GE LBI31072 Phoenix User manual

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PHOENIX*
MAIIIITENANGE MANUAT LBI3 TTI72
450470 MHz 20-WATT MOBILE COMBINATION
GEr{ERAL@ETECTRTC

SYSTEM SPECIFICATIONS .
COMBINATION NOMENCLATURE .
DESCRIPTION ...
LBr31072 TABLE OF CONTENTS
1ii
iv \/
1
OPERATION 2 ,'
INITIAL ADJUSTMENT
Transmi tter Adjustment
Receiver Adjustment
Re-Installation
CIRCUIT ANALYSIS
Transmitter.
Recei ver
Channel Gua rd
Power Distribution
MAINTENANCE ...
Disassembly ....
Driver & PA Transistor Replacement ...
Removing ICrs .
TEST AND TROUBLESHOOTING PROCEDURES
Service Techniques
Test Points .. ..
Transmitter Alignment Procedures
Receiver Alignment Procedures
Receiver Test Procedures
Receiver Audio and Squelch lltaveform Checks
OUTLINE DIAGRA.MS
2 ,\-
2--
2
,
z
6_
7'
o
10
10
11
12
72
12
12
15-16
L7
l8
l9
Transmitter/Recei
I n t ercon nec t /Osc iver Board ......
llator/Channel Guard Board 24
24
23
25-26
27 -29
30
30
3L-34
32
SERVICE SHEET
Hookswi tch . .
Externa I Speaker
SYSTEM INTERCONNECTION DIAGRAM
SCHEMATIC DIAGRAMS
Interconnect/Osci 11ator/Channel Guard Board
Transmitter/Receiver Board (Sheets 1, 2 &,3)
PARTS LIST
PRODUCTION CHANGES
ILLUSTRATIONS
1 - Transmitter/Receiver Block Diagran
2 - Power Distribution ..
3 - Q251 Lead Identification
4 - Mechanical Layout ....
5 - Test Equipnent Set Up
6 - Transmitter Troubleshootlng
7 - Receiver Troubleshooting
Figure
F i gure
Fi gure
Fi gure
Fi gure
Fi gure
Fi gure
J
o
11
L4
l6
2L
Although the highest DC voltage in this mobile equipment is supplied by the vehicle
battery, high currents may be dravrn under short circuit conditions. These currents can
possibly heat .metal objects such as tools, rings, watchbands, etc., enough to cause
burns. Be careful when working near energized circuits!
High-1eve1 RF energy in the transmitter Povrer Amplifier assembly can cause RF burns
upon contact. Keep away frorn these circuits when the transmitter is energizedl
11 Copyrignt @ tgBl cenerat Etectric Company

L8r31072
SYSTEM SPECIFICATIONSI
FCC IDENTIFICATION NUMBER
GF, IDENTIFICA?ION NUMBER
FFEQUENCY RANGE
Recei ver
Sque I ched
Unsque lched
Transmi tter
FREQUENCY STABILITY
TEi{PERATURE RANGE
DUTY CYCLE
DTMENSTONS, LESS ACCESSORTES (g X W X D)
WEIGHT, LESS ACCESSORIES
TRANSMI TTER
AXAgMZTRlO 1A
TR1O1A
450-470 I'IHz
250 milliamperes
650 milliamperes
5.5 Amperes @ 13.8 Volts
0.0005%
-30"C (*22"F) to +60oC (140"F)
2O% Transmit, 100% Receive
65 MM X 190 MM X 240 MM
(2.55 X 7.5 X 9.4 inches)
2.O7 kg (4.5 pounds)
POl{EB OUTPUT
CONDUCTED SPUFIOUS AND
HAR['ONIC EMISSIO}I
IiODLJLA T I ON
AUDIO SF.NSITIVITY
AUDIO FREQUENCY
CHARACTER]STICS
DI STORT I ON
DFVIATION SYi\4METRY
MAXIMTIII FREQUENCY
S PREAD
RF OUTPUT IMPEDANCE
20
-70
r4,5 kllz (+3.5 kHz volce
nodulation and 0.75 kHz
CG modulation )
65 to 72O Millivolts
at J91 1-4
3.5 to 6 M'i I I ivolts at
Within +1 dB to -3 dB of
a 6 dB per octave pre-
emphasis fron 300 to 3OO0 Hz
per EIA standards. Post
limiter filter per FCC and
Less thA! 3% (1000 Hz)
Less than 5% (300 to 3000 Hz)
0.5 kHz naximum
5.5 MHz
50 ohms
AUDIO OUTPUT (to 4.0
ohms speaker)
SI]NSITlVITY
12 dB SINAI)
20 dB Quieting
Method
SELECTI V I TY
EIA Two-Signal
Me t hod
SPURIOUS RESPONSE
INTERMODULAT I ON
MODULATION ACCEPTANCE
SQUELCH SENSITIVITY
FREQUENCY RESPONSE
RF ]NPUT IMPEDANCE
-85 dB @kHz
-85 dB
-75 dB
+7,O kEz
<8 dB SINAD
Within +2 and -8 dB of a
staodard 6 dB per octave
de-emphasis curve from
300 to 3000 Hz (1000 Hz
reference )
50 ohms
0.4
o .45
* These specifications are intended
appropriate Specifications Sheet pri.marily for use of the serviceman. Refer to the
for the complete specifications.

