P
0
..... P
10
Program Select pins from Channel Selector switch. (Sometimes called "D" for ''Data'' rather
than "P" for ''Program''.) These pins control the actual channel selection. They may control selection
through straight binary coding, BCD, or ROM. The sub-numbers indicate the weight or significance of
each pin. For example if there were 8 programming pins, P1 to P8, P1 would be in the "least
significant bit" and P8 would bethe "most significant bit".The higher the sub-number, the greater the
weight of that pin.
NC No Connection. An unused pin May actually be disconnected inside the chip, or simply not used
for that particular rig' s PLL circuit.
Modification methods
A TYPICAL PLL SYNTHESIZER
Refer to the figure, which is the PLL circuit of perhaps the most common AM PLL rig ever made. It's
been sold under dozens of brand names, and uses the ever-popular PLL02A IC. The SSB and export
multimode versions of this circuit are very similar; there are only minor differences relating to the SSB
offsets and FMing the VCO.
A PLL design may be categorized very generally by the number of crystals it uses, and by whether its
VCO is running on the low or high side of 27 MHz. This particular example is actually the second
generation of the PLL02A AM circuit; the original PLL circuit used a total of 3 crystals.
The key to synthesizing all of the required frequencies lies in the Programmable Divider. That's the
only PLL section that you can control from the outside world by means of the Channel Selector. Which
is where it all starts.
Suppose you choose Ch., 26.965 MHz. When setting Ch.1 the Programmable Divider (PD) receives a
very specific set of instructions at all its programming pins, which are directly connected to the
Channel Selector. This specific set which we have called its "N-Code", applies only to Ch.l. It's just a
number by which any signal appearing at the PD input pin will be divided.
Binary Programing
Refer now to Programming Chart, which summarizes the important operating conditions by specific
channel number. A chart like this one is normally included with the radio's service manual.Often
though certain facts not directly related to the legal 40-channel operation are left out, so I`lll be filling in
some missing blanks for you.
Programming Chart for PLL02A
To Next Page
Loading...
