the AL-
101 or AL-101A Radio Altimeter System and to per-
form routine flight-line maintenance tests
on the
system, while
it is installed in the aircraft. It also has
limited capabilities for operationally bench-testing
the 860F-1 Radio Altimeter and 339H-1( ) Radio
Altitude Indicator.
The
980N-1 Altimeter Test Set (figure 1-1, CPN 522-
4610-001 with SB 4, and CPN 522-4610-003), in addi-
tion to the above, provides a varying altitude
rate
signal to the radio altimeter system necessary to test
the Ground Proximity Warning System (GPWS), and
provides automatic descent rates for autoland tests.
1.3 EQUIPMENT COVERED
Table 1-1 lists the equipment covered by this instruc-
tion book.
section 1
general description
1.4 EQUIPMENT REQUIRED BUT NOT
SUPPLIED
The 980N-1 requires no additional special equipment
for testing the AL-101 or AL-101A systems. However,
a locally fabricated
test adapter is recommended to
perform
test procedures on the 980N-1. (See table 7-1,
and figures 7-21 through 7-23 for details.)
1.5 EQUIPMENT SPECIFICATIONS
Table 1-2 lists the specifications for the 980N-1
Altimeter Test Set.
1.6 PHYSICAL ][)ESCRIPTION
1.6.1 Mechanical Description
The 980N-1 Altimeter Test Set (figure 1-2) is a por-
table, unpressurized
unit enclosed in a 2-piece,
drawn-aluminum case. The top cover
is hinged and
detachable. Operating controls and indicators are
mounted on the
front panel, which is attached to the
bottom section
b:{ six screws. A cable assembly, ter-
minated in a
mating connector, provides connections
to the
980N-1 from the 860F-1 front panel connector,
J9. Provisions for mounting the 339H-1( ) indicator
on the front panel include the mating connector and
Table 1-1. Equipment Covered.
EQUIPMENT
DESCRIPTION
COLLINS
PART NUMBER
980N-1 Altimeter
AL-101 or AL-101A Radio Altimeter System Test. Set. 522-4610-001
Test Set
(Serno 351 and below)
980N-1 Altimeter
Functionally equivalent as CPN 522-4610-001 (serno 522-4610-001
Test Set 351 and below) and includes COM/ARM switch.
(Serno 352 and above)
980N-1 Altimeter Functionally equIvalent as CPN 522-4610-001 (serno
522-4610-003
Test Set 352 and above) and includes COM/ARM switch and
varying altitude rate signal generator.
Revised 15 May 1978
1-1

CHARACTERISTICS
Sensitivity
(for full-scale
deflection)
Trip accuracy
Vswr measurement
Accuracy
Duty cycle
Strapping options
Operating position
Revised 15 May 1978
section 1
general description
Table 1-2 Equipment Specifications (Cont)
SPE CIFI CA TIONS
High: ±1.2 V dc
Medium: ±6 V dc
Low: ±30 V dc
±2% of output voltage, or ±2.ft, whichever is greater
±10%
CPN 522-4610-001:
Continuous up to 1-hr maximum (limitation due to increased power
requirements on 860F-1 power supply)
CPN 522-4610-003:
Continuous up to 30-min maximum (limitation due to increased power
requirements on 860F-1 power supply)
CPN 522-4610-001 (serno 351 and below):
Either +27 V dc or ground connected to Alp warn arm or trip
common terminals
CPN 522-4610-001 (serno 352 and above) and CPN 522-4610-003:
Provide COMI ARM switch for selecting +27 V dc or ground for Alp
WARN and TRIP lamps
Upright and reasonably level
1-3

L
2.1 UNPACKING AND EQUIPMENT INSPEC-
TION
Remove all packing material, and carefully
remove the 980N-1 Altimeter Test Set from
shipping carton. Carefully inspect for possible
shipping damage. If damage exists, return unit
to shipping carton along with all packing mater-
ial and file damage claim with transportation
agency. If no damage exists, retain carton for
equipment storage purposes.
