Functional Description
1 kW Amplifier
The 1 kW amplifier consists of the following main functions:
•
Linear RF power amplifier covering the HF band. The RF amplifier consists of 4 independent
amplification modules, whose outputs are combined to obtain the required RF output power.
The RF drive signal, applied to the RF IN connector, is amplified to the appropriate level, as
selected on the RM125/RM125R.
•
Harmonic filter. This is a low-pass filter whose purpose is to attenuate harmonics and other
undesired signals at frequencies above the actual operating frequency, before the amplified
output signal is applied to the RF OUT connector. The filter has 8 sub-bands: the filter that fits
the operating frequency is automatically inserted in the transmit path. The required frequency
information is received from the RM125/RM125R; in addition, the 1 kW amplifier measures
the actual frequency of the RF drive signal as part of its tuning process (if the frequency cannot
be measured, the highest band is selected).
•
Bypass circuits. These circuits automatically bypass the 1 kW amplifier and establish a direct
path between the RF IN and RF OUT connectors when power is not available, or a critical
malfunction is detected.
•
Control circuits. These circuits control 1 kW amplifier operation, interface with the driver
(RM125/RM125R), and take action to protect the amplifier when necessary.
•
Cooling subsystem, includes internal fans that enable operation over a wide range of
temperatures.
Overdrive Protection
The 1 kW amplifier requires a nominal drive power of approx. 40W. When operating the 1 kW
amplifier with the RM125/RM125R as driver, the input power is automatically adjusted by an
automatic level control to achieve optimal operating conditions for the amplifier.
However, if the input drive power exceeds about 80W (either because incorrect setting of the
operating conditions when using another’s vendor’s driver, incorrect connections or other possible
faults), the protection circuits prevent damage to the 1 kW amplifier by bypassing it.
High VSWR Protection
To obtain maximum forward power, the RM1200 should be connected to a low VSWR antenna system.
In case of excessive VSWR, for example, because of mismatch or damage to antenna system and/or
feed cables, the ALC circuits prevent damage by reducing the transmit power to safe values. Thus, the
RM1200 will always attempt to transmit at the maximum safe power in case of mismatch.
However, in case of excessive mismatch (for example, short or open circuit), the protection circuits
switch the 1 kW amplifier to the bypass mode: in this case, the transceiver is directly connected to the
antenna. This enables normal reception, as well as transmission, albeit at the lower power levels an
RM125/RM125R (or the transceiver used as exciter) can provide.
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