Si - Tex Metadata Class B AIS Transceiver

[Pete7]

Originally Posted by transmitterdan

It has external GPS antenna.

I am pretty sure it has an internal GPS with an external antenna if necessary. I will give it a try next time I am down the boat at the weekend.

Pete

[s/v Jedi]

Originally Posted by transmitterdan

It has external GPS antenna.

Indeed. Approved AIS transponders don’t have internal antennas

[gamayun]

Originally Posted by s/v Jedi

Indeed. Approved AIS transponders don’t have internal antennas

So this made me go hmmm because the Vesper unit and others that I have been looking at have internal GPS units. Maybe the light bulb just went off. I'm guessing the internal GPS is fine for receive AIS but it must have an external GPS to transmit properly. Could this have something to do with the strength of the RF signal that would be transmitted every few seconds right near my berth?

[Pete7]

Ok thanks, I stand corrected.

Pete

[daletournier]

Originally Posted by gamayun

So this made me go hmmm because the Vesper unit and others that I have been looking at have internal GPS units. Maybe the light bulb just went off. I'm guessing the internal GPS is fine for receive AIS but it must have an external GPS to transmit properly. Could this have something to do with the strength of the RF signal that would be transmitted every few seconds right near my berth?

On Freeform (freedom) I had the vesper 850 with internal gps, I couldn't get it to work, I had to add a external gps that was next to it in the cabin it then worked great?

I have the xb8000 vesper on Sukha which comes with a external gps.

[s/v Jedi]

Originally Posted by gamayun

So this made me go hmmm because the Vesper unit and others that I have been looking at have internal GPS units. Maybe the light bulb just went off. I'm guessing the internal GPS is fine for receive AIS but it must have an external GPS to transmit properly. Could this have something to do with the strength of the RF signal that would be transmitted every few seconds right near my berth?

Internal GPS (receiver) yes, but they come with an external GPS antenna. An active GPS antenna is the actual antenna with a RF pre-amplifier which takes care of any coax cable losses. An “external GPS” is both receiver and antenna which is not allowed for transponders. AIS receivers have no GPS at all.

I have heard of units with internal antenna but never actually encountered one.

[Pete7]

Originally Posted by gamayun

So this made me go hmmm because the Vesper unit and others that I have been looking at have internal GPS units. Maybe the light bulb just went off. I'm guessing the internal GPS is fine for receive AIS but it must have an external GPS to transmit properly. Could this have something to do with the strength of the RF signal that would be transmitted every few seconds right near my berth?

I read the bit in blue slightly differently.

The transmission goes out via the VHF antenna, not the GPS antenna.

Pete

[daletournier]

Originally Posted by Pete7

I read the bit in blue slightly differently.

The transmission goes out via the VHF antenna, not the GPS antenna.

Pete

Yes, glad you said that, I was thinking the same.

[Kelkara]

Originally Posted by s/v Jedi

neither the Vesper 6000 and the 8000 have internal antennas.

The XB6000 has an internal antenna.

The XB-6000 has its own internal GPS antenna and a powerful external GPS antenna is included if it needs to be mounted where there is no clear view of the sky.

What is not permitted for a class B tranceiver, that is permitted for a receive only device, is to get GPS information from another device. It must be fitted with its own internal GPS receiver.

[gamayun]

Originally Posted by Pete7

I read the bit in blue slightly differently.

The transmission goes out via the VHF antenna, not the GPS antenna.

Pete

Oh duh, I'm mixing antennae. Not unlike my metaphors.

[Pete7]

Originally Posted by Kelkara

The XB6000 has an internal antenna.

Looks like the Em Trak also has an internal antenna making the external one optional. From the Em Trak website:

The B350 is small and entirely water and weather proof and comes with an integrated high-performance GPS antenna making an external antenna optional in most installations and providing complete installation flexibility and convenience.

[s/v Jedi]

Yes, the B350 as well as the Vesper 6000 have internal antennas. The B100 and Vesper 8000 do not so it requires study to find out. The Vesper 8000 was advertised as a 6000 with wifi but it seems they removed the GPS antenna... or maybe the 6000 was updated to have the antenna later on.

For most fiberglass boats an internal antenna works good enough. It’s important to check for obstruction of the sky when heeled. It’s easy to have a solar panel obstruct when heeled etc.

An AIS receiver has no GPS receiver and does not need/use a GPS receiver. It just receives the AIS transmissions and sends them onto the nmea network. Each AIS target includes their position in the transmission.

[Kelkara]

Originally Posted by s/v Jedi

An AIS receiver has no GPS receiver and does not need/use a GPS receiver. It just receives the AIS transmissions and sends them onto the nmea network. Each AIS target includes their position in the transmission.

True if it's just passing AIS data to a chartplotter, but if it has it's own graphical display or calculates CPA, then it needs the boats own position too ... either from an internal or external GPS signal.

[s/v Jedi]

Originally Posted by Kelkara

True if it's just passing AIS data to a chartplotter, but if it has it's own graphical display or calculates CPA, then it needs the boats own position too ... either from an internal or external GPS signal.

Yes, there used to be receiver models with display (NASA etc.). I believe all current models are black box units. It is the display unit (plotter, specialized display unit, computer, iPad etc.) that combines AIS data with own ship position. The AIS nmea messages do not include things like CPA, TCPA etc.; they are all local, calculated data fields.

[GRIT]

Old thread, worth reviving...

My Emtrak AIS has crapped out again. It's not sending out a signal, and it's not been reliable from the start.

I'm looking for a Sotdma transceiver (5w), preferably with a built in splitter. I have a dedicated antenna for the ais on the stern, but the range is not to my liking.

I found the Si-Tex Si-tex MDA-5H transceiver with splitter interesting. Any comments on that one?

I'm not interested in any of the Vesper or Emtrak products, but anything else that works well, and works with nmea2000 would be considered.

Cheers.
Paul.