AIS signals not being received - antenna issues?

[Babylon]

I have just fitted a SH GX2100 VHF with integral AIS. VHF works normally, transmits and receives, and takes Lat-Long from GPS. But AIS doesn't work at all: not only doesn't the screen display AIS targets, but when tuned to Channels 87 and 88 the AIS 'clicks' cannot be heard.

Does this indicate a problem with the unit or the antenna? The antenna is a stub unit fitted atop the mast (circa 2009), rather than the usual longer whip antenna fitted to yachts. But if we can receive voice transmissions clear as daylight and from a good distance, why cannot we hear the AIS clicks? BTW, we've already checked the coax to VHF connector, which is working fine.

Any ideas?

 

[maby]

Sounds more like either a fault on the unit or incorrect configuration - AIS works on the same range of frequencies as voice communications, so an antenna fault which disables AIS but leaves voice working is pretty improbable. If the boat is in the Solent - as your signature line suggests - you should be swamped with AIS hits - even if your antenna was in a very poor state.

 

[Babylon]

Yes, that seems to be the inexorable conclusion, which SH agree with.

There's no configuration meant to be done on the unit at all - just switch it on and should start showing targets.

They'll have the unit back under warranty to sort it out.

 

[l'escargot]

What range have you set the AIS display on? It can be 0.5 to 15 Nm. Are there AIS targets in range?

 

[Babylon]

Tried all ranges. Lots of targets of all types all over Solent, some close some middle distance - all showed on internet app.

 

[LadyInBed]

Tried all ranges. Lots of targets of all types all over Solent, some close some middle distance - all showed on internet app.

Double check setup options, if ok send it back.

 

[nigelmercier]

I'm not 100% sure on this, but I have a feeling the GPS has to be locked before it will display a target.

 

[Martin_J]

Nigel

I did wonder that, but at the time Babylon's VHF was connected to a chart plotter with GPS that was locked on.

At the time, the radio displayed the latitude, longitude and time (as per the plotter) and the small satellite symbol at top left of the VHF display was solid. When we changed the time zone to Summer Time Corrected on the plotter, the radio changed it's display to match.

When powered on, the VHF did transmit a small data sentence to the Plotter at 38400 baud (as seen in the plotter serial line log), seeming to confirm that the radio AIS output was connected correctly to the Chart plotter AIS input.

We expected to hear (as on other radios) the AIS clicks on VHF channels 87 and 88.

The clicks are clear on my SH GX1500E... Wondered if the GX2100 AIS model supresses the audio (and the 'busy' light) on those channels but that would be odd.

 

[l'escargot]

...When powered on, the VHF did transmit a small data sentence to the Plotter at 38400 baud (as seen in the plotter serial line log), seeming to confirm that the radio AIS output was connected correctly to the Chart plotter AIS input...

That could be your problem. The output baud needs to be 4800 and you need to install the supplied inline resistor to achieve this. I had to do that when I recently installed one of these. See here http://www.ybw.com/forums/showthrea...king-to-a-Standard-Horizon-GX2100e&highlight=

 

[Martin_J]

l'Eascargot - Looks like you pointed me back to an answer I previously gave to someone else!

Thank you for reading and replying... keep thinking!

That resistor solution though was to control the NMEA data rate output 'from' the Garmin plotter... to limit it to 4800 as opposed to the default output of 38400 'from' the Garmin.

The 38400 that I refer to (in Babylon's case) is the speed of the data 'from' the AIS VHF 'to' the chart plotter in order to display AIS targets on the plotter.

This AIS output on the VHF is 38400 baud and the plotter when set to receive AIS data will automatically set it's receive speed to 38400. A valid sentence was seen on the plotter at power on of the VHF (on the plotter port that has been set to AIS 38400).

It was the type of sentence that an AIS chip produces on boot up but I can't for the life of me remember the exact format.

What is odd is that the VHF showed no targets on it's screen. Until it recognises targets and displays them on it's screen then we'd not expect it to forward any data.

There does not seem to be an option on the radio to display AIS sentences received..

 

[prv]

That could be your problem. The output baud needs to be 4800 and you need to install the supplied inline resistor to achieve this.

Two red herrings in one sentence!

1) The post you're responding to is about AIS data from the VHF to the plotter. 38400 is correct for this. You're thinking of position data from a GPS to the VHF.
2) The resistor as a means of specifying baud rate is specific to the particular GPS in your thread (and maybe close relations), because it doesn't have a display or buttons to control it any other way. Quite a nifty trick, but wildly irrelevant to any of the devices in this thread.

Pete

 

[nigelmercier]

Two red herrings in one sentence!

No, three. This is nothing to do with the connection.

 

[Martin_J]

The thing that baffled me was that Babylon's GX2100 did not appear to produce the audible clicks when listening on 87/88 (whatever the squelch was set to).

I know a usual VHF radio will but with built-in AIS electrickery this VHF is not the 'usual'.

So - does anyone know if this model suppresses the sounds (since it knows they are AIS)?

SWR on the Antenna/cable setup was <1.25 (so resonant for the frequency).

 

[l'escargot]

Two red herrings in one sentence!

1) The post you're responding to is about AIS data from the VHF to the plotter. 38400 is correct for this. You're thinking of position data from a GPS to the VHF.
2) The resistor as a means of specifying baud rate is specific to the particular GPS in your thread (and maybe close relations), because it doesn't have a display or buttons to control it any other way. Quite a nifty trick, but wildly irrelevant to any of the devices in this thread.

Pete

I'll have to bow to your superior knowledge on that one - particularly knowing the type of GPS input which I can't see in the previous posts.

I look forward to reading your solution to the OPs problem...

 

[l'escargot]

The thing that baffled me was that Babylon's GX2100 did not appear to produce the audible clicks when listening on 87/88 (whatever the squelch was set to).

I know a usual VHF radio will but with built-in AIS electrickery this VHF is not the 'usual'.

So - does anyone know if this model suppresses the sounds (since it knows they are AIS)?

SWR on the Antenna/cable setup was <1.25 (so resonant for the frequency).

I've switched my GX2100 on this morning and there are no audible clicks on either 87 or 88 - it is picking up AIS signals. I have also tried my SH handheld and can't hear them on there either. But I switched on an old XM handheld and they are there. Which would seem to suggest that SH sets filter/suppress them.

 

[Martin_J]

Strange.. My SH GX1500E with a masthead antenna clearly shows BUSY and you hear the tones for each AIS packet received..

 

[l'escargot]

Any solution to this yet?

 

[Tintin]

Ais will only be displayed if a gps signal is present. You dont need a high speed nmea output / input for gps nmea 0183. I am unfamiliar with this radio but my money would be on it not getting the right gps data.

Does it require a dedicated gps aerial? My ais transmitter does.

 

[Martin_J]

The OP said - "and takes Lat-Long from GPS."

I confirmed that the radio in question does indeed receive position information (and time) from an NMEA connected GPS.

 

[Martin_J]

Does it require a dedicated gps aerial? My ais transmitter does.

An AIS transmitter does as you say require a dedicated GPS antenna but this does not refer to an AIS transmitter.

This radio is receiving the lat/long/time information via the usual NMEA 0183 at 4800 baud from the CP300.