2.2 CONNECTIONS
For flight-line maintenance or bench perform-
ance testing, connect the 980N-1 cable assembly
to the 860F-1 front panel connector.
3.1 GENERAL
The 980N-1 provides a simulated altitude signal to the
860F-1 by means of a voltage-controlled oscillator
with a frequency range from
600 Hz to 130 kHz. A null
detector (meter) and followup potentiometer
are used
to measure
the 860F-1 precision output voltages. A
rate generator assembly (SB
4, and CPN 522-4610-
003) provides one of eight manually selected initial
altitudes (500, 800, 1100, 1400, 1700, 2000, 2300, and
2600 ft), and one of eight manually selected descent or
slew rates (500, 1000, 2000, 3000, 4000, 5000, 6000, and
7000 ft/min) used for checking the slewing action of
the GPWS and
the 860F-1. Indicator lamps provide a
visual check of
the 860F-l altitude trips, autopilot
warn contacts, flag voltage, and 339H-l( ) flag and
MDA trip operation. In addition, the 980N-l includes
a grounding switch for self-testing the
AL-I0l
system, plus a means'of checking the vswr ofboth the
reteive and transmit antenna cables. A built-in, self-
Revised
15 May 1978
section 2
installa tion
For 339H-l( ) testing, connect the unit to the
860F-1 front panel connector. remove the indi-
cator recess cover, mate the connector attached
to the recess cover with the 339H-l() rear
connector, place the 339H-l( ) into the recess,
and secure the unit to the 980N-l front panel
as shown in figure 4-1.
The 339H-2 does
not fit in the 980N-l; there-
fore, all indicator readings
must be taken on
the installed indicators in the cockpit.
In multisystem installations,
it is important
that only the system under test be energized
for certain tests.
section 3
operation
test feature checks the operation of the 980N-1. The
980N-l receives all
operating power from the 860F-1.
In most AL-I0l Radio Altimeter System install-
ations, the 339H-l( ) Radio Altitude Indicator
and 860F-l Radio Altimeter are remotely loca-
ted.
For this reason, provisions are included
for mounting the 339H-l( ) on the 980N-l front
panel as shown in figure 4-1. This eliminates
the need for frequent trips between the aircraft
radio rack and the cockpit control panel. It
also provides a convenient means of isolating a
malfunction to either the 339H-l( ) or the as-
sociated wiring. For example, if the 339H-l( )
indications do not agree with those on the
980N-1, the malfunction is known to be in the
339H-l(); if the 339H-l() operates properly
in the 980N-l but does not when installed in the
aircraft control panel, the malfunction is known
2-1/3-1

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Table 3-1. Postinstallation Testing and Troubleshooting Procedures Using the 980N-l Altimeter Test Set
(1) To zero meter:
(2) TRIP lamp operation:
(3) MDA lamp operation:
(4) AlP WARN and
A/PNOWARN
lamp operation:
(5) Self-test altitudes:
(6) 339H-2 indicators:
(7) 980N-l test set operation:
[Notes
Always begin with METER SENS switch in LOW position. To measure the 860F-l altitude output voltage, adjust the
ALTITUDE control to the desired input frequency (or
the desired operating point as in step 10), then adjust the
ALTITUDE STANDARD to zero the meter (pointer on midscale mark) with the METER SENS switch first
in LOW,
then MED (for increased accuracy), then HIGH (for best accuracy). To test the system at some specific input
frequency,
adjust the ALTITUDE STANDARD to the desired altitude as indicated by the digital readout, then adjust
the ALTITUDE control to zero the meter with the METER SENS first in LOW, then MED, and finally in HIGH
position.
