21
Over-voltage and reverse voltage protection
Over voltage and reverse voltage protection is incorporated on the PA PCB. The over voltage protection is
provided by SCR1 and SCR2. These conduct when the input voltage exceeds about 17 volts. This causes
the gate voltage on P channel MOSFETs Q6 and Q7 to pull up to the source voltage, thus turning them off.
The power source must be removed for this circuit to be reset. Zener diode D21 does not conduct until the
input voltage reaches about 17 volts. In this event D21 allows current to flow into the SCR gates via
resistors R31 and R15. Transorb diode D1 absorbs any instantaneous voltage peaks over 18 volts.
For reverse protection, diode D14 will simply not conduct and no current will flow into the transceiver.
Auxiliary antenna socket
A relay, controlled by the microprocessor and mounted on the rear panel PCB, allows a second antenna to
be used, to permit for instance a separate receiving antenna See operators manual for further details. The
second antenna socket position in the chassis can also be used to locate the GPS BNC antenna socket
when the internal GPS receiver option is fitted.
Receiver RF amplifier
The receive RF pre-amplifier is a grounded gate circuit consisting of Q16, transformer TR7 and associated
components provide 8 dB gain at the front end of the receiver. This amplifier is preceded by a high pass
AM broadcast filter L7, L8, and associated Capacitors to prevent strong broadcast band transmissions from
interfering with the wanted signal. When listening to broadcast signals on the medium wave band, this filter
is switched out by the microprocessor.
Содержание 2000 Series
Страница 10: ...10 ...
Страница 29: ...29 To access components on the battery charger PCB the RF shield must be un soldered ...
Страница 45: ...45 Rear panel connectors ...