Ramsey Electronics FZ-146 Specifications download pdf (Page 103)

FX-146 • 103

soon as both strings are exactly on the same frequency. By tuning the one

string to the exact pitch of the other, you have corrected the phasing of the

two independent frequency sources. Pilots of multi-engine planes (or boats)

make slight RPM adjustments to get all engines in phase. If you have two

audio oscillators handy, listen carefully as you adjust both to EXACTLY the

same frequency. Another analogy is the process of tuning a BFO equipped

receiver to a perfect null or "zero beat." If you are exactly on frequency, you

hear nothing, even though the BFO and incoming signal are both fully

present. In a PLL, we want the "beat note" to be a perfect zero or constant

direct current (DC), and this DC controls the VCO.

What breaks the circle? What UN-locks the loop, the PLL? Let's think and

make a list of possibilities:

• VCO will not tune in proper frequency range

• Bad Reference Oscillator (IC, crystal, component?)

• Invalid "N" number?

• A physical break in the loop?

Caused by (what else?):

• Bad solder connections

• Incorrect components

• Defective components (rare)

• Incorrect programming

The preceding is about as untechnical as we know how to get in giving a hint

of how the PLL Frequency Synthesizer portion of your transceiver functions.

The Glossary of Terms in this book might give some additional help, but

there's really no substitute for just exploring the knowhow of modern

communications technology by whatever learning method works best for

you.

Now, let's take another look at the whole circuit in a more formal way.

The PLL Frequency Synthesizer IC:

• The MC145152 IC incorporates the equivalent of 8000 individual

transistors and contains the following circuits:

• A crystal reference oscillator governed by Y2, 10.24 MHz.

• A counter or "frequency divider" circuit set externally to divide the

crystal oscillator output by 2048, for a Reference Frequency output

of 5 KHz.

• A second counter or frequency divider that divides the frequency

from the Prescaler (U3) by the externally programmed number that

we call "N".

• A third frequency divider ("A") also used for programming

• Control logic circuitry which permit the "N" and "A" counters to

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Ramsey Electronics FZ-146 Specifications Page 103