Working Principle Of Vco; Two-Point Modulation - RCA RDR9000 Service Manual

Service Manual 8. VHF (136-174 MHz) Information

8.3.2 Working Principle of VCO

VCO employs Colpitts oscillator circuit (the RX oscillator circuit comprises D6014, D6015,
D6016, D6017and L6061; the TX oscillator circuit is composed of D7001, D7002, D7004,
D7005, and L7007). It obtains different output frequencies by changing the varactor diode's
control voltage (i.e. CV voltage). There are two types of VCO: TX VCO and RX VCO. Both
types control EMD22 to switch operating status via OMAP. RX VCO consists of the oscillator
loop and Q6012, to provide LO signal. TX VCO is composed of the oscillator loop and Q7003,
to provide carrier for TX signal.

8.3.3 Two-Point Modulation

In TX mode, the two-point modulation technology is employed, to obtain higher modulation
accuracy and lower 4FSK bit error rate. MOD-VCO and MOD-XO send the modulation signal
to the modulation end of VCO and the reference oscillator of PLL respectively to modulate TX
VCO and the reference crystal oscillator.
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