When the TRIP lamp is lit,
this indicates that the trip contacts corresponding to the ALTITUDE TRIP SELECT
switch position are closed. If A5CR67 has been removed from the 860F-1, the TRIP lamp will not operate in
AL-I0l SELF TEST regardless of the ALTITUDE TRIP SELECT switch position. Refer to the applicable section
in the AL-101 or AL-I01A Radio Altimeter Maintenance Manual for additional information. The COMI ARM
switch (Sl1) on the 980N-l (CPN 522-4610-001, serno 352 and above, and CPN 522-4610-003) must be set to the
proper position (+27 or
GND) for TRIP lamp operation.
When the
MDA lamp is lit, this indicates that a closed circuit exists between the 339H-l( ) MDA or the 339H-2
DH
trip output terminals. An internal ground is provided in 980N-l SELF TEST to light the lamp. For all other
tests except VSWR, the
MDA lamp indication is dependent on the 339H-l( ) MDA or 339H-2 DH index position with
respect to the pointer
or reference. (The MDA lamp is not energized in VSWR test.)
The
AlP WARN and AlP NO WARN iamps are never lit simultaneously except in 980N-l SELF TEST. Otherwise,
the AlP NO WARN lamp is lit (and the AlP WARN lamp is out) for all simulated altitudes below 2500 feet. Above
2500 teet and in AL-lOl or AL-IOIA self-test, both lamp conditions are reversed. A reversed condition below 2500
feet indicates a warn condition in the 860F-1. The COMI ARM switch (Sl1) on the 980N-l (CPN 522-4610-001,
serno 352 and above, and CPN 522-4610-003) must be set to the proper position (+27 or GND) for AlP WARN
and AlP NO WARN lamp operation.
The altitude indication obtained
in AL-101 SELF TEST is dependent on the type of 860F-l used in the system. Refer
to figure
4A, in the AL-101 Radio Altimeter System Maintenance Manual (or figure 4 in the AL-I01A Radio Altimeter
System Maintenance Manual) for specific information.
Reference to 339H-l( ) indicators also includes 339H-2, unless noted otherwise.
a. 980N-l test set (CPN 522-4610-001, serno 352 and above, and CPN 522-4610-003) contains a COMI ARM switch
that connects the TRIP and AlP WARN lamps to ground or +27 V dc, depending on the altimeter system
under test. This switch must
be set to the proper position for TRIP, AlP WARN, and AlP NO WARN
lamp operation, and to GND for 980N-l SELF TEST operation.
b. 980N-l test set (CPN 522-4610-001 with SB 4 and CPN 522-4610-003) contains MODE, ALTITUDE, ALTITUDE
100 FEET, and RATE 1000 FT/MIN switches for altitude slew operation. The MODE switch must be set to
the MAN position for manual test set operation.
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Table 3-1. Postinstallation Testing and Troubleshooting Procedures Using the 980N-J Altimeter Test Set (Cont)
APPLICABLE 980N-I SWITCH
TEST TITLE, REMARKS, AND OR OPERATING CONTROL APPLICABLE 980N-I APPLICABLE 339H-I( )
SPECIAL INSTRUCTIONS POSITIONS INDICATIONS INDICATIONS
Auxiliary altitude output
TEST SELECT: AUX/IND Digital readout:
Flag out of view;
test at 480 feet. ALTITUDE;
0470 to 0490
COMI ARM: GND or +27
(Refer to note (7)a.) FLAG lamp: lit; ~DA lamp (if used):
MODE: MAN
refer to note(3);
(Refer to note (7)b.)
AIDIALT SELECT: 480FT(
);
MDA lamp: refer
Pointer: 480 feet.
ALTITUDE STANDARD: zero
meter; and refer to note (1). to
note (3).
Auxiliary
altitude output test TEST SELECT: AUX/IND 339H-2 DH CONT:
at selected altitudes. ALTITUDE; Index on
300 ft.
COM I ARM: GND or +27
(Refer to note (7)a.) All indicate same
MODE: MAN
altitude as digital
(Refer to note (7)b.) readouts.
AIDIALT SELECT: Flag
out of view.
