MM0474
(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.
Some
drift in the null will probably be observed. This is due to thermal drift of
the bolometer element.
(5) Once the null has been obtained place the reference
function switch in the RVG position (full counterclockwise).
(6) Record the voltmeter reading, which will be designated V1.
(Note
that this voltage is nominally the same as appears on the divider dials.)
(7) Turn on the RF power and move the V-REM-V switch to V.
(8) Record the voltmeter reading, which is V.
(9) Calculate the power using the expression:
P = K(2V1 - V) V
The proper value of K is obtained from Table 2.
Table 2.
Values of K for Various Bolometer Mount Operating Resistances (Gives
Power in Milliwatts)
d. Self-Contained Power Measurement.
This procedure is not recommended
where the highest accuracy is desired.
It has the advantage of being
completely self-contained, i.e., no other external voltage measuring equipment
is needed.
e. Measurement Procedure.
(1) After the initial steps of para. 4a have been followed, turn the
instrument on.
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