Ramsey Electronics FZ-146 Specifications download pdf (Page 98)

FX 146 • 98

VCO AND RECEIVER TEST PROCEDURE:

 1. Make sure work area is tidied up and that the PC board has been

checked for stray scraps of wire, etc.

 2. Use your own hookup wire and potentiometer to connect to TP1, +8V

and GND as illustrated.

 3. Turn power switch OFF and squelch fully counter clockwise.

 4. Connect 12V DC, speaker and antenna (2' of wire will do).

 5. With power on and volume at a low level, s-l-o-w-l-y turn the

temporary tuning potentiometer. See if you can hear a local repeater,

nearby transmitter or business band transmissions. Perhaps the easiest

signal to hear is the local NOAA weather transmitter located around

162.5 MHz. Because the control is sweeping through FORTY MHz of

spectrum, actually tuning in a station will be VERY touchy.

The demonstration can be more interesting and useful if a digital voltmeter is

added to monitor the voltage changes at TP1, and a Ramsey Frequency

Counter is connected to TP2 or the top of R113. REMEMBER that the

indicated VCO frequency is 21.400 MHz LOWER than any signal you

happen to tune in. Observe how much frequency change there is per .1 volt

or less of voltage change. Stay on a given frequency for a minute or so and

notice how the indicated frequency drifts slightly either up or down. This

observation helps us appreciate the precision control that will be offered by

the PLL circuit. Finally, notice that the higher the voltage applied, the lower

the varactor diode's capacitance which means the higher the VCO

frequency.

If you do have a meter and counter connected, an initial setting of the slug in

L7 can be made now. Adjust the voltage for 4.0 volts and tune L7 to

approximately 138 MHz. (Note: final tuning of L7 will be even easier after the

PLL circuitry is completed). When you are finished with this optional

test,disconnect DC voltage. Then, cut the wire to TP1, leaving 1/4" soldered

in place to serve as a permanent test point. If you do not wish to conduct this

test, simply double-check the accuracy of your work in this stage and

proceed to the Frequency Synthesizer section.

 F22. Install U3, IC type 12017. Do not use a socket for U3, just be sure

to orient the notched end as shown on the board.

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Ramsey Electronics FZ-146 Specifications Page 98