Alan Sugarman wrote:
> Is is possible to attach an AIS receiver to the Raymarine C-80 -
>
> What is required to accomplish this?
Money. [grin]

Raymarine makes an AIS receiver that, according the write-up, will do a
number of things that are attractive. But at $1200 MSRP, ouch. IIRC,
Defender is selling the unit at around $975.
>
> May I use a splitter in the cable coming from my mast top antenna?
It's included in the Raymarine unit.

http://www.raymarine.com/raymarine/SubmittedFiles/2007_brochures/AIS250_Brochure_LR.pdf

Having said that, I'm finding the DIY path somewhat challenging
(although, so far, not obviously insurmountable).

Following up in the Milltech Marine link, it seems their SR161 receiver
is a good deal for a "casual" user. It will apparently listen to one of
the two AIS channels (87B and 88B), picking whichever channel has a
better signal (as opposed to using both channels all the time, as the
SR162 does, at a little more than 2x the SR161 cost). However, it
outputs its messages at 38400 baud (AIS standard) while most GPS' and
NMEA devices run at 4800 or 9600. And here's where life gets ugly. I
contacted NoLand Engineering about their multiplexer, which basically
takes input for a number of different NMEA streams and sequences their
transmissions into a readable stream (that is, just combining the wiring
will not work). At this point NoLand doesn't have a "mux" that will
accept the AIS 38400 baud stream along the other streams at 4800 or 9600
baud. Yet - look for one "in a few months".

All is not lost at this point. If you're lucky enough to have a
computer with a lot of separate USB ports, you may be able to let the
computer do the "muxing" (multiplexing) for you. That is, the program
(e.g., Coastal Explorer) takes on the job of accepting data in the
correct order. At least that's the theory. I'm looking into what's
needed to convert that to practice and will report back what I find out.

To summarize the above: for DIY AIS, you need a receiver, you need a
serial port (or serial to USB converter), and you need a program to
display the data (e.g., Coastal Explorer). To integrate this with GPS,
a second serial port (serial to USB converter) is needed for that data.
Add in data from wind, speed, depth instruments, and there must be some
way to multiplex the GPS data stream, instrument data stream, and the
AIS data stream.

VHF splitters... The problem is the VHF antenna is used to receive
signals and transmit signals. The VHF radio will disconnect the
receiver when the transmitter's keyed. But, unless protected, the AIS
(also VHF) receiver will see a 25 watt "shout" on its input - not a good
thing. Additionally, it's not enough to just wire two antenna leads in
parallel or even in series (impedance issues show up). The antenna,
transmitter, and receiver(s) need to see a connection that looks "right"
to them. There are, of course, many ways to do this but a passive (not
using power to run amplifiers, etc - the least complicated and least
expensive solution.) splitter will create some loss in the antenna line,
reducing signal strength coming in and going out. For peak efficiency,
then, two antennas are the way to go. If, however, adding a second VHF
antenna is out of the question for some reason, a splitter will be a
satisfactory solution.

Cheers,
Rick Emerson
¡

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Received on Mon Feb 26 11:19:34 2007