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U17 and
U18
and the Total PEAK MOD thumbwheel form a precls10n positive
and negative reference for the modulation peak comparators U20.
RS3 and R86
provide reference for the 100% PEAKS PER MINUTE comparators.
Composite signal
from the A4 assembly
is
also fed to these comparators.
The outputs of these comparators are fed to one shots of
2
to
4
seconds
in the case of PEAK MOD and 5 milliseconds in the case of the 100% PEAKS PER
MINUTE.
The 100% PPM one shot drives a counter made up
U22. U23 and U24.
This counter is reset every minute by a pulse derived from the A3 assembly.
Composi
signal is also fed through the TOTAL METER POS and NEG
hes to the total meter driver circuit. U13, U14 and associated circuitry.
3. A3 (Dual Average Voltmeter)
ly
This board contains two identical voltmeter circuits, one for Channel
A
Display, one for Channel B Di
lay plus the reset generator (U10) and decoder
driver (Ul1. U12, U13) for the 100% PEAKS PER MINUTE display.
Channel A designators are in units; Channel B designators are in hundreds.
Al and U1 along with their associated PEAK thumbwheel are used
drive the
TEST DISPLAY PEAK led.
Signal components selected
by
the DISPLAY SELECT pus
buttons and the METER +J- switch are amplified or inverted by U2 and fed to a
combination attenuator-amplifier.
This combina on provi
gain in lOdB
steps from 0 dB to 50 dB.
The action is as follows:
RANGE
AMP
OdB
-30dB
+30dB
-lOdB
-20dS
+30dB
-20dB
-lOdB
+30dB
-30dB
OdB
+30dB
-40dB
-lOdB
+50dB
-50dB
OdB
+50dB
The range changes are accomplished by the outputs of up-down counter
U6 being used to clamp the appropriate resistors to ground through U3.
A
sample of the attenuator-amplifier output is fed to comparator
US. The
output of U8 in conjunction with gates U5, U6, and U7 then drives U6 up or
down to the required ran
The output of the attenuator-ampli
r is then peak detected
by
Q7
and
meter driver U9.
Q9 is used to change ballistics from FCC to
VU
as
required.
4.
A4 (Receiver) Assembly
Q1 and associated circuitry buffer and filter the output of the 1st
L.O. (fc
+
lO.7MHz).
This signal and the incoming RF are mixed in balanced
,~
'---.
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