MIL-DTL-22442/1C(AS)
18. Amplifier impedance. Unless otherwise specified, the input impedance to the amplifier
shall be 5 (+10, -2) ohms at 1000 Hz with the output under load.
* 19. Amplifier tests. The following amplifier measurements shall be performed using the test
circuit of Figure 7 except that a true RMS ac voltmeter (see 6.4.1.1 of the general specification)
which is calibrated to the 50 microvolts level may be substituted for the lock-in amplifier. Unless
otherwise specified, the DC bias shall be set to 27.5 ± .5 volts as measured across the DC bias
supply terminals when placed in the circuit. Unless otherwise specified, the nominal input
voltage to the amplifier shall be 250 (±10) microvolts, and the amplifier output shall be
terminated with a non-inductive, high precision (±1%) resistive load equivalent to the nominal
load impedance. The input voltage to the amplifier is provided by the M22442/l-6 shielded
attenuator circuit, which provides 10,000 to l attenuation (80 dB). The input voltage to the
amplifier under test shall be determined by measuring the input voltage to the calibrated
M22442/l-6 attenuator and dividing by 10,000. Thus, a function generator output level of 2.5
volts will provide the nominal 250 microvolts to the amplifier under test. Any variation on the
test circuit of figure 7 must be approved by the Qualifying Activity (Naval Air Warfare Center,
Aircraft Division, Indianapolis) prior to acceptance of the test results.
a. Amplifier set-up procedure. Using the test circuit of figure 7 before the amplifier under
test is connected, set switch S20l so that R20l is out of the circuit (S20l shall remain in
this position throughout the test sequence until the impedance test procedure of
Requirement l9(f) is performed). Adjust the signal generator for a 2.5 volt signal into the
shielded attenuator at 1000 Hz. Connect the amplifier under test and perform
measurements specified below.
b. Amplifier frequency response (voltage gain) and linearity. The gain of the amplifier
shall be determined using the test circuit of figure 7. The output voltage shall be
measured using a spectrum analyzer (see 6.8.1.3) of the general specification or voltmeter
(see 6.4.1.1) of the general specification, and the voltage gain calculated in dB using the
following formula:
Gain (dB) = 20 log (Vout/Vin)
As a minimum, the gain shall be measured at 400, 1000, 1600, 2000, 2400, 3000 and
6000 Hz to insure conformance to the requirements of Requirement 13. The linearity
requirement of Requirement 16 shall be checked at 1000 Hz by setting the amplifier input
voltage to 50 microvolts and increasing it slowly to 500 microvolts. The amplifier gain
shall remain constant within ±2 dB.
* c. Amplifier input power measurement. The power supply shall be adjusted so that 27.5
volts dc appears across the output terminals of the DC bias supply when placed in the test
circuit. The frequency generator shall be set to 1000 Hz. The input current shall be
checked with a DC current meter.
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