MM0474
(2) For improved accuracy of measurement results, Calibration Factor and
Efficiency are measured at selected frequencies across the operating range of
each mount, and the results recorded on the label of the mount. In addition,
each mount is tested on a swept-frequency basis to assure that interpolation
between measured points is valid.
NOTE
Do not remove polyfoam insert -- damage to the thermistor
element may occur.
(3) Each Model 486A Mount is designed to provide a good impedance match
(low SWR) over the full frequency range of its waveguide size without external
tuning.
b. Maximum Input. The Model 486A/power meter combination responds to the
average RF power applied. The maximum signal applied to the thermistor mount
should not exceed the limitations for 1) average power, 2) pulse energy, and 3)
peak pulse power.
Excessive input can permanently damage the Model 486A by
altering the match between the RF and compensation thermistors (resulting in
excessive drift or zero shift) or cause error in indicated power.
c. Average Power.
The 486A/Power Meter combination can measure average
power up to 10 mW. To measure power in excess of 10 mW, a directional coupler
(such as one of the Model 752 series) can be inserted between the mount and the
source. UNDER NO CIRCUMSTANCES APPLY MORE THAN 15 mW AVERAGE TO THE MOUNT.
d. Pulse Energy and Peak Power.
(1) In measuring pulse power, there is a limit on the energy per pulse
which may be applied to the mount. For a pulse repetition frequency (PRF) less
than 1 kHz, energy per pulse can be up to 2.5 Watt-sec; for a PRF 1 kHz and
above, up to 4 Watt-sec (for lack of space, only the lower limit is shown on
the mount name plate).
However, this energy limit applies only to pulses
shorter than 250 sec. In Figure 31, the pulse energy limit is translated into
a maximum power-meter reading for any PRF.
For pulses in this category,
allowable peak power is inversely proportional to pulse width but should never
exceed 100 Watts.
(2) For pulses longer than 250 sec, the peak power limitation can be
expressed in terms of PRF: 10 mW for a PRF below 1 kHz, 20 mW for a PRF 1 kHz
or above provided 15 mW average is not exceeded. In Figure 32, the peak power
limit is translated into power-meter reading versus duty cycle.
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