MM0474
Square-wave modulation is a special case of pulse modulation, and maximum
power-meter reading versus square-wave frequency is illustrated in Figure 33.
This figure also holds for sine-wave modulation.
Figure 33.
Maximum power meter reading versus square and sine-wave modulation
frequency.
(3) In the discussions above, the primary consideration is maximum power
or energy.
However, for modulation frequencies less than 100 Hz, the low
repetition frequency itself causes errors in indicated power. These errors may
be as large as 2% regardless of range or reading.
f. Drift.
Thermistors are inherently temperature sensitive devices.
A cold
thermistor mount connected to a warm piece of equipment or vice-versa, produces
rapid drift. FOR MINIMUM DRIFT ON SENSITIVE RANGES MAKE SURE THAT THE MOUNT
AND THE EQUIPMENT CONNECTED TO IT ARE AT NEARLY THE SAME TEMPERATURE BEFORE
MAKING A MEASUREMENT.
g. Zero-Set.
It is necessary to electrically zero-set the power meter before making
a power measurement.
To preserve the same zero reference through the
measurement, especially when operating on the more sensitive ranges, maintain
the same thermal environment when RF power is applied.
Three recommended
setups for zero-set are presented below:
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