High power—Technical description
NGT Transceiver System Technical Service Manual 233
High-power ALC Adaptor PCB
This unit detects the output power from the external amplifier and the SWR of the
antenna, then produces a control signal for the NGT. Under this control signal, the NGT
varies the drive power to produce the appropriate output of 500 W or 1 kW PEP.
The output of the forward power detector D1 is applied to the base of V1. The output
from the emitter of V1 is connected to the input of IC1 pin 3. The output of IC1 produces
the ALC voltage to control the NGT. R15 (ALC ADJUST) varies the gain of IC1, which
determines the nominal PEP output level of the amplifier when matched to a 50 Ω load.
The output of the forward detector D1 is also applied to V2 via an averaging circuit
formed by R7, R9 and C10. When the average of the signal exceeds the peak detector
circuit V1, V2 takes control and reduces the output power (this occurs on signal tones
such as CW (Morse) and in some data transmissions).
The output of the reflected power detector D2 is applied to the base of V3. If the SWR is
greater than 1.8:1, the output voltage of V3 will be greater than the signal on V1, so the
power is reduced as the SWR increases.
Drawing 04-03407
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