VARIABLE;
ALTITUDE STANDARD:
600
MDA lamp; refer to
ALTITUDE control: zero note
(3).
meter, and refer to note (1).
For 339H-2:
Digital readout;
For 339H-2:
ALTITUDE control:
001; 0291 to 0309.
Adjust ccw until 001;
MDA lamp on, DH Others, 0346 to 0354
lamp on.
005; 485 to 515 006;
Others, audio tone.
400 ft, DH on, off
006; Adjust cw then ccw. readout:
010 to 015.
ALTITUDE STANDARD:
zero meter.
Autopilot
altitude output test
TEST SELECT: AlP
Digital readout:
Flag out ofview;
at 480 feet. ALTITUDE
AND TRIPS;
0470 to 0490
COM I ARM:GND or +27 FLAG lamp: lit;
MDA lamp (if used):
(Refer to note (7)a.)
MODE: MAN
refer to note (3);
AlP NO WARN
(Refer to note (7)b.) lamp: lit; Pointer: 480 feet.
AIDIALT SELECT: 480FT( );
ALTITUDE STANDARD: zero
MDA lamp: refer
meter, and refer to note (1). to note
(3).
MOST PROBABLE
CAUSE
OF
ABNORMAL
INDICATION
860F-Ior
339H-I( ) as
applicable
860F-Ior
339H-I( ) or
339H-2 as
applicable.
860F-I if step 6
result was cor-
rect, 339H-I( )
if pointer indica-
tion and digital
readout do not
agree
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Table 3-1. Postinstallation Testing and Troubleshooting Procedures Using the 980N-1 Altimeter Test Set (Cont)
APPLICABLE 980N-1 SWITCH
TEST TITLE. REMARKS.
AND
OR OPERATING CONTROL APPLICABLE 980N-1 APPLICABLE 339H-1( )
SPECIAL INSTRUCTIONS INDICATIONS INDICATIONS
POSITIONS
Altitude trip operating
ALTITUDE TRIP SELECT: 1;
Digital readout: Pointer: indicates
point check. indicates
trip no. 1 same
altitude as
ALTITUDE (control): adjust; operating point. digital readout on
980N-1.
ALTITUDE STANDARD:
adjust to zero meter.
ALTITUDE
TRIP SELECT: 2;
Digital readout:
indicates trip no. 2
ALTITUDE (control):
adjust;
operating point.
ALTITUDE STANDARD:
adjust to zero meter.
ALTITUDE
TRIP SELECT: 5;
Digital readout:
indicates
trip no. 5
ALTITUDE (control):
adjust;
operating point.
ALTITUDE STANDARD:
adjust to zero meter.
ALTITUDE TRIP SELECT: 6;
Digital readout:
indicates trip no. 6
ALTITUDE (control): adjust; operating point.
ALTITUDE STANDARD:
adjust to zero meter.
ALTITUDE TRIP SELECT: 7;
Digital readout:
indicates
trip no. 7
ALTITUDE (control): adjust; operating point'"
ALTITUDE STANDARD:
adjust to zero meter.
ALTITUDE
TRIP SELECT: 8;
Digital readout:
indicates trip no. 8
ALTITUDE (control):
adjust;
operating point.
ALTITUDE STANDARD:
adjust to zero meter.
MOST PROBABLE
CAUSE
OF
ABNORMAL
INDICATION
860F-10r
339H-1( ) as
applicable
--
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Table 3-1. Postinstallation Testing and Troubleshooting Procedures Using the 980N-J Altimeter Test Set (Cont)
TEST TITLE, REMARKS, AND APPLICABLE 980N-l SWITCH APPLICABLE 980N-l APPLICABLE 339H-l( )
SPECIAL INSTRUCTIONS
OR OPERATINGCONTROL INDICATIONS INDICATIONS
POSITIONS
VSWR
test - meter
TEST SELECT: VSWR; Meter (pointer):
00
Not applicable
calibration" RCVR-SET-XMTR: SET;
SET 00 : adjust for 00
indication on vswr scale.