DESCRIPTION
Genera I Ill ect ri c Phoeni x mobi Ie combi-
na.tions are ful1y transistored -- utilizi-ng
L.,oth di screte components anci integrated
circujts (IC's) for high reliab'i1ity. The
rarJio i s a sel f-contained, FM transmitter/
recejver with built-in controls and speak-
er. Its sma I 1 size makes it idea-I for
fr:ont mounting in conventional vehicles.
The stanclarrl combinations are equipped with
the following:
o One receive frequencY, and two
transmi t frcquencies
o P1 ug- j n crYsta I s for +0 ' 0005%
oscil lator stabi litY
o Channel Gr-tard (tone squelch)
ll'he raclio consists of an effective
hea t-di ssipating, aluminum die cast rrHrr
frame on which two ci rcuit boards are
mountecl. The transmitter/receiver board is
mounted on the bottom of the "H" frame and
includes FF and receiver audio circuitry'
The Interconnect/Oscillator/Channel Guard
( IOC) board contai ns a 1 I interconnections,
oscillator circuits, transmitter audio pro-
cessor , mi crophone preampl ifier , and Chan-
ne1 Guard ci rcuitry. Al 1 externa.l connec-
tors, controls and indicators are mounted
c] irectl)'on the two boards for rellability
anC ease of di sassemblY.
\* The hoarcls plug into each other, elim-
i na ting the need for i nterconnecting wires.
The only wires used in the ra.dio are the
plug-jn leacls for the internal speaker.
The top anr! bottom covcrs enclose the rrHrr
frame ancl provide optimum protection for
the radio. The internal speaker mounts on
the jnside of the top cover"
The front control panel is made of
highly durable plastic wlth rounded corners
and recessed controls for passenger safety
requirements. The panel provides access to
four standard operator controls: a POWER
crn/Off pushbutton, a momentary MONITOR
pushbutton (fixecl squelch and Channel Guard
monitor), a rotary, an edge-mounted Volume
contr()1 , and a two-posi tion frequency se-
I ector (RpTR-DIR) . A red Transmit indi-
cator t.FD (Light Fmj tting Diode) and a
green power on indicator are provided'
No pou'er supply is required since the
highest supply voltage used in the radio js
providr.d by the vehicle battery. The radio
i s de.si gned for operation only in 12 Vo1t,
negative ground vehjcle systems.
The'radio is of modular construction.
Both major modules and tuning adjustments
are easi 1y accessiblt'. Loosening the two
screws i n thc' rea r of the top cover pro-
vides access to the inte'rconnect or multi-
frequency/interconnect board.
LI_) 1:i 10 7 2
cover provicles access to tLe transnri ltcr/
receiver board.
An optional set of test probes can be
plugged onto the test pins on the board for
alignment and troubleshootlng. Illea.sure-
ments can be made using GE Test Set 4EX3A11
or a mul-timeter,
TRANSil{ I TTER
The transmltter consists of an FM ex-
citer with an audio processor and a broad-
band, fixed-tuned power amplifier. The RF
power output level is pre-set lnternally to
rated power. Once the 1eve1 1s set, a
sensing control circuit holds it constant
as temperature and/or voltage vary within
specified limits.
Frequency stability for both the
transmitter and receiver is maintained by
an electronic compensati-on network.
RECE IVER
The dual conversion receiver consists
of a front end section and two mixer/IF
sections operating at 21.4 NlHz and 455 kHz.
The receiver also contains a squelch and
audio section. The audio section provides
a 3-watt audio output into a 4-ohrn load.
AC POV/ER SUPPLY OPTION
To use the radio as a base station, an
optional 121 Volt AC, 60 llerLz power supply
is available. An eight foot cable connects
the power supp)-y to the radio. The cable
length permits the power supply to be 1o-
cated away from the radio. A green Power
On LED is located on the front panel of the
power supply.
M ICROPFIONE
The standard mobile combinations use
an electret microphone, The mi-crophone is
housed in a sturdy case, and the extendable
coiled cord plugs into a jack at the back
of the radio. The microphone is secured to
the radio by means of a strain relief hook
on the microphone cabIe. A microphone
hanger is supplied with the rnicrophone.
HOOKSWITCII OPTION
1n Channel Guard appllcations, a
microphone hookswitch may be suppli.ed wi-th
the radio. The hookswitch is equipped with
a Channel Guard disable switch,
Placing the switch in the "up"
position (towards the smaIl speaker syrrbol)
dlsables the receive Channel Guard. Iti-th
the switch in the "down" position, the
Loosen i ng
the two screws in the rear of the bottom

LnT31072 DESCRIPT ION
Channe.l CrrarC is disabled when the
microphone js removed from the hookswitch.
EXTERNAL SPEAKER (OpTTONAL)
A five-inch speaker, contained in a
LFXANo housing, provides an audio output of
3 watts. The nomina I speaker impedance is
3.2 ohms. The speaker leads are connected
to pin-s 3 and 7 of Systems plug P910. IVhen
the Externa I Speaker is used, the jumper
from H13 to H14 on the (IOC) board can be
removed or P904 unplugged to disconnect the
hui I t-in speaker. A LEXANo bracket is sup-
p) j ed for moun t i ng.
OPERATION
Complete operating instructions for
the Two-lVay Radio are provided in a sepa-
rate Operatorts Manual. The basic proce-
dures for receiving and transmitting
messa ges fo 1 1 ows :
TC RECEIVE A }.4ESSAGE
1. Turn the radio on by pushing in
the POWER pushbutton.
2. Push in the I,{ONITOR button to dis-
able the squelch circuit and Chan-
nel Gua rd decoder. Adjust the
volume control for a comfortable
I istening level and then release
the I\{ONITOR but ton f or norma 1
operation.
The radjo is now ready to receive
messages from other radios in the system.
TO TFANSI4IT A I\,IESSAGE
'| Turn the radio on as clirected in
the "To Receive a lr,lessage" sec-
tion.
2. Press the PTT switch on the micro-
phone and speak across the face of
the nnicrophone jn a normal voice
level. Release the PTT switch as
soon a s t he messa ge ha s been
given. The red inriicator I ight on
the control panel will glovr eacb
tirne the microphone PTT switch is
pressed, inr!icating that the
transmitter is on the air. The
receiver is rnuted when the trans-
mitter is keyed.
INITIAL ADJUSTMENT
After the radio has been installed (as
described in the Installation I\4anual), the
following adjustments should be made by an
2
electronics technician who holds a Firsl or.
Second Class FCC Radiotelephone license
(where requi red ) .
TRANSTI I TTER ADJUSTIVIENT
Adjustments for the Lransmi tter in-
clude measuring the forward and reflected
power and adjusting the antenna length for
optimum VSIJR, then setting the transmitter
to rated power output. Next, measuring the
frequency and modulation and entering these
mea suremen t s on the FCC requi red sta t ion
records. For the complete transmitter ad-
justment, refer to the Alignment Procedure
(see Table of Contents).
RECEIVER ADJUSTMENT
The initial adjustment for the recei-
ver includes tuning the input circuit to
match the antenna. For the Receiver Ad-
justment Procedure, refer to the Alignment
Procedure (see Table of Contents).
CHANNEL GUARD DISABLE
All radios are equipped with Channel
Guard. 1n applications where Channel Guard
is not desired, disable the Channel Guard
circuit by connecting a jumper from J910-B
to J910-9. Also, remove the versatone if
present.
RE- INSTALLATION
If the mobile combinati.on is ever
moved to a different vehicle, always check
the battery potarity of the new system.
CIRCUIT ANALYSIS
TRANS}{I TTER
The transmitters utilize a crystal
control led, frequency modulated exciter for
two-frequency operation in the 4bO-4TO trtiHz
frequency band. The solid state transmit-
ter uses integrated circuits and discrete
components for increased reliability. The
transmitter consists of audio processor
U1O1; osci I 1a tor Q151, and Q15t, buffer
Q153, exciter stages e201 through e2O4; pA
ampl i fier Q251 through Q253, and power
control circuit q2S4 through e287. The
exciter provides approximately 150 milli-
wa t ts of modula ted RF to the pA which
provides rated output power. Figure 1 is a
block diagram of the radio showing both the
transmitter and receiver.
I\{ICROPHONE PREATIPLIFIER
A preamplifier stage (e901 and
associated circuitry) is provided for the

