Broadband Hf Power Amplifier (Sheet 8); Power Generation Section (Sheet 9) - RF Technology Eclipse Series Operation And Maintenance Manual

The external output signal of T/R_RELAY, which is asserted low whenever the exciter
is keyed up, is used to switch MOSFET Q706 off. When Q706 is off, amplifier U700 is
enabled. When T/R_RELAY is high, then U700 is deprived of bias current and
VCO_OUT is then completely disabled.
5.8 1W Broadband HF Power Amplifier (Sheet 8)
The HF output of Sheet 7 (VCO_OUT) becomes the primary input to this circuit
(RF_IN).
This RF input is first amplified to a level of about +2 to +4dBm by U800, then it is
amplified by Q801 to about +20dBm (with full bias), and then it is amplified by Q804
and Q805 to +30dBm. The output stage gain is less above about 42MHz, so that the
peak output power falls to about +26dBm at 50MHz.
The effective gain of Q801 is controlled by adjusting the bias level (PWRCNTRL).
This can vary from 0.6V to nearly 6V, and is adjusted by a DAC output and a CPU
digital output, in Sheet 4.
The software monitors the forward power sense in the External Power Amplifier(PA) as
well as the Reverse Power, temperatures, drain currents etc. It does this via the serial
bus (formed by SCLK and MOSI) and the select pin for the ADC converter on the
External PA (PA_CS).
The software then automatically adjusts the PWRCNTRL bias to:
1) Keep the forward power at the level defined by parameter PA_SET_FWD_PWR
(see 4.1), unless,
2) If the reverse power is higher than
PA_SET_FWD_PWR*REV_PWR_ALARM/100.0 then the forward power is
reduced until the reverse power stops exceeding this limit, or,
3) The temperature of the PA output stage FETs exceeds 120C, in which case
forward power is reduced until this stops occurring.
5.9

Power Generation Section (Sheet 9)

There are three switch mode dc-dc converters in the board. These use monolithic
converters based on the National LM2595. Two of the converters are 12V converters
and one is a 5V converter.
The power in to the whole exciter is the voltage rail 28V.
U907 converts this down to 12V.
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5 CIRCUIT DESCRIPTION
RF Technology T50