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2. RX Unit:
The R Pre-Amp utilizes GaAs FET Q6 (MGF1302) and three-terminal Regulator
IC1 (78L05A), so that a high gain amplification with low noise figure is achieved.
When to operate the RX pre-amp alone, with POWER SWITCH turned OFF, turn
ON RX AMP SWITCH. Then, carrier controlling IC201 (NJM2072D) and
switching transistor Q201 (2SA966) will supply voltage to Relay RL5 and the
pre-amp at the RX state, so that a reception gain of approx. 15dB is obtained.
At the TX state, the voltage supplied to RL5 and the pre-amp becomes zero,
where the output power of the transceiver inputted from J101 is outputted
directly from J102 to the antenna.
3. WARNING Circuit:
The almost all part of WARNING circuit is incorporated into the control unit inside
the front panel where tight RF shielding is provided.
Each detection unit utilizes a CM-type directional coupler, Excessive Input
Detection Circuit being installed at the input side of DRIVER AMP, and SWR
Detection circuit being installed at the output side of MAIN AMP.
Each detected voltage is amplified by OP Amp. IC204 (NJM2904D) and the relay
controlling transistor Q203 (2SC3419Y) respectively, and turns OFF Power
Supply Relays (RL6 and RL7) to halt the transmission in case a warning status is
detected.
Two thermal sensors (SW101 and SW102) are installed.
SW102 increases the voltage of the line flow fan from 13VDC to 20VDC causing
the line flow fan to effectively run at its full speed when the temperature of the
heat sink exceeds 50• Ž .
SW101 turns OFF the power of the carrier controlled switching circuit to halt the
transmission preventing the power transistor from being damaged when the
temperature of the heat sink exceeds 70• Ž .
The HL-350VDX utilizes an indirect DC main power control circuit where the
power is turned ON/OFF by the Power Relays (RL6 and RL7). Diode D24
(1N5402) being inserted in series to the wound coil of the relays, no current will
be run in the wound coil even if POWER SWITCH is inadvertently turned ON
with a wrong DC power polarity connection.
Thus, the relays will not be activated, so that a safe protection is secured.
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