FF- 45o-47o MHz 2t.4 uxz
[c,
R ECE
--lI
k- so.o-*z.zzz MHz
AUDIO
-J
rx xrAL FREa. = F3
Rx xrAL FRE. = E#!I:
RCONNECT/OSC /CG
TR AIiST
MUTE GATE
- l5O,O - 1 56.566 MHz

LB13 1072
455 KHr .--l
R 521
AUDIO
LEVEL
VOL /SOUELCH HI
;EIVER
cERAt'llc
FILTER
(455KHd
2502
IF LIM /FM DET/
AUDIO PRE AMPL
u30?
e!!4 osctttaloRz
MIXER/IF AMPL
u 50r
FROM CHANNEL GUARD
A UDIO
MUTE
GATE
o 605
AUDIO
AMPL
u6 0l
SMI TTER
POWER CONTROT
0254- A257
Z HELICAT
RESO -
NATORS
t2t4,L2t5
45O - 47O MHz
RC4240
Figurel-BlockDiagram
sxclrEn e-L+ PwR. AMPL.

L8I31072 CIRCUIT ANALYSIS
standard electret microphone wi.thout a
built-in preamplifier. The preamplifier
circuit is located on the IOC board.
With this microphone, MIC HI is
coupled througb J911-5 to the preamplifier
stage. The ampl i fied output is coupled
through R908 and C905 to the audio pro-
cessor.
For optiona 1 microphones with a
bui I t-in preampl i fier, audio is coupled
through J977-4, bypassing MIC PRE AMp e901.
AUDIO PROCESSOR U1O1
The audio n"o".=.o. provides audio
pre-emphasis with amplitude limiting and
post limiter filtering. A total gain of
approximateTy 24 dB is realized through the
audio processor. 20 dB is provided by
U101B and, 4 dB by U101A.
The 8.5 Vol t regula tor powers the
audio processor and applies regulated +8.5V
through p9O3-2 to a voltage divider con-
sisting of R101, R111, R110 and R109. The
+4.25V output from the voltage divider
establishes the operating reference point
for both operational amplifiers. C1O6
provides an AC ground at the summing input
of both operational amplifiers.
Resistors R109, R110, R111 and diodes
D101 and D102 provide limiting for U101B.
Diodes D101 and D102 are reverse biased at
+7.7 VDC. Voltage divider network R109,
R110 and R111 provides +b.9 VDC at the
cathode of D101 and +2.6 VDC at the anode
of D102. The voltage at the junction of
D101 and D102 is 4.25 VDC. C104 and C108
permit a DC level change between U101B-z
and the voltage divider network for diode
biasing.
When the input signal to U101B-6 is of
a magnitude such that the amplifier output
at U1018-7 does not exceed 4 volts p-p, the
amplifier provides a nominal 20 dB gain.
Itfhen the audio signa 1 level at U101B-7
exceeds 4 volts PP, diodes D101 and D102
conduct on the positive and negative half
cycles providing 100% negative feedback to
reduce the amplifier gain to 1. This
limits the audio amplitude at U1018-Z to b
volts PP.
Resistors R105, R106 and R10? and ClOz
comprise the audio pre-emphasis network
that enhances the signal to noise ratio.
R107 and C1O7 control the pre-emphasis
curve below limiting. R106 and CLOT con-
trol the cut-off point for high frequency
pre-emphasis. As high frequencies are
attenuated, the gain of U101 is increased.
Audio from the preamplifier or
microphone is coupled to the input of
operational amplifier U101B-6. The
amplified output of U1018 is coupled
through R114, R7I2 , R104 and R11Z to a
second operational amplifier U101A.
The Channel Guard (CG) tone input is
applied to U101A-2. The CG tone is then
combined with the microphone audio.
A post limiter filter consisting of
U101A, R112-R114, C10B and C110 provides 12
dB per octave roll-off. R104 and C102 pro-
vide an additional 6 dB per octave roll-off
for a total of 18 dB.
The output of the post limiter filter
is coupled through C110 to the temperature
compensated transmitter oscillators Q151
and Q152.
TRANSMIT OSCILLATOR
A tempera ture compensa ting network
consi,sting of R151, R152, R1b3, R154, D1b1
and C151 maintains oscillator frequency
over a temperature range of -30o to +60.C.
The temperature compensating DC voltage and
audio is applied to FM modulator DIS2
through MOD ADJ control R155 and R1b9.
Modulator varactor D151 varies the transmit
frequency at the audio rate applied from
the audio processor.
Q151, Y1b1 and associated circuitry
comprise a Colpitts oscillator which g.ne:
rates the ninth subharmonic (50 MHz) oi the
RF carrier frequency. The transmit
osci I lator is adjusted to the assigned
operating frequency by L151. The oscil-
lator output is applied to buffer e153, and
is then coupled through p1b1 to the exciter
circuitry transmitter/receiver (Tx/Rx)
boa rd .
The second oscillator stage is
identical to the F1 oscillator. The
desired frequency is selected through Tx
frequency swi tch S1b1 and channel Common
switch Q154.
Q154 is normally turned on so that the
emitter of the selected oscillator is
grounded through S151 and Q1b4, tqrning the
selected oscillator on.
SERVlCE
R112-R114 are 7% resistors. This
tolerance must be maintained to
a ssure proper opera tion of the
post limiter filter. Use exact
replacements.

