[werk_ag]

comport = new SerialPort(cumulus.ComportName, cumulus.DavisBaudRate, Parity.None, 8, StopBits.One) {Handshake = Handshake.None, DtrEnable = true};

DTR is probably used for genuine Davis equipment which is why it is enabled
I am not sure if there is much you can do about it.

[/quote]

ah ah, very good, thanks  . I remember I saw that some years ago when I was working on another project.
When I will have the time I will try to change DtrEnable to false to see if it will make any difference.

Yes, if I'm not wrong, first Davis models use a real serial port.