>>> VCO DRIVER <<<

 

Figure 1, VCO Driver Circuit Diagram

  The circuit shown above will provide 12 volt power and the DC level (CV) needed to tune the LOA5C, VCO1K, and VCO2K Voltage Controlled Oscillators through their full frequency range plus providing frequency modulation (Delta F).  The CV terminal of this circuit connects to the tuning terminal (V-T) of the VCO assembly.  Adjustment of R7 will set the center frequency (CF) of the VCO assembly, and the AC amplitude at the M terminal will determine how far the frequency will deviate (Delta F) around the center frequency (CF).  For example, a 2 KHz, 1V P-P signal at the M terminal will deviate the frequency of the LOA5C approximately 5 MHz P-P around the center frequency (CF +/- 2.5 MHz).  The frequency deviation (Delta F) is scaled up or down linearly, 10V P-P yields 50 MHz deviation (Delta F) and 0.10V P-P yields 500 KHz deviation (Delta F).  The frequency deviation (Delta F) and other specifications of all 3 oscillators are shown in the table below.

Model Number

Frequency Range (MHz)

Power Output (dBm)

Power Supply Voltage (V)

Power Supply Current (mA)

Control Voltage (VDC)

Delta F MHz*

LOA5C 62.5 - 500 -1 +/- 18 +70/-8 1 - 16 see note 1

LOA1K

265 - 1060

  7

+/- 18

+83/-8

1 - 16

see note 2

VCO2K

1060 - 2120

  8

+12

+28

.5 - 20

  80

* CV = 8 VDC; M = 1 VAC P-P

Note 1:  divide-by-2: 20 MHz, divide-by-4: 10 MHz, divide-by-8: 5 MHz

Note 2: divide-by-2: 33 MHz, divide-by-4: 17 MHz

  R7 provides course frequency control. To fine-tune the VCO, set the VCO center frequency a few MHz above the desired value with R7, and with a positive adjustable supply of 0 to 100 mV connected to the M terminal, increase the voltage at M from 0 to a point where the oscillator frequency is reduced to the desired value.

Figure 2, VCO Driver Printed Circuit Assembly

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Figure 3, Driver & VCO Wiring Diagram

 

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