SERV I CE
Tbe channel common circuit is for
factory test PurPoses onlY. The
circui t permits both frequencies
to be checked regardless of the
posi tion of S151. The circuit
consists of Q154, Rt72 and C168.
Groundirg channel common lead
J911-6 turns off Q154 and Permits
each transmit oscillator to be
turnecl on by grounding P911-7(F1)
and then P911-8(F2 ).
CIRCUIT ANALYSIS L8r31072
EXCITER
The exciter consists of a 1.50 llHz
amplifier a (150 \llIz to 45O MHz) tripler
and two 450 I{Hz amplifiers. The exciter
takes the output from the osci I 1a tor and
buffer circuits (2 milliwatts minimum) and
multiplies and amplifies 1t to provide 140
milliwatts minimum (45O-47O I{Hz) to the
power amplifier circuitry. In addition to
these functions, the exciter contains aIl
of the filters whicb determine the band-
width and spurious characteristics (exclu-
sive of harmonics) of the transmitter'
The output of the osci I 1a tor and
buffer stages is coupled to the input of
the exciter via J151, which is connected to
a tap on L2O1. This tap also supplies
voltage to the buffer transistor Q153.
L201 along with L2O2, selects the third
harmonic (150 \!lHz) rvhich is present aL
J151.
C2O6 and C2O7 natch the output of thls
two pole filter to the base of Q201' which
provides approximately 10 dB of gain. C273
and C2l4 match the collector of this tran-
sistor to the input of another two pole
filter, consisting of L2O4 and L205. The
emitter voltage on LzOl (AMPL-1) can be
monitored at Tp201, and is typically +0.3
vcl ts.
C216 and C2I7 match the output of L205
to the base of the tripler transistor'
Q202. The base voltage on Q2O2 ean be read
at'lP2O2, and is t1'pically -1.2 vo1ts. The
tripler has approximately 3 dB of gain.
A matching network consisting of L206
and C222 matches the 450 MHz output of the
tripler to the first two-po1e helical fi1-
ter, L2O7 and L2O8. The output of this
filter is tben matched by C223 and L209 to
a two stage, broadbanded 450 [4Hz amplifier
consisting of Q203 and Q204 . C227 , C228 '
L210 and L211 provide proper matching from
the collector of Q203 to the base of Q2O4,
providing the necessary bandwidth as we11.
Although this amplifier is capable of pro-
viding 12-I5 dB of gain, both stages are
hiased to provide adequate saturation to
ensure no AM components are present at the
exciter output. Typical actual gain is 7-9
dB, and typical power output is 150 mW.
The collector of Q204 is matched to
the input of the second two pole helical
filter (L214 and L215) by C233-C235, L272
and L213. An RF "sniffing" circuiL con-
sisting of C236, C237, D2OI, and R221 allow
relative power available at the input of
this filter to be monitored at TP203. +0'6
volts is typically present at thj"s point
after tuning the exciter.
There is no test point that indicates
rela tive power coming out of this fil ter
TP251 in the PA sect.ion indicates relative
power coming out of Q251 (Amp1 4) , and
final tuning for L214 and L215 should be
done while monitoring this test point. No
test points require the use of special RF
detector probes.
POWER AMPLIFIER
The three stage power amplifier con-
sists of Amplifier Q251, driver q252 and
power ampl ifier Q253 and associated cir-
cuitry. Collector voltage for driver Q252
is applied from A+ through power control
transistor q257 and L256, L257 and R256.
The colleetor voltage for Q252 is a result
of the output power setLing and voltage
variations at any given time. The output
of driver q252 is coupled to the base of
Power Amplifier Q253 through an impedance
matching network consisting of W254, C292,
C267 , C268 and C269.
Collector voltage for Q253 is provided
frorn A+ through L267, L262 and R258.
The 20 watt output of the PA is con-
nected to the 1ow-pass filter by W256 and
then to antenna relay K601.
RF POWER ADJUST CIRCUIT
The output power adjust circuit al1ows
the transmitter to be set to rated output
power. The power adjustment is attained by
control ling the DC col lector voltage to
driver Q252 through pass transistor q257.
The pass tra nsistor i s control I ed by a
feedback loop consisting of Q254 through
Q256. The power is set by potenLiometer
R260.
SERVICE
There are 4 points in the exciter
which are approximatelY 50 ohrns.
W201, W2O4, W205 and W251 (which
interface the 2 helica I fi1 ters
to the other exciter circuitrY).
These points can conveniently be
used to monitor or inject signals
for troubleshooting and testing
using 50 ohm sources and termi-
nations.

