i. CARRIER SHIFT Meter M2. Meter M2 is a
c. If Amplifier V2. The if amplifier rejects
zero-center meter that indicates the amount of
undesired output frequencies of the mixer and
carrier shift caused by the modulation of the rf
provides primary amplification at the 12 MHz
signal. Readings are in kiloHertz (kHz).
intermediate frequency which is fed to integrated
j. Divider Network. This precision divider is
circuit U 1.
used to select the amount of signal required for
d. If Amplifier and Limiter U1. The if amplifier
full-scale readings on the DEVIATION meter, as
and limiter possesses very high gain and a self-
set by the DEVIATION RANGE-KC switch. The
limiting capability at moderate input signal
levels. It has the ability to accommodate a wide
signal is then fed to the audio amplifiers.
range of input signal level, and eliminates the
need for automatic volume control (avc) elsewhere
coupled stages with cathode follower input and
in the circuit.
outputs. The band-pass is flat up to 70,000 Hertz
e. Limiters V7 and V8. Two cascaded limiter
(Hz). The output is fed to the DEVIATION meter
and the AUDIO OUTPUT binding posts.
further limiting of the if signal. They are broad-
l. DEVIATION Meter M3. This three-scale,
band tuned and the output of V8 is fed to the
five-range meter indicates deviation of fm signal
driver amplifier circuit.
f. LIMITING Meter M1. The LIMITING meter
is fed from the second limiter stage. When the
meter pointer is in the back range, it indicates that
accomplished by a bridge rectifier consisting of
the level of the rf input is sufficient for proper
CR8 through CR11. It has an unregulated 240-
operation of the modulation meter.
volt dc output. A regulated 195-volt dc output is
obtained by the use of voltage regulator stage
g. Driver Amplifier V9. The driver amplifier
V17, direct current (de) amplifier stage V16, and a
amplifies the limited if signal to the level required
series regulator stage V15. Ballast tube V14
for optimum discriminator operation.
provides a regulated filament voltage for use with
h. Discriminator T9. The discriminator con-
oscillator V1 and audio output cathode follower
verts the frequency-modulated if signal to
V13. Zener diode CR12 provides 10.1-volts dc
v o l t a g e s corresponding to the amount of
regulated as operating voltage to integrated
modulation applied to the signal. The
circuit V1. The regulated +195-volt dc supply is
discriminator output is fed to CARRIER SHIFT
the power source for zener diode regulator CR12.
meter M2 and audio circuits.
Section II. CIRCUIT ANALYSIS
voltage is applied through filter network Z1.
Filter network Z1 keeps all rf signals shorted to
ground. Plate voltage is fed through Z2, which
functions the same as Z1. Plate current flows only
when the FREQUENCY RANGE-MC switch is
wiring diagram which represent the ME-57A /U.
in one of the five frequency bands and keeps V1
5-4. Oscillator VI
nonoperating while changing frequency ranges.
This prevents unwanted oscillations which would
u. The local oscillator generates a signal that is
occur if V1 were kept operating.
fed to the mixer to be mixed with the incoming
c. The frequenty determining circuit is com-
s i g n a l from a frequency-modulated signal
posed of Cl, a two-section, air-dielectric, variable
capacitor, a n d o n e o f f i v e i n d u c t a n c e s
over a range from 32 through 512 MegaHertz
(represented by LB) selected by the
(MHz) in five bands, which are selected by the
FREQUENCY RANGE-MC switch. The
used to couple the oscillator output to the mixer.
MHz higher than the incoming signal, except on
the 500-1000 range where the second harmonic of
MC switch, and are designed to give optimum
the oscillator is used.
crystal injection, Capacitor C107 and resistor R7
b. A 5676 pencil triode is used in the shunt-fed
form a grid leak bias circuit.