G3RUH 9.6kbps modem connection need mod. to both TX and RX. of 790.
| TX: | connect new 1kohm R to the point D81 and R358(1k ohm) OR connect to CONNECTOR-31 directly. |
| RX: | IC8(MC3357P)---for main RX, IC1(MC3357P)---for sub RX pin #9 is the point to draw RX signal. usualy, sub RX is used for satellite communication as TX/RX freq. is different. But I drew both main and sub signal and switch them with a microrelay.This relay can be controled with main panel SW 144ATT.(see 790 manual). |
These mods. are essential for G3RUH 9.6kbps, but also usable for FO-20 PSK. BUT.....with my experience, there is many trouble to use this mods. for TAPR PSK modem. TX audio level setting, RX noise (MC3357P pin#9 has 455khz wave element).....and so on.
So, I use ACC2 for TAPR PSK modem (also usable for 1200AFSK)
ACC2 connection 4---GND 9---PTT 11---TXD audio signal in 1 --3.3k---\ 3 --3.3k---/ connect together to RX audio.
two small 1/8w 3.3k regitor mixes main and sub audio, so it is able to use for cross band full duplex and mono band half duplex operation. These registor can be mounted in ACC2 13 pin plug.
UP/DWN control from TAPR PSK modem to 790 U12 and JP5/6 setting
| U12 | 790 mic terminal | ||||
| pin 8 | ---- | D | ------ | UP | pin 4 |
| pin 5 | ---- | E | ------ | DWN | pin 3 |
| G | --- | B | ------ | GND | line |
pin 6 and pin 7 must be jumpered and connect to ground.
I found a possible solution in an old AMSAT-DL magazine No. 3/1992 page 21
--------------
| |
| +5V |
| | | -------
| --- --|6 3|------o---------o +5V
| | | | | |
| |5K |<----|7 1|-- ---
| | | | 1/2 | | |2K2|
Discriminator ----- | --- | LM339 | | | |
(Pin 9 IC1 o---| 22K |--o | ------- | | |
SUB-Band) ----- | --- | ---
| /// | |
| ---o---------o UP
| |
-------------- ---
| \ / LED (low cur.)
| ---
| |
| ---
+5V | ///
| | ------- |
--- --|5 2|-- +5V
| | | | | |
|5K |<-----|4 | | ---
| | | 1/2 | | |2K2|
--- | LM339 | | | |
| ------- | | |
--- | | ---
/// | | |
| ----o--------o Down
| |
| ---
| \ / LED (low cur.)
| ---
| |
| ---
| ///
|
|
|
o-------------------o GND
|
---
///
that's all, i hope you can employ it...
Bye, see you on Sat..
vy 73 es 55 de Thomas (DG6FCP @ DB0AIS.#HES.DEU.EU also on UO-22 and KO-23)
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