L8r31072
A change in output power is sensed by
D252 causing the base voltage of q254 to
change accordingly. For example, if the
output power increases, the base of Q254
goes more positlve, causing it to increase
conduction which lowers its col lector volt-
age. Q254 controls Q255, therefore as Q254
increases conduction, Q255 decreases con-
duction. This raises the voltage applied
to the ba se of Q256. Tbe conduction of
Q256 Cecreases proportionally, lowering the
base voltage of pass transistor Q257. The
resulting decrease in conduction of Q257
lowers the col lector voltage of driver
q252, tberetry lowering the output power in
proport ion to the excessive power ori gin-
a1ly sensed by the base circuit of Q254.
RECE I VER
The receivers are dual conversion,
superheterodyne FI\'I receivers designed for
one-frequency operation in Ihe 42O-572 \lHz
frequency range. A regulated 8.5 volts is
used for all receiver stages except for the
audio PA IC, whjch operates from the A+
supply.
'The receiver has intermediate fre-
quencies of 21.4 liHz and 455 kHz. Adjacent
channel selectivity is obtained by using
two band-pass filters: a 21.4 MHz crystal
fi I ter and a 455 kHz ceramic fi 1 ter.
Al1 of the receiver circuitry except
the osci 1 1a tor is mounted on the
transmit ter/receiver (Tx/Rx) board. The
receiver consists of:
Receiver Front End
21 .4 MiHz 1st IF circuitry
1st and 2nd Oscillators
455 kHz 2nd IF circuitry with FM
Detector
Audio PA Circuitry
Squel ch Ci rcui t ry
RECE]VER FFONT ENI)
An RF signa 1 from the antenna is
conpled through antenna relay K601 and two
helical resonators (L401 and L4A2) to the
t'ase of RF amplifier Q401. The output of
Q401 is coupled through three more helical
resonators consisting of L4O5-L4O7 to the
gate of 1st Mixer Q402. The front end se-
lectivity is provided by the five helical
resona tors.
OSCILLATOR & IVIULTIPLIER
Q301 , Y301 a nd a ssocia ted ci rcui try
make up a Colpitts-oscillator. The
o
frequency is control led by a third mode
crystal operateci at one ninth of the
required injeetion frequency. Voltage-
variable capacitor D301, L301 and Y301 are
connected in series to provide compensati-on
capability. The compensation voltage used
to control the transmitter oscillators is
applied to D301 to maintain stability.
L301 is adjustable to set the oscillator
frequency. R301 is in parallel with Y301
to insure operation on the third overtone
of the crystal.
The output of Q301 is coupled through
C304 to the emitter of buffer Q302. The
output of Q302 is coupled through P301 to
two tuned circuits (L351 and L352) on the
Tx/Rx board. L351 and L352 are tuned to
the third barmonic of the oscillator fre-
quency which is applied to the base of
Q351. The output of tripler A351 is
coupled to the source input of mixer Q402
through helical resonators L354 and L355.
L354 and L355 are tuned to the operating
frequency minus 27.4 MHz which is the ninth
nultiple of the crystal frequency.
The DC leve1 of the osci 1 Iator /
multiplier chain can be monitored at TP351.
The meter reading at this point is typical-
ly 0.8 VDC. The RF frequency from the
oscillator/multiplier chain and input level
to the mixer can be measured at TP401. The
meter reading at TP401 is typically 0.5 to
1 volts as measured using the Rx RF Detec-
tor Probe.
1ST I{IXER
The 1st mixer uses a FET (Q402) as the
active device. The FET mixer provides a
high input impedance, high power gain and
an output relatively free of intermodula-
tion products).
In the mixer stage, RF from the front
end helical filter is applied to the gate
of the mixer. Injection voltage from the
multiplier stages is applied to the source
of the mixer. The 21.4 MHz mixer 1st lF
output signal is coupled frorn the drain of
Q402 through an impedance matching network
(L409 and C410-C413 ) to crysta 1 filter
2501.The highly-selective crystal filter
provides the first portion of the receiver
IF selectivity. The output of tLre filter
is coupled through impedance-matching net-
work L501 to the 1st IF amplifier.
IST & 2ND IF & DETECTOR STAGES
1st IF Amplifier e501 is dual-gate
I{OSFET. The crystal filter output is ap-
plied to Gate 1 of the amplifier, and the
ampli-fied signal is taken from the drain.
The biasing on Gate 2 and the drain load
determines the gain of the stage. The
CIRCUIT ANALYSIS

CIRCUIT ANALYSIS L8r31072
amplifier provides approximately 20 dP of
IF gain. The output of Q501 is coupled
through an impedance matching network
(L502) that matches the amplifier output to
the input of IC U501.
U501 and associated circuitry consists
of the 2nd oscillator, mixer and 2nd IF
amplifier. The crystal for the oscillator
is Y501, and the oscillator operates aI
20 "945 lllHz f or lovr side in ject ion of the
2nd IF (standard), or 21.855 MHz for high
side injection with (Structured Option FT)
for those radios determined to be operating
on a tweet frequency. This frequency is
mixed with the 21.4 MHz input. The output
of the mixer is lirni.ted by D501 and D502.
L503 is tuned for the 455 kHz 2nd lF fre-
quency.
The output of U501 is coupled through
ceramic filter Z5O2 wlnich provi.des the 455
kHz selectivity, and applied to U502. Test
Point TP501 is used in a ligning the recei-
ver, and can be used to check the output of
u501.
U502 and associated circuitry consists
of a 455 kHz limiter, a quadrature type FM
detector and an audio preampl i fier. L504
is the quadrature detector coil. Audio
Level potentiometer R521 is used to set the
audio output level to the audio amplifier.
AUDIO AND SQUELCH CIRCUITS
AudioAudio is applieC to the Channel Guard
tone reject filter through P903-3 and back
to the de-emphasis network through P9O3-7.
The audio passes through the de-emphasis
network (R633, C608 and C609 ) to Volume
Cont rol R634.
Audio arnplifier IC U601 drives the
speaker at the desired audio level (up to
three watts). The feedback loop containing
R637, R638 and C611 determines the ampli-
fiers closed loop plain. R636 and C613 pro-
vide the higb audio frequency rol 1-off
above 6 kHz.
The audio amplifier can be muted by a
DC voltage from the receiver mute gate
(Q605) which uses different logic inputs.
These inputs are 8.5 V Tx, MONITOR, or a
squelch signal. The Rx MUTE function from
the Channel Guard circuit which is applied
through P903-4.
Squel ch
Tbe squelch circui t operates on the
noise components contained in the FM
detector output. The output of U502 is
applied to frequency selective noise
arnplifier Q601 that has a resonant circuit
(L601, R604 and C6O2) as the col lector
1oad. The output is noise in a band around
7 k{z.
The noi se output i s coupled through
Squelch control R607 to expander ampllfier
Q602 which improves the level discrirnina-
tion characteristics of the circuit. The
output of Q602 is applied to a passive
voltage doubler circuit (D603 and D604).
This circui t has a high source impedance
and operates as an average value rectifier.
Fol lowing the vol tage doubler is a
Schmidt trigger (Q603-Q604 ) . The Schmidt
trigger provides the necessa ry hysteresis
and a we1 1-defined output signa I for Rx
IIUTE gate Q605
Wi th no RF signa 1 present, the
detected noise a t the vol tage doubler
output turns on Q603, turning off Q604.
This causes Q605 to turn on, applying +1.
volts to pin 2 of audio amplifier U601.
This voltage turns off U601 and mutes the
receiver.
When an RF signa I is received , the
noise at the output of Q601 decreases and
drive to e603 is removed. This turns off
Q603 and al1ows Q604 to turn on. With Q604
turned oD, Rx IVIUTE gate Q605 turns of f .
This turns on U601 so that audio i-s heard
at the speaker.
The squelch sensitivity is adjusted by
R607 in the base circuj.t of expander ampli-
fier Q602.
Pressing in the MONITOB pushbutton on
the front of the radio opens the Rx MUTE to
disable the Channel Guard. It also grounds
the base of Q601 and disables the squelch
function.
CHANNEL GUARD
Channel Gua rd is a continuous tone
encoder/decoder for operation on tone fre-
quencies in the 71.9 Hz to 210.7 Hz range.
The encoder provides tone-coded modulation
to the transmitter. The decoder operates
in conjunction with the receiver to inhlbit
all calls that are not tone coded wlth the
proper Channel Guard frequency.
The Channel Guard circui try consists
of discrete components for the Encode
disable, PTT switch, and receiver mute
switch; four thick-film integrated circuit
modules consisting of Decode Module U1001,
Encode Module U1002, Frequency Swi.tchable
Selective Amplifier (FSSA) U1003, plug-in
Versatone Network ZIOOI and monolytic IC
U1004 in the tone reject filter.
For a f uncti-ona I di.agram of the Chan-
nel Gua rd Encoder/Decoder , refer to the
troubleshooting procedures.
References to symbol numbers mentioned
in the fol lowi-ng text are found on the

