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To communicate between the Yaesu 897 an the CAT software HamRadio Deluxe U need a interfase (CAT cable). For this purpose Yeasu has come up with a expencive cable. This is also the case for audio, if you want to use digimodes.
I want to use both, so i did a search for alternatives on the internet, and found lot's of solutions, but not a good designe for both options. So i combined two simpel solution into one box. (see picture 1 and 2 below)
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In the commercial version from Yaesu there is a miniature MAX232 assembled into the RS232 plug. This is way over my capabilities, so i wanted to use conventional parts.
The MAX232 needs 5 volts to operate. The CAT interface on the FT897 has already a connection on 13,8 volts by 3,15 amps. So it's easy to make 5 volts with a 7805 regulator. (see scematic picture 3 above). The condensers for the 7805 are 100 nano Farad, and the condensers for the MAX232 are 1 micro Farad. The plug pin outs are seen from the solder sides of the plugs.
VERY IMPORTENT !!! Never, NEVER pull out the CAT plug if the transceiver is turned on. !! Yeasu has secured it's CAT port's on the FT897 (FT857, FT847, en FT817) with a miniature fuse of 3,15 amps. If this blows the CAT commands don't come trough and is unusable.
The schematic is pretty strait forward
The PTT is operated trough RST line on the RS232 plug. To divide the computer and the radio i have used a opto coupler 4N25. Some programs use alterative commands and turn the potential of the RST line. (potential low is tricker). This causes unwanted PTT trickering. The solution to this problem is to put a mini switch in the RST line, to manually override this command. To indicate that PTT is trickerd i have also put a led with a 1 K resistor into the RST line.
For use of digimodes i make use of the sound card of my laptop. For dividing the computer and the FT897 i used 1:1 transformers. These are the only parts used to get audio through to the computer.
There is another important part that is not on the schematic. To eliminate RF from the FT897 i have put two RF chokes into both cables (CAT and Audio) These are easy to make. Take a T200 farriet core (NOT iron) and make 6 turns of cable trough the core. Take the cable to the other side of the core en make another 6 turns (see picture 4 above)
This system works three years now with no problems with either program. I have made numerous QSO's on PSK31, SSTV, Packet and more, together with HamRadio Deluxe.
This is an easy to build solution to operate both CAT and digital modes.