USB GPS pretends its a serial port

I'm trying to get data out of a USB GPS device, PL-2303. USB to Serial Bridge Controller.

So I tried this.

sp = new SerialPort(portname, 开发者_StackOverflow9600, System.IO.Ports.Parity.None, 8, StopBits.One);
sp.Open();
while (sp.IsOpen)
{
string serialPortData = sp.ReadLine();
}

The connection is open - but no data is received. Do you think its because I'm trying to connect to a USB device by opening a serial port? Or do you think its because the GPS data isn't being received?

---

You probably have the wrong baud rate. Try the standard settings for NMEA.