MM0474
(2) The bolometer mount should be attached to the RF source with the RF
turned off.
(3) Place the reference generator function switch in the NULL position
and the V-REM-V switch at V. Adjust the divider dials to read zero.
(4) Turn the main divider dial clockwise until the meter deflects to the
right, then turn the dial back one division. Repeat this operation with each
successive dial until the final null is obtained with the ten-turn dial. Note
that since the null detector is an integrator it is not necessary that the
meter pointer be on zero, but only that pointer movement be stopped. Again,
some drift in the null will probably be observed. This is due to thermal drift
of the bolometer element.
(5) Record the divider dial reading as V1.
(6) Turn the RF power on and repeat steps (3) and (4).
(7) Record the second divider dial reading as V2.
(8) Calculate the power using the expression:
Again the proper value of K is obtained from Table 2.
5.
PRECISION POWER STABILIZER (FIGURE 7).
a. The reference generator is also designed to be used as a precision
power stabilizer. It requires use of an external modulator which may be either
a PIN diode or ferrite type. The PIN output has a limited current capability
to protect delicate PIN diodes; the MOD output is capable of delivering up to
300 mA to the modulator. Both outputs swing negative with an increase in RF
power.
In addition, either output may be used to control ground-referenced
grid-leveled sources.
In this application, it may be necessary to attenuate
the stabilizer output if the signal source contains its own leveling amplifier,
because such amplifiers usually introduce enough phase shift to cause
oscillations. They are generally much less stable in terms of long-term drift
performance will be obtained using the reference generator in the stabilizer
mode to provide all of the necessary gain in the stabilizing loop. When used
as a stabilizer, the instrument provides the equivalent of an extremely high
resolution attenuator, because of the 1 ppm resolution of the 6-place divider.
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