VSWR test -receive TEST SELECT: VSWR; Refer to introduction,
antenna cable.
step 11.
RCVR-SET-XMTR: RCVR
(hold).
Flex cable slightly. Meter (pointer):
indication should
not change.
VSWR test - transmit
TEST SELECT: VSWR; Refer to introduction,
antenna cable.
step 11.
RCVR-SET-XMTR: XMTR
(hold).
Flex cable slightly. Meter (pointer):
indication should
not change.
--
Rf leakage of 860F-1. TEST SELECT: VSWR; A vswr indication
(Make accurate vswr of 1.7 or greater
measurement before RCVR-SET-XMTR:
XMTR
indicates excessive
leakage measurement.) (hold). leakage.
Replace one
antenna
with a load (Narda NORMAL/LEAKAGE:
757-20 Attenuator or LEAKAGE.
equivalent).
_._--
~--
('
MOST PROBABLE
CAUSE OF
ABNORMAL
INDICATION
Not applicable
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4.1 FUNCTIONAL DESCRIPTION OF 980N-l
OPERATING CONTROLS AND INDICATORS
4.1.1 General
This paragraph contains a functional description of
each operating control and test indicator used
on the
I
980N-1. (Refer to figures 4-1 through 4-3*.) This infor-
mation, together with the block diagrams (figures
7-5
through 7-30), provides the operator with sufficient
knowledge of the principles of
980N-1 operation to
form a logical conclusion as to the most probable
cause of an abnormal indication obtained during AL-
101 system or 980N-1 testing/troubleshooting. The
block diagrams show all switch terminal connections
for each TEST SELECT switch position.
4.1.2 ALTITUDE STANDARD Device
The ALTITUDE STANDARD is a digital readout
device with an associated precision potentiometer.
The +30-volt
de output from the 860F-1 is applied
section 4
principles of operation
across this potentiometer. The voltage at the wiper is
applied directly 1;0 one side of the meter circuit. The
altitude output voltage from the 860F-1 (either aux-
iliary or autopilot, depending
on the TEST SELECT
switch position) is applied to the other side of the
meter circuit through the METER SENS switch. Any
unbalance in the two voltages causes the meter to
deflect from the 0 position. When the ALTITUDE
STANDARD is adjusted so that the meter indicates 0
(or midscale), l:he digital readout indicates the
altitude (in feet) corresponding to the altitude output
voltage.
4.1.3 Meter
The meter used in the 980N-1 contains a single
pointer movement with two scales. One scale
is used
in
adjusting the ALTITUDE STANDARD as
described in paragraph 4.1.2. The other scale is used
to measure the
VBwr on the antenna cables. The move-
ment is very sensitive and for
that reason is protected
by diodes against high currents.
980N-1 (CPN 522-4610-001, Serno 351 and Below) Operating ControL~ and Indicators
Figure 4-1
(*) Figure 4-1 also shows the 339H-1( ) indicator installed in the 980N-1 front panel.
Revised
15 May 1978
4-1
I

4.1.4 METER SENS Switch
The METER SENS switch connects different values
of resistance in series with the meter movement. The
largest value of resistance is connected when the
switch
is in the LOW position, with lesser amounts in
the
MED and HIGH positions.
4.1.5 AIDjALT SELECT Switch
The AIDI ALT SELECT switch functions only when
the TEST SELECT switch
is in either the AUX/IND
ALTITUDE or
AlP ALTITUDE AND TRIPS posi-
Ition, and the MODE switch (SB 4 and CPN 522-4610-
003) is set to the MAN position. With the AIDI ALT
SELECT switch in the 480FT range (either 20, 40, or
57), a precision frequency is generated by a crystal-
controlled oscillator. This frequency represents an
altitude of
480 feet. With the AIDI ALT SELECT
switch in the VARIABLE position, the vco (voltage-
controlled oscillator) generates the altitude frequency
and
is adjusted by the ALTITUDE control. (Refer to
paragraph 4.1.7 for additional information on the
vco.)
