Westinghouse Type KR, Installation & Operating Instructions Manual

Page: 84 / 124

order to m atch other switchboard equipment. The out­
line dim ensions and also the drilling plan for flush
and projection mounting are shown by Fig. 1. The
m ajority of the p arts are m ounted on a printed circuit
board. This board may be readily removed as follows:
1. Remove the two output plugs from the red and
black j acks.
2. Disconnect the receiver input coaxial cable
connector.
3.
Loosen the two screws at the top of the board.
4. Loosen the two screws at the bottom of the
board and pull them out as far as they will extend.
5. Pull board down to disengage the terminal s
and lift out.
The transmitter output filter may be removed by
removing four mounting screws from the bottom of the
case and disconnecting the coaxial cable.
Fig. 4 shows the location of major components
such as potentiometers, j acks, test p oints, crystals,
transistors, etc. External connections and the
Schematic Diagram are shown by Fig. 2. The
numbered terminals shown as squares apply to the
external terminals.
Provisions are made for plugging the Voice
Adapter Unit in the front or the rear of the relaying
e quipment. When front mounting is utilized, it will be
necessary to remove the cover of the KR case before
plugging in the Adapter Unit. In the case of rear
mounting, the Adapter Unit may be plugged into the
relaying equipment directly without
removal of
the
cover. Octal sockets m ark ed X-3 and X-4 (the latter
for rear mounting) on the relaying equipment accom­
modate the adapter plug. A buckle type strap on each
side of the adapter holds the unit in place after it has
been plugged in. The normal projection for a front or
rear m ounted Voice Adapter i s 3-inches beyond that
of the relaying equipm ent. When the KR Relaying Unit
is supplied for rear mounting of the adapter, a p atch
cord is available on separate order. This p atch cord
plugs into the t el ephone j acks on the adapter and pro­
vides an ext ension to a conveniently located terminal
board. The Wiring Diagram for rear mounting of the
adapter is shown in Fig.
3.
The p anel cutout information necessary for
mounting the Sleet Detector is shown by Fig. 9 . This
unit consists of a potentiometer and pushbutton
switch mounted on a small panel, itself suitable for
switchboard mounting.
4
For 258-volt operation, separate auxiliary resis­
tors are required.
E l ectrical
Transmitter
The tran smitter is made of four main stages in­
cluding an o scillator, driver, power amplifier, and an
output filter. In the o scillator, the crystal is operated
as a resonant circuit between the collector of one
transistor and the base of the other. The feedback i s
supplied through a capacitor from the collector of the
second transistor to the b ase of the first transistor.
The frequency is independent of voltage or tempera­
ture changes of the transistors. Thus the frequency
stability is the stability of the crystal .
The input to the driver stage Q- 10 is controlled
by potentiometer, R-4 2 which also controls the trans­
mitter power output. In H ZM relaying CARRIER STOP
provides about +40 volts for blocking. This is ap­
plied to Q- 10 through T-6. Diode CR-5 prevents damage
to the transistor when this positive voltage is ap­
plied to the collector. For CARRIER START ( when
in the blocked po sition) a small positive voltage is
applied to the collector of Q- 10 by means of bleeder
resistors R-67 and R-68 .
The power amplifier consists of two transistors
Q- 1 2 and Q- 15, which are operated as class B ampli­
fiers in push-pull. Resistors R-5 2 and R-55 are for
stabilization.
The output transformer, T-7 , m atches coaxial
cables of 50 to 70 ohm s.
Resistor R-66 tends to k eep the source
impedance
constant to p ermit p roper tuning of the output filter.
The output filter consists of coils L- 1 and L-2,
capacitors C- 19 through C-22. The filter is tunabl e,
and i s provided to att-muate harmonics and other
spurious outputs. It should be noted that the filter
contains no shunt elem ent s , resulting in a reverse
impedance free of "acro ss the line" resonances.
Receiver
The receiver is a superheterodyne in order to
obtain constant selectivity regardless of the channel
frequency. (See Fig. 1 1. ) The major stages include
an input filter, attenuator, oscillator, mixer, IF filters,
IF amplifiers, detector and a D-C power output stage.
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