Ramsey Electronics FZ-146 Specifications download pdf (Page 97)

FX-146 • 97

 F18. Install C35, 100 pf disc capacitor (marked 100 or 101). C35 couples

the VCO buffer to the receiver IC.

 F19. Install C94, a 3.9 pf disc capacitor (marked 3.9).

 F20. Solder 1/4" lengths of bare wire (trimmed from resistors or

capacitors) in the two test point holes marked TP2 and TP3. Study the

following optional test procedure before installing a similar test point at

TP1.

F21: TEMPORARY RECEIVER PTT/T-R CONNECTION

OMIT this step if you prefer to install ALL transceiver parts before any testing

or use of the Receiver alone. If you wish to conduct further tests or put the

receiver to work, it is necessary to solder a 5" length of hookup wire from

the hole marked "+8R" (near Q13, R112) to the hole marked "+8V" near

C29. In lieu of the switching done by the PTT circuit (Stage M), this

temporary jumper applies +8V to all +8R points on the board. (You also

have, of course, the option of wiring the microphone input and PTT circuitry

before testing the receiver.)

Even if you do not perform the following test, be aware that there is one

more step following this discussion (F22) - please don't forget to do it.

OPTIONAL VCO RECEIVER TEST OR INSTRUCTIONAL

DEMONSTRATION

At this point in building your transceiver, the VCO is functional but is lacking

any control voltage to varactor diodes D3 and D23 that would permit tuning.

Supplying this precision controlled voltage is, of course, the function of the

PLL Frequency Synthesizer that will be constructed next. However, for those

who would benefit from such a test or demonstration, it IS fairly easy at this

point to set up temporary manual or "analog" tuning with an ordinary

potentiometer.

Notice on the schematic diagram that the control voltage to the tuning diodes

comes from U5A through R47 and R25. Notice that a Test Point (TP1) is

conveniently located at R25. The purpose of TP1 is to permit measurement

of the precision voltage to the varactor diodes generated by the frequency

synthesizer's phase detector. Since no such voltage is yet reaching TP1, we

can put it there ourselves! If we connect a potentiometer as illustrated below,

the wire soldered to TP1 can be trimmed down later to serve as the intended

test point. The potentiometer will vary the voltage to D3 and D23, thereby

varying the VCO frequency and tuning your receiver.

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Ramsey Electronics FZ-146 Specifications Page 97