Kenwood NXR-1800 Service Manual page 16

2.5.5.3 TX VCO/ TX PLL
2.5.5.3.1 VCO circuit
TX VCO consists of two VCOs, TX_L VCO and TX_H VCO.
TX_L VCO and TX_H VCO are switched by DC switches (DC SW: Q2008 and Q2009), according to the operating frequency.
TX VCO generates the carrier for the transmitter and the frequency range is 400 to 470MHz (E2 type), or 450 to 520MHz (E type).
TX_L VCO (Q2003) oscillation frequency range is 400 to 435MHz (E2 type), or 450 to 485MHz (E type), and TX_H VCO (Q2007) is
435 to 470MHz (E2 type), or 485 to 520MHz (E type).
The voltage control terminal "CV" is controlled by TX PLL (IC2000), and the voltage control terminal "ASSIST" is controlled by D/A
converter (DAC: IC78).
Note:
In the default condition, TX VCO stand by at a frequency a few kHz off the channel operating frequency while not transmitting.
The reason is that the nearby radios can be BUSY by radiated or conducted spurious of TX VCO, even though the repeater is not
transmitting. This function "Standby on Transmit Frequency" is FPU selectable.
2.5.5.3.2 PLL circuit
The circuit of TX PLL (IC2000) is basically same as RX PLL.
For the modulation input terminal "VCO_MOD" of TX VCO, the output frequency changes according to the applied voltage. This is
used to modulate the TX VCO.
The modulation input terminal "PLL_MOD" of the TX PLL (IC2000), is used to modulate the TX VCO output. The modulation data is
generated by the FPGA (IC60).
1-16 (No.RA094<Rev.002>)