Ramsey Electronics FX Series Manual page 86

test point. The potentiometer will vary the voltage to D3 and D23, thereby
varying the VCO frequency and tuning your receiver.
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 or
a nearby transmitter. Because the control is sweeping through FORTY
MHz of spectrum, actually tuning in a station will be VERY touchy. Since
the 220 band is sparsely populated, it may be difficult to chance upon a
signal without first setting up a QSO.
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 HIGHER 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 251 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.
F19. Install U3, IC type UPB569. Do not use a socket for U3, just be
sure to orient the notched end as shown on the board.