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Model 5340A
Theory of Operation
R16 are terminating resistors for each amplifier. The output of U5B(ll) feeds to the first decade
count board A22. The amplifier h a s a gain of about 30 dB a n d is dc coupled. A stable dc output
level is achieved by feeding back part of the output signal via operational amplifier U1 to the
input of U3. U1 detects any difference between the average (dc) level of U5(12) and the wiper of
R l l . Any imbalance produces a change in the level
back for the amplifier chain. C13, C14, and R4 give U1 a very slow time constant. Keeping the
output stable yields the best sensitivity for the counting circuits on A22.
4-197.
R14 provides minor feedback loops within the wideband amplifier to flatten the fre-
quency response.
C21 controls the high frequency response of the circuit to eliminate any
possible counting of noise.
4-198. U2 circuitry is a detector and comparator that determines if a signal below -225 MHz is
present. If
this will take precedent over energizing the operation of the phase lock mode of
so,
the instrument.
The presence of a signal causes CR5 to reduce the positive charge on C19
obtained through R21. This is matched by CR4 and C20 on the other side of the comparator U2.
A low pass filter (L5)
included
is
the other leg of the amplifier inputs.
reducing the Q.
4-199. If a signal exists below -225 MHz, CR5 places a voltage on C19 which is less positive than
that on C20, this will flip the comparator to a TTL high on U2(7). This tells the counter to imple-
ment the direct count mode. If the signal is higher in frequency, the voltage on C19 will increase
because of filter L5. The voltage on C20 will be less positive than before since a greater signal
level is coupled through the high pass filter C16, L6, and L7. Thus U2 will flip with pin 7 going to
a
signal that is strong enough to be counted will flip U2. This eliminates unstable displays. R21
and R20 keep a small amount of current flow through CR4 and CR5 to increase the sensitivity of
the detector to small signals that would not normally turn on the diodes. L1 through
associated capacitors are power supply filters. The output signals of U2 are valid only during
direct count check (Test #8). During other times, the outputs of the VCO's (A10 and A12) may
cause A17U2 to incorrectly indicate the presence of a direct count signal.
4-200. A18 STANDARD OSCILLATOR ASSEMBLY, 05340-60036
4-201. See Figure 8-24 for the schematic diagram of A18. The temperature compensated crystal
oscillator (TCXO) supplies a 10 MHz sine wave on pins
consists of +5 and -5 volts dc. The
V.
in Section
4-202. A18 OPTION 001 OSCILLATOR ASSEMBLY, 10544A
The 10544A Oscillator (Figure 8-24) is used when Option 001 is installed.
internal oven and controller that maintains a constant temperature, with a resulting stable output
frequency on pins
and A.
4-204. Any 5340A that is wired for Option 001 will work when the standard oscillator is installed.
This may be helpful in troubleshooting. To install Option 001 in a n instrument not so equipped,
see Section VII: The 10544A is factory repairable only. Adjustment procedures are contained
in Section V.
4-205. A19 INTERFACE A ASSEMBLY, 05340-60031 AND A27 RESOLUTION SWITCH
ASSEMBLY, 05340-60026
4-206. Interface A Assembly (Figure 8-25) provides the control signals necessary for completing
and displaying a measuremndnt. The circuitry associated with U5 selects either the internal 10
internal oscillator; U5B1 U5C, and R12 are used for the external oscillator.
buffers for the oscillator signal.
4-44
at
one leg and a high pass filter (C16, L6, and L7) is installed in
in
and R17 control the response of the detector by
1
and A for use in the 5340A. Input power
TCXO
is factory repairable only. Adjustments are contained
R13, and
L4 and
It has a n
form a Schmitt trigger for the
U2B
U2A
and
serve as
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Troubleshooting
