5.4
DUTY CYCLE/KEY-DOWN LIMITATIONS
The major heat generating component within the modules is the RF power amplifier which has a
maximum temperature limit that should not be exceeded. In addition, the temperature within the
module itself must be kept below the maximum temperature of the reference oscillator to ensure
that regulatory frequency stability limits are observed. As a result, depending upon the RF output
power, the supply voltage, and the ambient temperature, limits upon the average transmit duty
cycle and the maximum continuous transmitter on time exist. These limits are summarized below
for operation in still air:
Ambient Temperature (
C)
Duty Cycle (%) Key-Down Time (s)
3 watts RF output
25
30
45
50
5
10
6 watts RF output
25
20
30
50
3
5
Blowing air across the unit and/or adding a heat sink to the rear of the unit where the PA module
is located can significantly improve the duty cycle/key-down times. Ritron offers an option where
the case screws at the rear of the module are longer allowing heat sinks to be attached. Also, a
fan option is available from Ritron which can significantly increase the duty cycle, up to 100% at
room temperature in some cases. Contact Ritron for additional information on these options and
special instructions on attaching heat sinks without compromising the mechanical integrity of the
RF PA module.