Ltsr31072
Schema tic Diagram,
Parts List. Outline Diagram and
FSSA
Frequency Switchable Selective Ampli-
fier (FSSA) U1003 is a highly stable active
bandpass filter for the 71.9 Hz to 2I4.7 Hz
frequency range. The selectivity of the
filter is shifted across the bandpass
frequency range by swi tching Versatone
Networks in the fi I ter ci rcui t .
The gain of the FSSA is a function of
the tone frequercy. The Tone Frequency is
determjned by the Tone Network connected in
the FSSA circuit. Versatone Network 21001
is a precision resistor network.
ENCODE
V/hen PTT swi t ch i. s opera t ed , the Cha n*
ne I Gua rd encode t one i s genera ted by
coupling the output of FSSA bandpass filter
U1003 back to its input through a phase
inverting amplifier circuit and a limiter
circuit. The output of the FSSA is coupled
from U1003 to the input of the phase
inverting amplifier at U1002-9.
An amplifier provides 180o phase shift
of the tone frequency at the output. The
output of the phase inverting amplifier
circuit is coupled from U1002-6 to the
input of the limiter circuit at U1002-5.
A limiting network sets the tone out-
put coupled from U7402-4 to the input of
the FSSA (U1003-12) at 53 millivolts peak
to peak.
The limiter circuit is also used as an
encode switch. Keying the transmitter
applies +5.4 Volts to UlO02-2. This starts
the ci rcui t osci I 1a t i ng. Tbe tone frequen-
cy is determined by the tone network con-
nected in the FSSA circuit.
The tone output of the encoder circuit
is taken from U1002-7 and coupled through
tone output ampl i fier Q1002 and modula t ion
adjustment 81010 to the audio processor on
the transmi tter/receiver board.
DECODE
Aud i o from Vol ume/Squel ch high tha t
contains the correct frequency is coupled
to pin 1 of Decode Module U1001. Pin 1 of
U1001 is the input of an act ive, three
stage, low pass filter. The low pass fil-
ter attenuates frequencies over 21O.7 Hz.
The output of the 1ow pass fi lter at
U1001-15 is applied to U1001-14. U1001-14
is the input of a limiter circui t, limiting
CIRCUIT ANALYSIS
the output at
peak to peak. U1001-13 Lo 55 millivolts
The output from the limiter is coupled
to Pin 12 of FSSA U1003. Since the tone is
the proper frequency, the FSSA will a1low
it to pass. The output of the FSSA is
coupled to U1001-3. U1001-3 is the input
to an amplifier circuit. The output of the
amplifier at U1001-4 is coupled to the in-
put of a threshold detector at U1001-6.
In the mute mode, when the tone decod-
er in U1001 detects the Channel Guard fre-
quency, Q1005 turns Q1006 off. This un-
mutes the receiver audio. In the squelch
mode, Q1006 is operating, grounding the Rx
MUTE lead and muting the receiver audio.
Audio from VOL/SQ HI is applied to the
tone reject filter. The tone reject filter
is an active filter consisting of U1004 and
associated circuitry. A11 frequencies from
7O to 210.7 Hz are rejected by the fj.Iter,
while passing all other audio frequencies
back to the recei'rer audio circuits (fil-
tered VOL/SQ HI ).
Encode Disable
The Encode Di.sabIe circuit consists of
Q1003 and Q1004. To disabte the encode
circuit, a positive voltage (+8.b to 14
VDC) is applj.ed to Molex connector p910-b
at the rear of the radio. This is accom-
plt"!gO by temporarily jumperins pgto-9 (CG
DISABLE) to p910-11 (A+). Thls positlve
voltage is applied to the base of e1003,
turning on both Q1003 and e1004.
STANDARD TONE FREQUENCIES (Hz)
77.9
7 4.4
77 .O
79 .7
82.5
85.4
88 .5
91 .5
94.8
97.4
100 .0
103.5
707.2
110.9
114.8
118.8
123.0
t27 .3
131.8
136.5
141 .3
146.2
151 .4
756.7
203.5
270.7
162
I67
t73
179
186
192
2
o
8
o
2
8
SERVICE
The Encode Disable circuit has
been incorporated as a maj-nten-
a nce a id for the servi ceman .
This circuit disables the Channel
Guard encode cireuit and allows
the serviceman to make transrnit-
ter distortion and modulation
checks without removing the cover
from the radio.

