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)
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73s sueo asato JA6FTL
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