The PARS "PL" Tone Encoder
This device was developed to make available to PARS club members a means
of installing the necessary tone encoding to access the PARS repeater when it 
becomes neessary to incorporate the "PL" capabilities of the machine. c1980
              Input - 10 - 15 vdc                ^ = indicates gnd
                         +                       + = connect point
               r5        |        r4             v = adjustment
           +-\/\/\/--+---+---+--\/\/\/----+
           |         |       |            |
           |         = c1    = c2         |
           |         |       |            |
           |         ^       ^        Q2  |        r3      c8       tone
           +----------------\___________|/e ---+--/\/\/\---][-----> out
           |                           b|\c    |
       b |/ c Q1                         |     |
  +----+-|\ e                            |  c4 |
  |    |   \-----------------------------+--][-+
  \    |                                 |     |
  /    = c6                              |     |
  \r6  |                                 ^     |
  /    ^                                       |
  +---------/\/\/\-------+------/\/\/\---------+
  |          r7          |        r8           |
  |                      = c5                  |
  |                      |                     |
  |                      ^                     |
  |                                            |
  +----------][---------+----------][----------+
             c3         |          c7
                        |                  +------+
                        |                  v      |
                        +---\/\/\/---+\/\/\/\/\/\/+-----+
                             r2            r1           |
                                                        ^
     Parts List                           Specifications
r1 10k pot   c1 47mfd               PARS PL Frequency    103.5 hz
r2 3.3k      c2,c8 .05 ceramic      Avg Freq Range       95-115 hz
r3 100k      c3,c7 .027 mylar       Operating Voltage     10-15vdc
r4 3.9k      c4 .0039 mylar         Current Drain           3-4 ma
r5 6.8k      c5 .047 mylar          Avg Output              1 volt
r6 35k       c6 20 pfd NPO
r7,r8 100k 1% (all resistors 1/4w)  Stability - Less than .5 hz
Q1 2N3904                                       change 10-15 vdc.
Q2 2N3906                                       Less than .5 hz
                                                change for temp var.
                                 oOO0OOo
Installation and Operation:  Frequency is set by feeding the output into a 
counter.  Adjustment of R1 will bring the encoder to the correct frequency. 
Since the output of this encoder is quite high (1 volt), it will be necessary 
to connect the encoders' output through an insertion resistor to an injection 
point in the transmitter.  Values of this resistor range from 10k to 500k and 
is found experimently and varies with rigs.  Choose a value to obtain about 
500 hz of deviation.  Then tweak R1 for reliable results with the repeater. 
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PARS stands for the Poway Amateur Radio Society, Poway, California.
When we began installing these, we found that the best place to inject the 
tone was at the center of the diviaton pot.  These particlular encoders were 
pre-set at 103.? hz, which was the PL (1A) tone required to access the 
repeater.
Roy
... His was the nose that launched a thousand ships!
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