From my previous link:
Amazingly there are two versions of the EM-408 with the same part number. The standard version uses TTL voltage levels on its serial output (idle is 2.7V, the start bit and logic 0 are zero volts). The alternative uses RS-232 voltage levels and polarity (idle is -6.8V, the start bit and logic 0 are +6.8V).
The only way that you can tell the difference is by physically looking at the module. The TTL version has the shield extended over the connector as shown in the photo at the top of this page while the RS-232 version does not have this feature as shown in the photo on the right. The documentation only refers to the TTL version and when you are ordering one of these modules you have no idea of what one you are going to receive as the part numbers (EM-408) are the same.
It is incredible that a supplier would create such confusion in the market place and unfortunately their crime is compounded by the dreadful documentation that they supply.
dx.com has a very cheap TTL/RS-232 converter board (link) that you can use to convert from one to the other.
There is also a later version on the market called EM-408E. It looks like the RS-232 version (without the extended shield) but what documentation is supplied claims that its output uses TTL voltage levels. I have not tested this version but it appears to have a few other differences including replacing the enable input with a battery backup input.
Well, according to the link, my GPS is RS-232, and, according to the same link, this's what it says !!: "RS-232 Version Output
If you are connecting this version to a microcontroller you will need to use an interface chip like the MAX232 to convert the output to TTL levels and signaling polarity. An alternative is to clamp the output to +5V/0V using a resistor and diode then invert the serial data stream in software in the microcontroller.". But, is the arduino considered as a microcontroller, and therefore, I'll need the MAX232 ?!!.