MIL-PRF-1/1203K
TABLE I. Testing and inspection - Continued.
d. Four hundred and fifty MHz test amplifier. An amplifier consisting of the TUT with related circuits shown on figure 3.
(1)
The cathode cavity shall be of sufficient quality to maintain an unloaded Q of over 150 measured at the amplifier input
with the tube removed and a low-loss dummy-tube capacitor having a value within the range specified for input
capacitance inserted in its place. The heater circuit shall also be a component part of the cathode cavity such that the
unloaded Q will reflect any loss in input power due to the heater circuit. The cathode cavity and its components shall
provide a power match between the coaxial input and the cathode of the TUT.
(2)
The anode cavity shall be of sufficient quality to maintain an unloaded Q in excess of 600 measured with the TUT
replaced with a low-loss dummy-tube capacitor having a value within the range specified herein for output capacitance.
The anode cavity shall be capable of resonating all tubes having output capacitance within the limits specified herein.
An appropriate coupling loop or probe shall be provided to load the anode cavity in order to maintain an overall amplifier
bandwidth of 7.5 MHz when connected to its 50-ohm load.
(3)
The design of the tube contacting components shall provide for firm and consistent contacts to all tube terminals.
Sufficient shielding between input and output circuits of the amplifier shall be provided so that no indication is obtained
on the power gain test indicator when the dummy-type capacitor is substituted for the TUT and full signal is applied.
Both input and output resonant circuits shall be tuned to 450 MHz for shielding test.
e. Four hundred and fifty MHz noise amplifer. The amplifier shall have the following characteristics:
Center frequency:
450 MHz
Bandwidth:
2.0 MHz
Input VSWR from 50 ohms:
Less than 1.1
Noise figure:
Less than 6 dB (using Airborne Instrument Laboratory Argon Lamp Noise Generator, Model 70,
or equivalent.
Power gain:
Approximately 80 dB (shall be adjustable from 70 to 80 dB). The output shall be adjusted to
work into a calibrated 50-ohm load and shall be matched to a VSWR less than 1.2:1 looking into
noise amplifier output.
f.
Detector and 50-ohm load. The detector and load shall be the equivalent of the General Radio 874 VQ detector terminated in a
50-ohm load (General Radio 874 WM). A calibration curve shall be plotted to accurately establish the relation between rf
power into the detector and the detector crystal current as indicated on the microampere meter. The calibration curve is used
to accurately determine the Y factor in the noise figure equation.
g. Microampere meter. A Greibach, Model 500, Microampere Meter, or equivalent.
h. Dummy-tube capacitor. A dummy-tube capacitor is a capacitor used in checking the test equipment and in making the test for
adequate shielding between input and output circuits of the 450 MHz test amplifier TUT. Physical dimensions of the capacitor
shall be the same as for the tube except that the heater pins and the heater-to-cathode ceramic are omitted. Construction shall
be as shown on figure 4.
4/
Power gain test.
a. The power gain test shall be performed in the equipment as shown on figure 5.
(1)
Calibrated signal generator: General Radio Model 1021-P2, or equivalent.
(2)
Four hundred and fifty MHz noise amplifier: Same as specified for noise figure tests. (See 3/ e).
(3)
Detector and 50-ohm load: Same as specified for noise figure test. (See 3/ f).
(4)
Microampere meter: Same as specified for noise figure test. (See 3/ g).
b. Procedure. With signal generator switched directly into detector and 50-ohm load, adjust output for approximate midscale
indication on microampere meter and note output, P1 (calibrated in decibels), from signal generator. Switch 450-MHz test
amplifier into circuit with tube inserted and reduce signal generator output until the same approximate midscale indication is
again obtained on the microampere meter and note the signal generator output, P2. Power gain = P1 - P2.
5
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