Westinghouse Type KR Installation & Operating Instructions Manual page 48

mately 250 millivolts (to produce 10 rna relay current)
with input control R-1 in maximum clockwise posi­
tio!l. About 10-db additi onal gain or 80 millivolt
sensitivity can be obtained by clipping out resistor
R-7 4 , which is connected to the b ase of Q-4 and the
B+ supply for the IF. Approximately 10-db gain or
25 millivolt sensitivity can be obt ained by clipping
out resi stor R-7 3 , which is connected to the base of
Q-5 and the B+ supply for the IF. Resistor R-7 1 has
been se lected at the factory to provide an overall
gain of approximately 25 millivolts.
a. Sensitivity Adjustm ent for Noise
If th e maximum on-frequ ency noi se l evel is known
or can b e measured, the receiver can be adjusted for
thi s l evel . Disconnect the coaxial cabl e and connect
a 6Q-ohm non-indu ctive resi stor and a VTVM acros s
termi n al s 1 1 and 1 2 . Energize the transmitter and
output control R- 4 2 for the same output as the max­
imum noi s e . Then adjust the receiver input control
R- 1 to obtain 1-ma output current. If it is impos sibl e
to obtain 1-ma output current with control R- 1 in the
maximum clock wise position , then clip out resi stor
R-74, whi ch is connected to the base of Q- 4. If the
gain is stil l insu ffici ent , clip out resi stor R- 7 3,
which is connected to the base of Q-5 . Aft er c om­
pl eting th e adjustment of R- 1 , restore the tran smitter
to ful l output.
b. Sensitivity Adjustment for Remote Signal
When the maximum on-frequency noi se is un ­
k nown and cannot be conveniently measured, the re­
ceiver may be adjusted for the remote si gn al .
determine the channel attenuation u sing
vol tmeter or some other convenient method. Dis­
connect the coaxial cab! e and connect a 6Q-ohm
non-inductive resi stor and a VTVM across terminal s
1 1 and 1 2. Add 15-db to the channel attenuation.
Thi s compensates for average vari ations such as
channel and voltage variations. For examp l e, if the
channel attenuation is 5-db, add thi s to the 1 5-db
making a total of 2Q-db. Tak ing this from 8 volts
output of th e transmitter, the receiver
b e set for a sensiti vi ty of 0 . 8 vol ts. To do thi s, a(}
just th e transmitter output control R- 4 2 for 0 . 8 volts
and th en adjust th e r ecei ver input control so as to
obtain 1Q-ma output current. If it is impossibl e to ob­
tain 1Q-ma output cur rent with control R- 1 in the
maximum clockwise position , cli p out resi stor R- 74 ,
which is connected to the base of Q- 4. If the gain
is still insuf ficient, clip out r esistor R- 73, which i s
connected t o t he base o f Q- 5 . After compl eting the
8
adjustment of R- 1 . restore the transmitter to ful l
output.
It must be k ept in mind that the two preceding
adjustment procedures are to b e u sed as a guide and
will cover the majority of c ases; however, cases may
ari se where conditions change. For example, if the
adjustment is made per part a
crease due to various reasons such as bad insulators ,
which would require adjusting the receiver to b e less
sensitive. In the adjustment of part b., the attenua­
tion may increase due to sleet or line switching,
which would n eces sitate increasing the sensitivity of
the receiver.
Due to different type s of operation and supply
voltages, it is not practical to hav e a calibrated dial
for this unit. H owever, calibration may b e made at
installation by recording transmitter output ( either in
db or volts) at various knob s ettings of th e sleet
detector unit. Then , by adjusting the sleet detector
so as to obtain 10 milliamperes relay current at a re­
mote receiver, any increase or decrease in line at­
tenu ation may be noted as the difference between the
original s etting, and the setting required to obtain the
given 10 milliamperes.
With the appar atus energized , adjust R - 4 in the
250-volt resi stor unit so as to obtai n 1 25-volts at
terminal s 1 7 (B-) and 19 ( B + ) on th e rei aying set.
First
a Sierra
If th e frequency i s changed in the fi eld, i t i s
necessar y t o change th e i nput fil ter FL- 1 t o the de­
sired channel frequency. This fil ter is of th e
in type and may be r emoved by unsnapping the cl amp
and pull ing the f il ter out. The tran smitter
crystal Y- 2 must be changed to the desired channel
frequency . The receiver oscil l ator crystal Y- 1 must
be changed to the desired channel frequency plus 20
shou l d then kc. Fi gure 9
mitter output fi lter. It i s necessary to unsol der the
exi sting connections and make the new conn ections
per the chart. After compl eting t he
tuning procedure as described under Adjustments for
transmitter and receiver should then b e fol l owed.
Note als o that capacitors C2 and C9 in the
transmitter and receiver crystal oscillator circuits ,
respectively,
the noise may in­
. •
Sleet Detector
25Q-Volt Resistor Unit
Frequ ency Change
shows the connection s for th e trans­
p receding, the
may have t o b e changed.
plug­
oscil l ator
For fre-