User's Manual

SECTION 1: THEORY OF OPERATION
IPM8-FCCRpt.doc Page 8
The lower op amp (U9B) amplifies the signal from the low pass filter and applies it to the VCO via the
VCOMOD output. Pot RV2 and RV1 are used to adjust maximum deviation.
Injection Synthesizer
The synthesizer chip (U14) is the major contributor of the injection synthesizer. This device contains the
key components of a phase locked loop (PLL), including a prescaler, programmable divider, and phase
detector. The selected frequencies are loaded into U14 as a clocked serial bit stream via the PLL_DATA,
PLL_CLOCK and PLL_ENABLE signals.
Frequency stability is determined by a temperature-compensated crystal oscillator module (VCTCXO)
(Y2) at a frequency stability of 1 PPM from –30C to +60C. This device has an input (REFMOD) that
accepts transmit modulation and voltage from a RX FREQ ADJUST pot. The pot allows the receiver to
be fine-tuned to the exact operating frequency.
Two (2) voltage control oscillators (VCO) are formed by integrated low-noise oscillators with buffered
outputs (VCO2 and VCO1) and associated circuitry. The VCO’s generate receiver and transmit injection
signals. The receiver control voltage is generated by the phase detector output (PDOUT) of U14 driving a
loop filter consisting of R39, R42, C50, C51, and C70. It integrates the pulses that normally appear on
PDOUT into a smooth DC control signal for VCO1. The output of VCO1 is split by three two-way splitters
(U10, U12, and U13) leading to outputs RXINJ1 and RXINJ2. A second output of U40 is returned to the
synthesizer FIN input via RXFB. This completes the loop signal path.
Transmitter/TR Switch
The transmitter section consists of a driver amplifier (U18) and a final power amplifier (U15) installed at
the top assembly. To transmit, 5-volt power is applied to the KEYPWR line. PA12V line is also powered
up. This causes power amplifier (U15) to boost the RF power to the desired level. Up to 40 watts are
available from the transmitter. Harmonic suppression is provided by C82 and L11.
Power and Analog Ground
These sections consist of the power supplies and transmit control circuitry. Power from the vehicle’s
battery appears at VBATT. Diode D1 protects the voltage regulators by clamping any transient spikes on
the supply line. Such spikes typically occur while the engine is started. The supply line powers a series
of voltage regulators and the transmitter control circuitry, as follows:
 Voltage regulator U21 powers the transmit driver and T/R switch diodes as controlled by the
microcontroller.
 Voltage regulator VR2 provides a low noise 3.3-volt source for the radio electronics.
In the transmit control circuitry, to transmit, the microcontroller makes TXKEYOUT* high. Forcing the P-
channel device to conduct, applying 12-volts via PA12V to the transmitter power amplifier bias pins.