February 3, 2003 6881076C20-E
3-4 Basic Theory of Operation: Power Amplifier
3.5.8 Vehicle Interface Port (VIP)
3.5.8.1 Remote-Mount
The VIPs allow the control head to operate outside circuits and to receive inputs from outside the
control head. There are three VIP outputs that are used for relay control. There are also three VIP
inputs that accept inputs from switches. See the cable kit section for typical connections of VIP input
switches and VIP output relays.
The VIP output pins are located on the back of the control head below the area labeled “VIP.” These
connections are used to control relays. One end of the relay should be connected to switched B+,
while the other side is connected to a software-controlled on/off switch inside the control head. The
relay can be normally on or normally off depending on how the VIP outputs are configured. The
function of these VIP outputs can be defined by field programming the radio. Typical applications for
VIP outputs are external horn/lights alarm and horn ring transfer relay control.
3.5.8.2 Dash-Mount
The VIP outputs are driven by a serial-to-parallel shift register. The output transistors are capable of
sourcing 300mA current. Primarily, these transistors control external relays. The relay is connected
between the collector and switched B+.
Each VIP input transistor is connected to a dedicated input port through transistors used for input
protection. These VIP inputs are connected to ground with either normally open or normally closed
switches.
3.5.9 Power Supplies
The +5V supply is a three-terminal regulator IC to regulate the 12V SWB+ down for the digital logic
hardware.
3.5.10 Ignition Sense Circuits
A transistor senses the vehicle ignition’s state, disabling the radio when the ignition is off. For
negative-ground systems, the orange lead is typically connected to the fuse box (+12V).
3.6 Power Amplifier
The power amplifier (PA) is a multi-stage, discrete-transistor RF amplifier consisting of the following:
• Low-level power controlling stage
•Drivers
• Final amplifier
• Directional coupler
• Antenna switch
• Harmonic filter
3.6.1 Gain Stages
The first stage buffers the RF signal, filters harmonics, and acts as a variable amplifier. All of the
amplifying stages are matched using transmission lines, capacitors, and inductors and are supplied
with dc from either A+, keyed 9.4V, or 9.6V sources. Following the last gain stage, PIN diodes switch
the signal flow either from the antenna to the receiver, or from the last gain stage to the antenna.
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