4.1.6 ALTITUDE Control
The ALTITUDE control is a potentiometer that
varies the voltage applied to the vco. The internally
generated +30 volts dc
is the reference source for the
ALTITUDE control.
4.1.7 Frequency Generators
The 980N-1 contains two frequency generators, a
crystal-controlled oscillator, and a voltage-controlled
Ioscillator, used to provide the altitude signal to the
system under test.
The crystal-controlled oscillator generates one of
three frequencies depending on the AIDI ALT
SELECT switch position (19.885 kHz, 20.285 kHz, or
20.625 kHz). These frequencies represent 480 feet in
altitude for 20-,40-, or 57-foot AID values, respective-
ly. The output from the crystal-controlled oscillator is
applied to the 860F-1 only when the
AIDI ALT
I,
SELECT switch is in the 480FT range, and the MODE
switch (SB 4 and CPN 522-4610-003) is set to the MAN
position.
The voltage-controlled oscillator generates frequen-
cies from
600 Hz (approximately -20 feet) to 130 kHz
(approximately
3000 feet). The frequency is controlled
by the ALTITUDE control and
is applied to the 860F-
1 when the AIDI ALT SELECT switch is in the
Revised
15 May 1978
section 4
principles
of operation
VARIABLE position, and the MODE switch (SB 41
and CPN 522-4610-003) is set to the MAN position.
4.1.8 TRIP SELECT Switch and TRIP Lamp
4.1.8.1 980N-1 C.PN 522-4610-001, Serno 351 and
Below
I
The TRIP lamp and amplifier circuit is energized by
the +30 V
dc internally generated from the 26- V ac
input. The voltage
is applied only when the TEST
SELECT switch is in the 980N-1 SELF TEST, AL-101
SELF TEST, or AlP ALTITUDE AND TRIPS posi-
tion, and the MODE switch (SB
4) is set to the MAN I
position. The amplifier circuit is essentially an on-off
switch for the lamp and is used to isolate the
trip relay
contacts from the lamp current. The specific
trip to be
tested is selected by the ALTITUDE TRIP SELECT
switch. When the 860F-1 trip relay contacts
(associated with the
trip being tested) close, the trip
amplifier circuit enables the
trip lamp switching
transistor, causing the lamp to light. Special strap-
ping
is required and depends on whether the trip com-
mon terminal
is at ground or +27 V dc. If A5CR67 has
been removed from the 860F-1 being tested, the TRIP
lamp will not operate in AL-101 SELF TEST for any
ALTITUDE TRIP SELECT switch position.
The TRIP lamp
is always lit when the TEST SELECT
switch is in the 980N-1 SELF TEST position,
regardless of the position of the ALTITUDE TRIP
SELECT switch.
4.1.8.2 980N-1 CPN 522-4610-001, Serno 352 and
Above, and CPN 522-4610-003
The TRIP lamp is energized by the +30 Vdc internal-
ly generated from the 26- V ac input. The voltage is
applied only when the TEST SELECT switch is in the
980N-1 SELF TEST, AL-101- SELF TEST, or AlP
ALTITUDE AND TRIPS position, and the MODE
switch (SB 4, and CPN 522-4610-003) is set to the
MAN position. The specific trip to be tested is selected
by the ALTITUDE TRIP SELECT switch. When the
860F-1 trip relay contacts (associated with the trip be-
ing tested) close, the lamp lights. The COMI
ARM
switch selects GND or +27, depending on whether the
trip common terminal is at ground or +27 V dc. If
A5CR67 has been removed from the 860F-1 being
tested, the TRIP lamp will not operate in
AL-101
SELF TEST or any ALTITUDE TRIP SELECT
switch position.
