Synthesizer

AE/LZB 119 1902 R1A

divider consisting of resistors R116 and R117. The output of the divider circuit connects to power control buffer amplifier N102-B, Pin 5 (+IN). The output of N102-B drives Pin 1 of the power amplifier.

Power Control Buffer (N102-B)

A regulated 5.5 Vdc is applied to power control buffer N102-B, Pin 8 (V+). The buffer circuit is a shaping circuit which provides a control voltage on Pin 7 (+OUT). This voltage after passing through resistor R120 is typically 2.5 Vdc to 3.0 Vdc at 3 watt output and can be metered at test point TP103. This control voltage connects through filter capacitor C138, RF choke L113 and resistor R105 to power amplifier N101, Pin 1 (Pin/Vc). This voltages regulates the power output of N101. The output of the PA is increased or decreased by the DC level applied to N102, Pin 1. The feedback loop is stable when the output power level produces a detected level equal to the level prestored as a tracking value equal to 3 watts.

Transmit Low-Pass Filter/Antenna Switch

When the transmit circuit is keyed (Push-To-Talk switch pressed), SW_B+ (7.0 Vdc) is applied through RF choke L105 to PIN diode V100. With 7.0 volt applied, V100 and PIN diode V101 are forward biased. The RF signal is then allowed to pass through the low-pass filter to the antenna. The 6.2 volts on the cathode of V100 connects through inductor L103 to the anode of PIN diode V101. Capacitor C108, L103 and C109 make a parallel resonant circuit which prevents RF from flowing into the RX port. The voltage on the cathode of V101 (5.3 Vdc) connects through inductor L104, capacitor C112, resistor R100, capacitor C113 and inductor L107 to the input of the MMIC buffer amplifier (See MMIC Buffer Amplifier).

and connected through D1, Pin 133 (TDX) to X21-13 (TXSIF_DSPDATA). This signal can be metered at test point TP4. This connection then connects through X11-13 to HILLARY D701, Pin 77 where it goes through a TX DSP INTERFACE. The output of the interface applies the digitized audio to the input of a sigma/delta modulator or DAC. In the sigma/delta modulator a sample of the audio is taken at a 19.2 MHz rate. This generates a pulse that the width varies with the audio. The outputs of the DAC are through D701, Pin 15 (MODI), Pin 14 (MODI_B), Pin 16 (MODQ) and Pin 17 (MODQ_B). The pulse rate of each of these outputs is 9.6 MHz or one-half of the 19.2 MHz clock rate. These outputs are connected through low pass filters to the inputs of JACQUI N150 where modulation takes place. The output of the low pass filters is a true analog signal consisting of complex wave forms and a pulse of 800 mV Peak-Peak.

Dual Synthesizers (N203)

There are two synthesizers in the synthesizer circuit. One is the main synthesizer which generates the 1st LO frequency (1011.2 to 1016.2 MHz). The other synthesizer circuit is the auxiliary synthesizer which generates the 2nd LO frequency (76.65 MHz). These synthesizer circuits are programmed by STROBE 1, CLOCK and DATA. These

programming inputs also go to JACQUI. The only difference is that JACQUI uses STROBE 2. This is so that when strobed, the programming information gets written to

the proper device. The main synthesizer can be programmed in 12.5 kHz steps. These inputs can be metered at TP205 (CLOCK), TP206 (DATA) and TP207 (STROBE 1).

Transmit Modulation

The microphone input is through capacitor C300 and resistor R301 to operational amplifier N300, Pin 2 (-A) (Refer to Schematic Diagram sheet 10). The output of N300 is on Pin 1 (Out A). This output is connected to DEBBIE D601, Pin 19 (AUX). This audio signal is amplified, limited, passed through a low pass filter and an encoder circuit where the analog signal is digitized. The digitized output of the encoder connects through D601, Pin

35(DPCO) to HILLARY D701, Pin 41 (PCM_CDCMIC) where it is connected to a PCM interface. The output of the interface connects through D701, Pin 68 to the DSP module through X11-18 (See Schematic Diagram, Sheet 13). The actual connection to the DSP board is at X21-18 (PMC_DSPMIC). The transmit digitized audio can be metered at test point TP6 on the DSP board. This signal is then connected to D1, Pin 63 (DR). The audio is filtered

Bilateral Switch (N201)

Bilateral Switch N201 selects the loop filter required for programming the main VCO in 12.5 kHz steps. A +5 Volt signal (LOOP_SEL) from HILLARY connects to N201, Pin 5 (2_C Control) causing N201 to switch in the required resistor-capacitor combinations. The selected loop connects to the VCO at U200, Pin 2 (Vcont).

Main Voltage Controlled Oscillator (U200)

Asignal from HILLARY (VCO_BAND_1) turns transistor V201 on or off to select the band over which the VCO will operate. The collector output of V201 connects to U200, Pin 10 (SW). The output of U200 on Pin 8 (Output) connects through buffer transistor V200 to the RX_ LO through coupling capacitor C208. The TX_LO is taken from the voltage divider consisting of resistors R203 and R205. The feedback for the synthesizer circuit is taken from