Auto freq. track for UO-14.
^^^^^^^^^^^^^^^^^^^^^^^^^^^
Auto UO-14 RX frequency tracking for TS-790/FT-736
------------------------------------------------------
 The doppler shift range in overhead pass reaches to 20kHz. It is essential
to tune-in RX frequency for good through put.
 I assembled auto freq. tracking for UO-14 FSK signal reception and achieved
good result.
[Block diagram]
RX discri.out<-- voltage comparater--INV--NOR--switching TR---> Down control
                      (Q1)           (Q2) (Q2)      (Q3)
                                           |
   G3RUH board  DCD -----------------------

[Circuit connection table.]

                GND         Q1:LM324 or TL084  Q2:74HC02  Q3:2SC945 etc.
                 |
              (C:0.01)
                 |    ----      ----      ----              -----
   *a<-(R:1M)--------3 Q1 1----6 Q2  4----3 Q2 1---(R:470)---B Q3 C---> DWN *c
     +12V--(R:8k)--- 2    |   -5     |   -2    |            -E    |
                 |    ----    | -----    | ----             | ----
                 |            |          |                  |
              (VR:10K)       GND         |                 GND
                 |                       |
                GND                      |          GND   +12V  +5V
    *b<-- G3RUH board DCD line------------      Q1   11     4
                                                Q2    7          14

*a: to RX discri out (=G3RUH board RX IN)
*b: to G3RUH board DCD line (U10 pin 13)
*c: to down control pin of mic terminal (TS-790 mic pin 3)

setting of VR:10k
        The discrimiator IC output level is 5.8V+-2V.
        Whitout RX signal, set the VR to Q1 pin 1 level turn HIGH->LOW.

In my case, I assembled the circuit on a small universal PCB and enclosed into
TINY-2 with NB96 board.

In the case of FT-736, DL signal polarity is different from TS-790 so
change as follow
     ------
     3 Q2 1------|>------> DL signal to mic terminal
     2    |    Diode (1S1588 etc)
     -----