Single GPS antenna, multiple devices

[rogerthebodger]

I meant to say transponder, obviously.

Closer but a transponder responds to a received signal.

A transponder is a wireless communications, monitoring, or control device that picks up and automatically responds to an incoming signal. The term is a contraction of the words transmitter and responder. Transponders can be either passive or active.

A transceiver will send a signal unilaterally (no received signal is needed) and will also receive a signal which normally as done info .

The reception and transmission are asynchronous where as a transponder the signals are synchronous.

Think and aircraft transponder then responds to the reception of a radar scan.

 

[PaulRainbow]

Closer but a transponder responds to a received signal.

A transponder is a wireless communications, monitoring, or control device that picks up and automatically responds to an incoming signal. The term is a contraction of the words transmitter and responder. Transponders can be either passive or active.

A transceiver will send a signal unilaterally (no received signal is needed) and will also receive a signal which normally as done info .

The reception and transmission are asynchronous where as a transponder the signals are synchronous.

Think and aircraft transponder then responds to the reception of a radar scan.

Nice quote from a Google search at this address: What is transponder? - Definition from WhatIs.com

The electronics industry decided that AIS devices that receive and send data should be referred to as "transponders".

Based on your Google quote, their thinking might have been, that it picks of GPS signals and automatically responds to them by by transmitting them, along with some extra data, such as the vessel, name, MMSI etc etc

If you feel that you need to refer to them as transceivers, that's entirely up to you.

 

[TernVI]

An AIS is a transponder in that it transmits data in response to or controlled by a signal it receives from a remote device.
Particularly a Class B, which may be 'polled' by AIUI port control stations and possibly Class A vessels.
Some people in the trade don't regard Class A AIS as a transponder, because it's not directly responding to another unit in the way that an IFF does.
But OTOH, all AIS's have their timing controlled by the cloud of AIS's of which they are a member....
The ITU use 'transponder' in defining Class B IIRC

As technology has moved on, the jargon is still a bit WW2.
Is a mobile phone a transceiver? Transponder? does it matter?

Would an AIS receiver which puts the data onto WiFi be a transponder? Maybe literally yes, but maybe not in a more useful sense....

 

[rogerthebodger]

Nice quote from a Google search at this address: What is transponder? - Definition from WhatIs.com

The electronics industry decided that AIS devices that receive and send data should be referred to as "transponders".

Based on your Google quote, their thinking might have been, that it picks of GPS signals and automatically responds to them by by transmitting them, along with some extra data, such as the vessel, name, MMSI etc etc

If you feel that you need to refer to them as transceivers, that's entirely up to you.

I take your point, but my understanding that an AIS transmits its signal based at regular intervals. The position data more often than the ship static data

The position data is transmitted every few 2 to 10 seconds and the ship static data every 6 minutes.

My understanding is that the data is not sent as a response to any GPS signal but clearly uses the GPS position data to compose the dynamic AIS data.

The reception side looks for a slot to allow the transmitted signal to be send in dead air and to compose the AIS data received from other ships.

My understanding is that a transponder responds to a received scan immediately not on a time individual.

I am being very pedantic and in reality as long as we all understand what we talking about what different people call a device is not really important.

your link What is transponder? - Definition from WhatIs.com uses the exanple of an aircraft poition location and an RFID tag. Both respond to a signal to respond with data.

AIS transceiver don't do that as far as I understand

 

[GHA]

What was the thread about again before the arguments about semantics started?

Can't remember but it was much more interesting.... ?

 

[rogerthebodger]

What was the thread about again before the arguments about semantics started?

Can't remember but it was much more interesting.... ?

Yes it was about GPS antenna connections that I and several answered.

Some posted about connecting GPS antenna to AIS and that when it went off track.

Quite normal these days

 

[GHA]

Quite normal these days

Unfortunately so, some grumps will light the blue touch paper and off goes the thread to bickersville......

 

[AndrewB]

You need a multiplexer to combine two signals from two sources, otherwise you'll end up with garbage. But why would you want to combine two GPS sources anyway?

Yes, but it doesn't matter. Use 1 GPS source to feed into the AIS and the other to feed into the rest. You could get rid of one GPS and use it to feed into everything as the number of devices you are sending the GPS feed to is 4.

Even with a multiplexer I had trouble. My yacht had been set up like this when I bought it. The GPS signals competed, the multiplexer was only retransmitting partial sentences, except perhaps once in 15 minutes a complete sentence would get through to the instruments. So my position, not to mention course, was a bit approximate! Took me a while to catch on, but then easily rectified as you describe.

 

[TernVI]

Even with a multiplexer I had trouble. My yacht had been set up like this when I bought it. The GPS signals competed, the multiplexer was only retransmitting partial sentences, except perhaps once in 15 minutes a complete sentence would get through to the instruments. So my position, not to mention course, was a bit approximate! Took me a while to catch on, but then easily rectified as you describe.

Does not sound like a very good multiplexer.
If you are not going to have decent muxing, then you will only get away with having the bus lightly loaded, a few short sentences at longer intervals.4800 Baud soon fills up and you get clashes.
Combining a 4800 baud stream from a GPS with other data and spitting it out at a much higher bit rate is a safer approach.

I think if you have two GPS sources, you should think through the consequences of them disagreeing about the position.
You don't want a situation where the AIS is getting a bad GPS signal, but you don't notice because the chart plotter has a good signal for instance.

 

[laika]

I think if you have two GPS sources, you should think through the consequences of them disagreeing about the position.

One option would be a multiplexer as AngusMcDoon suggested but you'd need one with some smarts to only allow GPS from your backup source through if the primary went down, otherwise you may end up with your plotter thinking you're jittering backwards and forwards a few metres every second or so. Some of the higher end multiplexers can do this (but are probably prohibitively expensive) or you can go open source with a raspberry pi.

 

[GHA]

Some of the higher end multiplexers can do this (but are probably prohibitively expensive) or you can go open source with a raspberry pi.

Signalk now has preferential source priority though beta so far. Seems to solve a load of issues for people with multiple data sources sending the same messages.

Source Priorities Settings Experimental
Use Source Priorities to filter incoming data so that data from lower priority sources is discarded when there is fresh data from some higher priority source.
Incoming data is not handled if the latest value for a path is from a higher priority source and it is not older than the timeout specified for the source of the incoming data. Timeout for data from unlisted sources is 10 seconds.
You can debug the settings by saving them and activating debug key signalk-server:sourcepriorities in Server Log

 

[laika]

Signalk now has preferential source priority though beta so far. Seems to solve a load of issues for people with multiple data sources sending the same messages.

kplex has had that for ages