\{hen turned oD, Q1004 app1ies +B'5 VDC to
the base of PTT Switch Q1001, forcing it
off. With Q1001 off, the operating voltage
for the encocler IC U1002 and Encode Tone
Output Stage transistor Q1002 is removed,
preventing any tone output.
POWER DISTRIBUTION
The battery voltage (A+) connects to
the radio through J910-1 and J910-11 at the
rea r system connector to the IOC boa rd.
Both lnputs are connected to reverse polar-
ity protection diodes D901 and D9O2. The
ground lead is coupled through the same
connector and is connected to chassis
ground through a fusable printed wi ring run
which will open if the ground wire is acci-
dently connected to A+ (see Figure 2).
INTERCONNECT/OSC / CG BOARD
CIRCUIT ANALYSIS
PWR ON INOICATOR
M lC PRE A[4P
One battery input goes directly from
the IOC boa rd through a feed-through
capacitor in FL9OT to the lransmitter PA
stages. The other input feeds through
P903-6 to the main board for two functions'
One branch for the audio amplifier passes
through an RC-rippte flller (R642 and C619)
and one of the sections of POWER On/Off
switch S602. The other section of lhe
POWER On/Off switch controls the A+ to
voltage regulator U602. The regulator
output is fixed at 8.5 volts by means ol
selected resistor R640. Refer to the
Receiver Schematic Diagram for resistor
selection instructions.
Regulated 8.5 volts i-s switched to
either the receiver or the Lransmitter and
Tx indica tor by the antenna relay ' The
antenna relay is also powered by the 8.5
volt regulated supply. The non-latching
relay is operated by the PTT switch on the
microphone, completing the path to A-.
The squelch circuit, the audio proces-
sor and parls of the IF amplifler U502 are
supplied directly from the continuous 8.5
volt supply.
The receiver front-end, the receiver
oscillator, the 21.4 MHz IF stages and the
second oscillator are supplied from 8.5 V
Rx. The transmitter oscillator and the
exciter are supplied from 8.5 V Tx.
TRANSMIT/RECEIVE EOARD
LBIU1072
EATTERY (+}
tcNrTtor 5w
(OPTIOMLI
BATTERY (-}
MIC ROPHONE
M IC ROPHONE
PTT
I
CAUTION
When usinpr the Encode Disable ci r-
cuit, do rot remove the microPhone
f rom t he opt i ona t hookswi t ch ( i f
present) or place the monitor switch
on the hookswitch in the "uP" posi-
tion. In station aPPlications, do
not place the CG MON Switch on the
desk microphone in [{ON Position.
This will short the supply voltage to
ground, resulting in possible damage
to the equipment.
ON
RECEIVER CKTS
TRANSMITTER CKTS
TRANSMIT INOICAIOR
AUDIO PROCESSOR
I
TX OSC CKTS
Figure 2 - Power Distribution

LBr37072
MAINTENANCE
PREVENTIVB I{A INTENANCE
To insure- bigh operating efficiency and to prevent mechanical and electrical fail"ures
from interrrlpting system operations, routine checks should be made of all mechanical and
electrlcal parts at regular intervals, This preventive maintenance should include the
checks as listed in the table of Maintenance Checks.
DI SA SS EI4BLY
To service the transmi tler/
receiver (Tx-Rx) board, loosen the
tvzo screws securing the bottom
cover at the rear of the radio.
Then sl ide the cover out from
under tbe edge of the front
control panel and lift off.
To service the IOC board, loosen
the two screws at the rear of the
radio and sl ide the cover out from
the edge of the front control
panel and lift off .
To remove the Tx-Rx board:
Remove the top and bottom
covers.
Remove the four screws securing
the front panel to the ,,H,r
frame a nd remove the front
panel.
MAINTENANCE CHECKS lNTERVAL
o
Mon t hs AS
Requi red
CONNECTIONS - Ground connections and connections to the voltage source
should be periodically checked for tightness. Loose or poor connec-
tions to the power source will cause excessive voltage drops and faulty
operation. When ground connections are not made directly to the bat-
tery, the connection from the battery to vehicle chassis must be
checked for low impedance. A high impedance may cause excessive volt-
age drops and alternator noise problems.
x
ELECTPTCAL sYsrEM - check the voltage regulator and alternator or gen-
erator periodically to keep the electrical system within safe and
economical operating limits. over-voltage is indicated when the bat-
tery loses water rapidly. usage of 1 or 2 ounces of water per ce1l per
week is acceptable for batteries in continuous operation. A weak bal-
tery will often cause excessive noise or faulty operation.
X
I4ECHANICAL INSPECTION - Since mobile
shock a nd vi bra t i on , check for 1 oose
to mal<e sure that nothing is working units are subject to constant
p1ugs, nuts, screws and parts
I oose .
x
ANTENNA - The antenna, antenna base and
clean and free from dirt or corrosion.
should become coated or poorly grounded,
signal will result.
all contacts should be kept
If the antennas or its base
loss of radiation and a weak
X
ALIGNMENT - The transmitter and receiver meter readings should be
checked periodically, and the alignment "touched up" when necessary.
Refer to the applicable ALIGNI{ENT PROCEDURE and troubleshooting sheet
for typica I voltage readings.
x
FREQUENCY CHECK
quired hy FCC. - Check transmitter frequency and deviation as re-
Normally, these ehecks are made when the unit is first
put into operation, after the first six months and once a year there-
after.
x
Be careful when removi.ng the
top cover as the speaker
leads are connected to the
boa rd .
10

