Finally I did not yet get a null modem cable, so I tried to make it myself a simple null modem cable like the first image above. I cut my cable in the middle and I joined the 3 cables above. However my cables don't have the same colour as in the picture above. I have:
02 - light brown
03 - red
05 - black
I connected:
02 - 03
03 - 02
05 - 05
I opened the ends of the cable to see the connections, so it should be correct, but it does not work.
Klaus