The fact that the MixW 2 uses a single COM port for CAT, PTT & CW makes it possible to have a smart CAT cable like below without having so many cables running between your rig and the PC. This is a better solution even from the RF point of view. I have constructed this for a YAESU FT 847 & will work for any other rigs which uses 3 line communication (TxD, RxD and GND) with the computer.
This can be started with a 9 Pin serial cable like this by cutting away the two 'sealed' connectors. You also need 2 seperate 9 Pin(or 25 pin) Rs 232 connectors (Select proper type (sex)) according to your rig and the PC connections. The circuit diagram is shown below. (sorry for the larger size in order to preserve the quality).
Description : There are 2 similar transistor switching circuits. One is diven from Pin 4 (DTR) and this is for CW keying. The other is from pin 7 (RTS) and this is for PTT. (You have to specify these to the MixW 2 also correctly). The TxD (pin 3) and RxD (pin 2) are directly going to pin 2 and pin 3 of the TRX CAT port forming a 'Null modem cable' required by the FT 847. Pin 5 of course is connected directly to Pin 5 of the CAT port since it is the signal GND.
Then comes the audio paths 'from' and 'to' the TRX. The audio out from the TRX is directly going to the 'microphone in' of the sound card undisturbed. The 'audio out' from the sound card goes to the PTT circuit of RTS (pin 7) through a 10 mF capacitor and then goes to the 'audio in' of the TRX. This line will be serving as the PTT line as well.
Construction : Usually it is not possible to assemble 2 normal NPN transistors , diodes and resistors inside the DB 9 connector. Therefore I used Surface Mounting Components technology to produce the PCB which exactly fits inside the connector as below, (The surface mount components are not clearly visible here)
Connectors
PC End : This side contains the (above) circuit board and the 2 number of 3.5 mm stereo male connectors. The speaker connector has a 10 mF capacitor soldered inside it, in order to have more space inside the DB 9 connector.
TRX End : This side has the following connectors
- 1) DB9 connector for the CAT port of the FT 847
- 2) 3.5 mm stereo connector for the DATA IN/OUT port
- 3) Stereo Phono jack (male) for the CW key input port
- 4) Stereo Phono jack (female) for external keyer paddle connecton.
Precautions : There are few things to keep in mind in order to get rid of RF feedback and other problems.
1) Always use shielded cables for audio extension lines at both ends.
2) Connect Pin No. 5 GND of both ends of DB9 connector to the outer casing of the DB 9 connector.
3) Have a seperate GND line between the TRX chassis and the PC chassis. The reason for this is, in some PCs the COM port shield is not properly connected to the PC chassis ground. There can be 10 to 100 Ohms between these which is enough to create gound loops and to generate RF Feedback and AC 'humm' etc..
4) Use shortest possible cables in all cases.
5) Connect unused wires from both sides to the ground. Don't let them open in any side.
Disadvantages of this type of a cable : Even though MixW 2 uses the same COM port for CAT and PTT, most of the other software do not use the same convention. Eg. Log EQF triggers the RTS and DTR 'high' when communicating with the CAT. That means, the TRX keys down as soon as you start Log EQF. This is just a one example and many other software we use for ham radio follow the same convention.
On the other hand, if some other software uses 2 different COM ports for CAT and PTT, this interface may not be useful.
Advantages : This is neat and only one cable between the rig and the PC which does everything. Looks simple & nice from the back side of the shack. The other COM port can be used for anything else..Modem, Mouse, TNC, Rotor etc.. This is good for portable operators. One cable and that's it.
No intermediate bulky boxes between the PC and rig. Everything is 'hidden' inside the connectors.
Conclusion : This smart cable works fine with FT 847 and MixW 2 combination. I hope it will work with any other rig which uses only 3 wires to communicate (TxD, RxD and GND).
Note : The purpose of this article is to share this idea with anyone who uses MixW 2, one of the best 'All in One' software I have ever seen.
After many requests from around the world, the complete unit is manufactured by Bravo Solutions and is available for USD50 including P&P.
- 73 DE 4S7AB Kamal.
- 4s7ab@qsl.net
- 2001-06-28
Another friend of mine George GM3KCY, who is a MixW user has tried another interesting method
George Says, Before connecting to the ICOM765 I have been doing some tests with the PTT circuit which I built into a 25 pin com port connector and using the RTS and shell of the connector Like I use with the other digital modes for the PTT. This didn't work for me.
I then tried a 1000 ohm reed relay connected from the pin RTS pin 4 and the shell of the connector and with a small diode from pin 4 to the shell to stop bounce and it worked. I then connected it to my transceiver and it is working just fine. I had to enter the set up and make a couple of changes like making the RTS the CW and the DTR not connected. The CW weight I left at 0 The Morse from the keyboard sounds very nice and I have done a test at 25 WPM and the report was FB. I don't have isolating opto couplers or transformers for an interface for the digital modes. Just a small home made switch [reed relay] and some control over the audio to the TXR.
Within the box is the 1K lin which is in series with the audio output from the sound card and then onto the padder circuit to maintain a 10 mV or less signal to the transceiver audio input. The relay at the top of the small vero board and the diode is the PTT to the transceiver. Very simple and compact and works well with the other digital modes. Only problem was being a CW operator basically I wanted to try out the Morse option and was finding difficulties with using the DTR output so now I just use RTS and it works well
ps. only one com port on this computer but I switch it around to my other equipment using a data switch and that all seems to work very well.
- 73 George GM3KCY
- one.bankie@ntlworld.com
George GM3KCY
GM3KCY - PTT Box