I{A I NTENANCE
Remove the eight screws secur-
ing the RF shield.
Unsolder the antenna connector
and remove the trto retaining
screws.
Remove the two screws in the PA
transistor Q253.
Turn the radio over and remove
the hex screw Post, washer and
copper spacer from the stud of
Driver transistor Q252.
Remove the 9 sc rews securi ng
the Tx-Rx board and carefullY
lift up the board off of the
i nt erconnec t i ons Pi ns .
To remove the interconnect/
mul t i-frequency boa rd ;
Remove tbe toP cover.
In multi-frequency units, t€-
move the five screws securing
the RF shield.
Remove the 12 screws securing
the board and carefullY lift
the board up to disconnect the
interconrection pins.
PA TRANSISTOR REPLACEMENT
LBr:i1072
printed circuit board runs because
part of the matching network is
included in the base and collecLor
runs.
Tri-m the new translstor leads (if
required) lo the lead length of
the removed transi stor. The
1et Ler rrcrr on the top of the
transistor a lso indicates the
col lector (see Figure 3 for
t ransistor lead identifica tion ) .
Apply a coa t of si 1 icon grea se
between the mounting surfaces of
the spacer and to both sides of
the insulator of Q252 and between
the mounting surfaces of Q253 and
the heat sink and on both ends of
the spacer. Place the transistor
in the mounting hole. Align the
leads as shown on the Outline
Diagrarn. Then hold the body of
the transistor and replace the
transistor mounting hardware,
using modera te torque of 0.6
Newton meters (Nm) or 6 inch
pounds) for M2.5 screw size and
1.0 Nm (8 inch pounds) for the hex
screw post. A torque wrench must
be used for this adjustment since
transistor damage can result if
too little or too much torque 1s
used.
Solder the leads to the printed
circuit pattern. Start al the
inner edge of mounting hold and
solder the remaining length of
transistor lead to the board. Use
care not to use excessive heat
that causes the printed wire board
runs to Iift up from the board.
Check for shorts and solder
bridges.
7. Replace Tx/Rx board and reassemble
radio.
REMOVING }C ! S
Removing ICrs (and a1I other
soldered-in components) can be easily
accomplished by using a de-soldering tool
such as a SOLDA PULLTo or equivalent. To
remove an IC, heat each lead separately on
the solder side and remove the old solder
with the de-soldering tool.
5.
4.
7.
t
J.
I]RIVER -AND b.
Q253: To replace PA RF transistors Q252 and
1 . Rernove Tx/Rx boa rd .
2. Unsolder one lead at a time with a
50 watt soldering iron. Use a
scribe or X-actroo knife to hold
the lead away from the Printed
circuit board until the solder
cool s.
Lift out the transistor, and re-
move the old solder from the
printed circuit board with a de-
sol deri ng tool such a s a SOLDA
PULLTo. Special care should be
taken to prevent damage to the
WARNING
The stud mounted RF Power Transis-
tors used in the transmitter contain
Beryllium Oxide, a TOXIC substance.
If the ceramic or other encaPsula-
tion is opened, crushed, broken or
abraded, the dust may be hazardous
i f inha led . Use care in rePlacing
transistors of this tYPe. CAUTION
Failure to solder the transistor
leads as directed may result in
the generation of RF loops that
could damage the transistor or
may cause low power output.
11

L8r31072 MAINTENANCE
o252 025 r
NARROW LEAD
IS COLLECTOR NARROW LEAD
IS COLLECTOR
M2. 5 XB---=-
SC REW S
RC4?75
.t
I'I
Figure 3 - Q251
An a I ternate method is to use a
special soldering tip that heats ali of the
pins simul taneously.
TEST AND TROUBLESHOOTING PROCEDURES
Maintenance of radio is facilitated by
use of the Troubleshooting Charts and
servicing techniques unique to this radio.
The Troubleshoot ing Chart is designed to
lead you rapidly to the defective component
or circuit. Typical voltage readings are
provided on the Schematie Diagram for your
reference when troubleshooting.
Troubleshooting charts are provided
for most major prob'lems that might arise in
the Transmi tter/Receiver section of the
radio.
SFRVIClNG TECHNIQUES
The high cl.ensi ty plug-in desigr of the
modular radio lends itself well to rapid
jsolation of rpalfunctions in the voltage
and signal paths. A majority of the
Lead Identification
signals and voltages pass through the
connectors on the IOC board.
To isolate a signal or voltage path to
determine loading effects, loca te short
circuits, ete. carefully insert an insulat-
or (plastic wand, toothpick) between the
appropriate pins of the related Molex con-
nector to create an open circuit. Signals
paths that may be isolated include: Volume
SQ HI, filtered volume squelch HI, PTT, Rx
II{UTE , a nd SPKR HI .
TEST POINTS
RF Detector probes for the recei-ver
section are available for alignment pur-
poses and to monitor the lst receiver
injection at TP401 and the 2nd IF at TP501.
An RF signal probe also is available to
monitor the transmitter frequency.
Seven test points are provided al
eritical circuit locations to monitor
operation.
They are as follows:
TRANSI',f ITTER
Tp201 Al{pL 1 (Q201) Emitter Voltage
'TP2O2 TRIPLER (Q202) Base Voltage
TP203 AMPL 3 (Q204) Relative Output
TP251 AI{PL 4 (Q251 ) Rela t i ve Out put
RECEIVER
TP351 Tripler Output - Q351
TP401 Receiver 1st oscitlator injection
TP501 455 kHz IF
12

MAINTENANCE LB131,O72
CAUT ION
Before bench testing the radio
bench power supply. be sure of the output voltage characteristlcs of your
To protect the transmitter power output transistors from possible instant destructi-on,
the following input voltages must not be exceeded:
Transrnitter unkeyed: 20 Volts
Transmitter keyed (50 ohm resistive load): 18 Volts
Transmitter keyed (no load or non-resistive, load): 15.5 Volts
These voltages are specified at the normal vehicle battery terminals of the radio and
take the voltage drop of standard cables into account. The voltage limits shown for a
non-optimum load is for "worst case" conditions. For antenna mismatches 1ikely to be
encountered in practice, the actual limit wiIl approach the 18 VoIt figure.
iir
ri
il'
Routine transmitter tests should be performed at EIA Standard Test Voltages (13
for loads of 0 to 6 amperes: Input voltages must not exceed the limits shown VDC
even
for transient peaks of short duration.
Many commonly used bench power supplies cannot meet these requirements for load
regulation and transient voltage suppression. Bench supplies which employ "brute
force" regulation and filtering may be usable when operated in parallel with a 12 Volt
automotive storage battery.
GENEFAL ELECTRIC COMPANY. MOBILE COMMUNICATIONS DIVISION
WORLo HEAOOUARTERS. LYNCHBURG. VIRGINIA 24502 U.S.A.
r,t .
'/ui,:
GEN ERA L@ ELEOTRIC
fradema.k ol General E lectric CompanV U.S.A
PrintedinUSA. 13

LBI3 LO72
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,s,\,*, s, SCOPE
S]-]TT ] \ G\'tRT TC rT 2 VOLTS/tr
MOD
i \OTE: -{\ RIIS OR PEAK
RLADI\C YOLT ]IETER IYTI,I,
RLTD I i2 TO L,/3 OF PEAK-
TO_PL{K RL1DI\GS.
AUDIO SE\S1T1\-IT"I'
1, Connect audio oscill.ator output across Jgli-{
just outpur for 1OO0 Hz at 1.0 I|RMS.
2, Reduce generator output until deviation iai-
less than 120 Eillivolts.
OEGREES FAHRE\-:
ADJUST
Rt0t0
FT
FREO
ADJUST
Ll51
Fl MOD
ADJUST
R155
F2 TX
FREO
ADJUST
Lt52
75.2 7A I 5:;
F2 MOD
ADJUST
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