Westinghouse Type KR Installation & Operating Instructions Manual page 7

T YPE KR C A R RIER SET
0
Transmitter
1 . Disconnect the coaxial cable and replace with
a 50, 60 , or 70 ohm non-inductive resistor depending
on the characteristic impedance of the cable used .
2 . Fig. 9 sh ows typical output filter connections
for various frequency ran ges . In s ome cases it may
be necessary to use either a higher or lower range
to tune the filter ro resonance .
3 . Insert fuses F-1 and F-2 to apply power to
the apparatus .
4 . Connect an A-C
(VTVM) across the non-inductive load .
5 . Unblock the transmitter
1R
CARRIER TEST SWITC H .
jum per ttery positive to terminal 1 5 .
6 . Beginning with the output control R-42 at the
maximum counterclockwise
clockwise until a reqding appears on the VTV M .
Tune capacitor C - 1 9 for a maximum voltmeter reading.
7 . W-hile increasing R-42 , tune the output filter
for maximum output until the
resistor is approximately 8 volts. (Approximately
5 . 5 volts when operating from 48-volt station battery . )
8 . Open the test switch and reconnect the coaxial
cable.
Receiver
1 . The oscillator output control R-4 is pre-set at
the factory. However, shou ld any of the oscillator
and the crystal) R-4 will require
components be changed (including the transistors
a. C onnect an A-C VTVM to jacks
b. Adjust R-4 for a 0 .3 volt reading on the meter .
2 . The unit is shipped to have a gain of approxi­
mately 2 50 millivolts (to produce 10 rna relay current)
with input control R-1 in maximum clockwise posi­
tion . About 1 0-db additional gain or 80 millivolt
sensitivity can be obtained by clipping out resistor
Pos
R-74 , which is connected to the base of Q-4 and the
supply for the IF . A further 10-db gain or addi­
tional 25 millivolt sensitivity can be obtained by
also clipping out resistor R-73 , which is connected
to the base of Q- 5 and the Pos . s upply for the IF .
Resistors R-7 1 and R-72 have been se lected at the
factory to provide an overall gain of approximate ly
2 5 millivolts with R-73 and R-74 removed.
Vacuum Tube Voltmeter.
by closing the
An alternative is to
position , advance it
output across the
adjustment.
and
J-3 J-4.
a. Sensitivity A djustment for Noise
If the maximum o n-frequency noi se level is known
o r can be measured, the recei'{er can be adjusted for
this l eve]. Disconnect the coaxial cable and connect
a 60-ohm non-inductive resistor and a VTVM acro ss
terminals 1 1 and 12 . Energize the transmitter .and
output control R-42 for the same output as the max­
imum noise. Then adjust the receiver input control
R - 1 to obtain 1-m a output current. If it is impos sible
m
to obtain 1- a output current with control R- 1 in the
maximum clockwise positio n , then clip out resistor
R -74, which is connected to the base of Q-4. If the
gain is still insufficient, clip out resistor R-73,
which is connected to the base of Q-5. After com­
pletin g the adjustment of R- 1, restore the transmitter
to full output.
b. Sensitivity Adjustment for R emote Signal
When the maximum on-frequency noise is un ­
known and cannot be conveniently measured, the re­
ceiver may be adjusted for the remote signal .
determine the channel attenuation u sing a Sierra
vol tmeter or some other convenient method. Dis­
connect the coaxial cable and connect a 60-ohm
non-inductive resistor and a VTVM across terminals
1 1 and 12. Add 1 5-db to the channel attenuation.
This compensates for average vari ation s such as
channel and voltage variations. For example, if the
channel attenuation is 5-db, add thi s to the 1 5-db
makin g a total of 20-db. Taking this from 8 volts
output of the tran smitter , the receiver
be set for a sensiti vity of 0 . 8 volts. To do this, ad­
just the transmitter output control R - 42 for 0 . 8 volts
and then adjust the r eceiver input control so as to
tain lD-ma output
obtain 10-ma output current. If it is impossible to ob­
cur rent with control R- 1 in the
maximum clockwise position , clip out resistor R - 74 ,
which is connected to the base of Q-4. If the gain
is still insuf ficient, clip out r esistor
connected to t he base of
adjustment of R- 1, restore the transmitter to full
output.
It must be kept in mind that the two preceding
adjustment procedures are to be u sed as a guide and
will cover the majority of cases; however, cases m ay
arise where conditions change. For example, if the
adju stment is made per part a. , the noise m ay in­
crease due to various reasons such as bad insulators ,
which would require adjusting the receiver to be less
sen sitive. In the adjustment of part b ., the attenua­
tion m ay increase due to sleet or line switching ,
First
should then
Q-
which is
R-73,
5 . After completing the
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