T.E.M. A07B500S, Руководство пользователя

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A07B500S manual
Pag. 41
compensated. MOS-FET push-pull output is connected to another impedance transformer with a
4/1 ratio.
The 3 dB output coupler has a 250 Watt (power) resistor for its unbalance load, and before it, on the
same power source strip-line is another 25dB coupler; the unbalance between the two amplifiers is
reduced to minimum by regulating the input equalizers. The output harmonics of the amplifier are
already reduced a further 35dBc throughout the operating band. The output power, with a power
source of 50Vdc, can reach higher than 800 Watts with a efficiency above 70% throughout the
band. Such elevated power is not normally required, and to obtain a good efficiency for 500 Watts
output, it is preferable to power the final MOS-FETs with a voltage above 44 Volts. The
polarization in A-B class creates a total output power of between 1 and 500 Watts without problems
of instability. This value is automatically reduced when the temperature of the heat-sink reaches
values above 65
?
C. In fact, at that limit, a power control intervenes to reduce the value of output
power in order to compensate the increase in temperature. If the reduction exceeds 3dB of the set
value, an alarm is triggered which can be transmitted as an SMS, if connected to a GSM. Power
can be reduced to very few Watts of output, but if the temperature exceeds 85
?
C, it is cut off. There
is another thermal sensor which measures temperature of the power source, and it is this that cuts
off all power if the source overheats for lack of ventilation or a failure. The first thermal protection,
with control of output power, allows for operation even at environmental temperatures above 40
?
C,
with power gradually decreasing with the temperature. Meanwhile, the second protection
intervenes normally to shut the machine off if there is a lack of ventilation. It is also important to
note that a periodical substitution of the fan is recommended (at least once every two years) to
avoid triggering alarms caused by high temperature
5.10 DC-250 module
The DC-250 circuit filters the RF power signal and records forward and reflected power for
measurement and control. The whole circuit has a loss of approx. 0.1dB and does not require
ventilation. The low-pass filter is designed to reject all harmonics below 75dBc with a minimum
loss, and requires no regulation.
The directional coupler is comprised of two coupled lines in –30dB strip-line. Forward and
reflected power are sensed, compensating with precision the frequency response of the directional
coupler without affecting impedance adaptations. The average directivity is above 30dB and, as
such, precision of control and measurement is comparable to that of an average instrument of
measurement. The thermal drift of the diode detectors is thermally compensated to obtain an error
margin of less than 1% from 0
?
C to 40
?
C.