Page 5 of this manual also discusses the NMEA-0183 to PC interface

http://www.autonnic.com/autonnic/Autonnic.nsf/0/2859F4421DBFF9A18025713A004B1A38/$file/A5020%20manual%2003.pdf#search=%22nmea%200183%20rs 232%20converter%22

Here's a level converter for NMEA-0183 to RS232:

http://www.cruzpro.com/nc20.html

Here's another interesting link about NMEA-0183/PC:

http://www.marinelektronik.se/faq.htm

They say:

NMEA is not the same as RS232. The voltage levels are different, which can
cause data transmitted by
the computer's serial port not to be understood by the receiving equipment,
and also for the PC either
not to understand the incoming NMEA sentences, or in some cases for the PC's
serial port to be damaged.
In addition, NMEA 0183 is designed to protect devices and to minimize
interference problems
by having the data input opto-isolated (further interference protection is
provided by specifying the use
of shielded twisted pair cabling). For this reason, we strongly recommend
the use of an NMEA/RS232 converter.

NMEA 0183 compatability does not guarantee that systems can talk to each
other.
There are many sentences available, so the same data can be transmitted in
many different ways.
Also, within a sentence, not all of the data fields need to be filled in, so
you cannot always check
compatability by looking at the lists of sentences transmitted/received.
In some cases a NMEA 0183 sentence filter is necessary to establish
compatability.

Because of the difference in signal levels between NMEA and RS232C we
recommend
the use of a NMEA/RS232C interface. If the computer is powered by the ships
AC
outlet you will need an isolated type of interface to avoid ground voltages.

More he

http://www.caracolyachts.com/t_pcintfc.htm

When wiring an NMEA device to an RS-232 device, be aware that you are wiring
together devices which use a different electrical specification. So if on a
device you have a choice of an NMEA port or a RS-232 port, choose to match
if possible NMEA to NMEA or RS-232 with RS-232.

However almost invariably an RS-232 device can be connected to an NMEA
device and vice versa. There are two potential problems, firstly the RS-232
and NMEA specifications use different voltage levels. This is seldom a
problem, except on very old devices.

The biggest potential problem is that NMEA is a differential signal, with
the Transmit and Receive pairs, and RS-232 signals are referenced to a
common ground.

When wiring an NMEA device to provide input to an RS-232 device, connect the
Transmit + of the NMEA device to the Receive of the RS-232 device, and the
Transmit - of the NMEA device to the RS232 signal ground.

When wiring an NMEA device to take input from an RS-232 device, connect the
Receive + of the NMEA device to the Transmit of the RS-232 device, and the
Receive - of the NMEA device to the RS232 signal ground.

When wiring an NMEA device to both provide input to and take input from an
RS-232 device, connect the Transmit + of the NMEA device to the Receive of
the RS-232 device, connect the Receive + of the NMEA device to the Transmit
of the RS-232 device, and the Transmit - of the NMEA device AND the
Receive - of the NMEA device to the RS232 signal ground.

In some instances tying the Transmit- and Receive - of the NMEA port
together can cause problems. In this case you need to use an NMEA to RS-232
converter between the two devices. We find this to be a requirement in less
than 1% of cases, but should be borne in mind if you are experiencing
problems.

Modern Furuno radars almost always require this type of converter.

http://www.euronav.co.uk/Products/Ha...EAProducts.htm

Most personal computers communicate with the outside world via a protocol
called RS232. NMEA and RS232 operate on slightly differing signal voltage
levels and with some older equipment there is a danger of unreliable
communication and possible damage to the computer serial port unless a
suitable interface cable is used. Some GPS manufacturers supply suitable
cables with their devices - if you have one of these, do check that it is
fully opto-isolated and that it protects against reverse polarity before
using it.

http://web.inter.nl.net/hcc/van.het....center/pcc.htm

It is possible to use a simple home-made connection cable to connect the
instrument's NMEA port directly to the PC's RS-232 com port, but it is
strongly recommended to use a NMEA to RS 232 converter instead. You will
find more information regarding this is in the manual file (MANUAL.TXT) of
the program.


http://www.actisense.com/HTML/Produc...r%202/FAQs.htm

This adapter cable also converts the RS422 / RS485 (NMEA) voltage levels to
RS232 (PC) voltage levels, and vice-versa.


http://www.epa.gov/glnpo/image/vbig/221.jpg

http://mishami.image.pbase.com/u11/l...._STA50032.jpg

http://www.frenchcreekboatsales.com/...ccaneer_01.jpg