The TRIP lamp is always lit when the TEST SELECT
switch is in the 980N-1 SELF TEST position,
4-3

virtually any type of failure or warn condition in
the 860F-l.
4.1.12 SET co Control and RCVR-SET-XMTR
Switch
With the TEST SELECT switch in the VSWR
position and the RCVR-SET-XMTR switch in the
normal-released (SET) position, the SET co
c'ontrol is used to calibrate the meter in prepara-
tion for a vswr test. In addition, with the TEST
SELECT
switch in the VSWR position, the AL-IOI
system is in self-test, since a ground is applied
to self-test terminals J9-j and PIB-24. To
individually
test the vswr on the transmit and
receive antenna cables, the bias current through
circulators ZI and Z2 is controlled as follows:
a.
With the RCVR-SET-XMTR switch held in
the XMTR position, +27 volts dc is applied to
the normally negative side of the transmit
circulator ZI, thus blocking current flow
through the circulator bias coil. Bias current,
however, is maintained through receive cir-
culator Z2. In this condition, the transmitted
signal is applied directly to the transmit an-
tenna cable as in normal (other than self-test)
operation. A signal (vswr) is reflected back
through the transmit circulator, self-test
delay line, receive circulator, and into the
receiver circuits. The tracking filter output
resulting from this signal is used in the 980N-l
as the transmit vswr test signal. If the vswr
is correct, a meter indication of 1.7 should be
obtained.
b. With the RCVR-SET-XMTR switch in the
RCVR position, the +27-volt dc blocking volt-
age is removed
and the receive circulator bias
coil is shorted. In this condition, the trans-
mitted signal is coupled from the transmitter
output directly into the self-test delay line,
bypassing the transmit antenna as is normal
for self-test. From the delay line, the signal
is coupled through the receive circulator to the
receive antenna (no bias current in this circu-
lator). The
signal from the receive antenna
cable (vswr) is then reflected back through
the receive circulator and into the receiver
circuits.
Revised
15 May 1978
section 4
principles
of operation
The introduction to the vswr tests, step 11 on
table 3-1, adequately describes the results that
should be obtained, as well as outlining the
probable cause of an abnormal result. The vswr
tuning stubs in the 860F-l are factory adjusted
to provide a VS\H of 1.7:1. Any deviation from
this value, in either direction, reflects degrada-
tion. The signal resulting from this vswr is
used in the 860F'-1 vswr monitor circuit. Any
vswr less than 1.4 results in a signal too low in
amplitude to permit satisfactory monitoring.
(860F-l equipment with SB 22 installed may not in-I
dicate the lower 101 vswr limit. Refer to 980N-l SB 3.)
An
intermittent poor vswr can occasionally be
detected by flexing
the cable slightly during test. Any
meter movement, while the cable is being flexed, can-
not be tolerated.
Cable-connector installation instructions
are con-
tained in the removal/installation section of the AL-
101 Radio Altimeter Maintenance Manual.
4.1.13 .'VORMAL LEAKAGE Su·itch
This switch is added as a customer option
when Service Bulletin No 1 is installed. This
modification is applicable to all 980N-l Alti-
meter Test Sets.
Rf leakage in the AL-I0l Radio Altimeter Sys-
tem can be det~ded by measuring the voltage
at test jack J21 in the 860F-l Radio Altimeter
while it is installed and operating. However,
this requires removing the dust cover from the
860F-1.
This modification incorporates a leakage
test
function into the 980N-l test set. Rf leakage
can now be detected by connecting the 980N-l
test set to the 860F-l front panel connector
J9-C. With this modification, rf leakage can
be detected witbout removing the 860F-l
dust
cover.
4.1.14 COM/ARM Switch
The COMIARM toggle switch (CPN 522-4610-001, ser-
no 352
and above, and CPN 522-4610-003) connects the
TRIP and AlP WARN lamps to ground or +27 V dc,
dependent on the
altimeter system under test.
4-5