It would seem an easy task of the receiver designer to output data sentences
with just the header information when no transmitter is in range. Really
though, I would blame the Raymarine implementation. When you run AIS in
various PC charting software, you either see targets or not. No red X's, no
problems.

"Tapio Sokura" wrote in message
. ..
sw wrote:
Thanks for the info. It's too bad in a way that you get the red X even
though the AIS receiver is hooked up and running. It strikes me as
confusing. My guess is that there will be improvements in the software
down
the road.

The problem is that when no AIS transmitters are in range, the AIS
receiver isn't receiving anything and thus it doesn't output anything on
its serial port. This means that the device on the other end of the AIS
serial cable has no way of knowing whether there simply is no AIS
traffic within range or whether the cable is cut, or if the receiver is
malfunctioning. There is no "keepalive" so that the AIS receiver could
tell serial port listeners that it is still alive and kicking.

Tapio

I should think the alarm be configable on raymarine, but otherwise the
"no ais" status is fine. Having the receive send a keep alive message
isn't very helpful, without an AIS transmitter somewhere how does the
AIS receiver know everything is good? It's not like radar or gps, which
the other status's were designed around, where their is always a
transmitter to listen too.

In any event, in a year or two there will be enough AIS traffic, you
won't be able to get away from it.


sw wrote:
It would seem an easy task of the receiver designer to output data sentences
with just the header information when no transmitter is in range. Really
though, I would blame the Raymarine implementation. When you run AIS in
various PC charting software, you either see targets or not. No red X's, no
problems.

"Tapio Sokura" wrote in message
. ..
sw wrote:
Thanks for the info. It's too bad in a way that you get the red X even
though the AIS receiver is hooked up and running. It strikes me as
confusing. My guess is that there will be improvements in the software
down
the road.

The problem is that when no AIS transmitters are in range, the AIS
receiver isn't receiving anything and thus it doesn't output anything on
its serial port. This means that the device on the other end of the AIS
serial cable has no way of knowing whether there simply is no AIS
traffic within range or whether the cable is cut, or if the receiver is
malfunctioning. There is no "keepalive" so that the AIS receiver could
tell serial port listeners that it is still alive and kicking.

Tapio

What is the brand of your AIS receiver? I have a Milltech AIS SR161,
this unit has 2 leds which indicates if it is receiving signal from
other ships and the other leds indicates when it is sending nmea data
to your plotter.

If you have the old Nasa ais black box without the leds, you have
these problems on not knowing waht is happening


Pascal



b393capt escreveu:

I should think the alarm be configable on raymarine, but otherwise the
"no ais" status is fine. Having the receive send a keep alive message
isn't very helpful, without an AIS transmitter somewhere how does the
AIS receiver know everything is good? It's not like radar or gps, which
the other status's were designed around, where their is always a
transmitter to listen too.

In any event, in a year or two there will be enough AIS traffic, you
won't be able to get away from it.


sw wrote:
It would seem an easy task of the receiver designer to output data sentences
with just the header information when no transmitter is in range. Really
though, I would blame the Raymarine implementation. When you run AIS in
various PC charting software, you either see targets or not. No red X's, no
problems.

"Tapio Sokura" wrote in message
. ..
sw wrote:
Thanks for the info. It's too bad in a way that you get the red X even
though the AIS receiver is hooked up and running. It strikes me as
confusing. My guess is that there will be improvements in the software
down
the road.

The problem is that when no AIS transmitters are in range, the AIS
receiver isn't receiving anything and thus it doesn't output anything on
its serial port. This means that the device on the other end of the AIS
serial cable has no way of knowing whether there simply is no AIS
traffic within range or whether the cable is cut, or if the receiver is
malfunctioning. There is no "keepalive" so that the AIS receiver could
tell serial port listeners that it is still alive and kicking.

Tapio

I looked at the NASA unit, but also ended up buying the SR162.

We are using the Milltech AIS SR162, with the smart antenna splitter. The
splitter makes me nervous however. If it has a fault or blows it's fuse, the
VHF xmit will probably damage the AIS receiver. There is no indicator lamp
on the splitter so you really can't tell what's up....
I wonder what the signal loss is through the splitter?


"Jeremy" wrote in message
ups.com...
I looked at the NASA unit, but also ended up buying the SR162.

sw wrote:
It would seem an easy task of the receiver designer to output data sentences
with just the header information when no transmitter is in range. Really
though, I would blame the Raymarine implementation. When you run AIS in
various PC charting software, you either see targets or not. No red X's, no
problems.

I can see the logic in Raymarine software here, as there are two
possible scenarios: a) there is no AIS traffic in range or b) something
is broken with the AIS receiver setup. Situation a) is normal, but
situation b) needs to be looked at. There's no way an AIS serial stream
listener can deduce which one is the case, so to err on the side of
caution, an alarm is raised. Of course if you cry wolf too often you
might end up in trouble anyway..

Tapio