AIS transmitter

[stephen_h]

We have a VHF with AIS reciever which is linked to our chartplotter.

I would like to transmit our position so can I get a transmitter
only or are they all transponders?

 

[Halo]

Never heard of a transmit only system. AFIIK you need to buy an ais system with both a transmit (Tx) and a recieve facility and connect it to an aerial.

 

[Buck Turgidson]

All TX/RX but it doesn't matter you just have redundancy. I can recommend the AMEC 108s. Cheap as chips for combined AIS and splitter and works perfectly.

 

[pvb]

I can recommend the AMEC 108s. Cheap as chips for combined AIS and splitter and works perfectly.

I think the em-trak B100 and splitter is much better value for money at around £465.

 

[PaulRainbow]

I think the em-trak B100 and splitter is much better value for money at around £465.

+1 The Em-trak is a great bit of kit.

 

[Roberto]

If you use CPA alarms and the like, ascertain the receiver can filter its own Mmsi sentences otherwise the alarms become useless.
I find it useful to have both, a receiver on one side and the transceiver on the other: with heavy traffic one has a quick idea of the delays one's position sent to others is subject to.

 

[Matwill]

I just got a boat with a missing VHF, since ill be sailing in and out of the port of Rotterdam I was thinking of getting the new B&G V60-B that has TX/RX built in, does anyone else have experience with this one or is it better to get separate units?

 

[doug748]

I just got a boat with a missing VHF, since ill be sailing in and out of the port of Rotterdam I was thinking of getting the new B&G V60-B that has TX/RX built in, does anyone else have experience with this one or is it better to get separate units?

I think it's maybe too new to find anyone who is using one. There was a similar product announced about 4 or 5 years ago (Standard Horizon? Can't remember) but it never materialised, certainly in the UK. I got fed up waiting and bought a Vesper 850 Watchmate linked to an Icom VHF. This achieves the same thing but needs an extra aerial (not always a bad thing, useful back up) and of course is more effort to set up.

I am not sure what I would do now, the Vesper screen is nice to have but the ease of just dropping in the B & G would be tempting. I see Cactus have the V60B for £900 which would be less than my set up.

 

[Bobc]

Cheapest transponder on the market is Matsutec HA102 at about £200-£250.

 

[Spirit (of Glenans)]

I just got a boat with a missing VHF, since ill be sailing in and out of the port of Rotterdam I was thinking of getting the new B&G V60-B that has TX/RX built in, does anyone else have experience with this one or is it better to get separate units?

While a combined unit has great advantages at the installation stage, I would prefer to have separate units in the event of a breakdown. Also my preference would be for a separate antenna on the pushpit, with its advantages in the event of a rig failure, rather than using a splitter on the masthead antenna, which has its own inherent disadvantages, particularly in a busy area.

 

[rszemeti]

I just got a boat with a missing VHF, since ill be sailing in and out of the port of Rotterdam I was thinking of getting the new B&G V60-B that has TX/RX built in, does anyone else have experience with this one or is it better to get separate units?

You can't get an AIS transmitter without a receiver, they ALL have a receiver as they need to be able to listen for control messages and identify gaps in which they can transmit.

 

[ShinyShoe]

You can't get an AIS transmitter without a receiver, they ALL have a receiver as they need to be able to listen for control messages and identify gaps in which they can transmit.

He means separate from the VHF.

I've never seen anyone explain if there are technical disadvantages to splitters, beyond the risk of tech failure. If you are transmitting a 'big' message on any channel - say taking 20 seconds... Does that mean you don't get any incoming AIS data in that time and no outbound either? If you are doing < 2kts does that mean if it tried to update while you spoke it doesn't know and so sends another update in 3 mins as if all was normal? No impossible you are calling someone then... Now 9 minute update?

Perhaps this is less of an issue than I think.. but my gut feel is a separate antenna would not have these issues...

 

[prv]

He means separate from the VHF.

He knows he needs something separate from the VHF, but I'm pretty sure he was asking about getting something that was purely a transmitter with no receive capability in order to, I don't know, avoid depleting the limited world allocation of radio receiver circuits or something?

I've never seen anyone explain if there are technical disadvantages to splitters, beyond the risk of tech failure.

They inevitably introduce some loss into your transmissions, though hopefully not enough to seriously matter. Newer types claim not to introduce any loss when receiving, though I wonder whether they're truly comparing against the alternative of a single unbroken cable. Even if the circuit doesn't attenuate the signal, the extra connectors surely must do?

Plus as you say, if either unit is transmitting then all three other functions are suspended while it does so.

If you are transmitting a 'big' message on any channel - say taking 20 seconds... Does that mean you don't get any incoming AIS data in that time and no outbound either?

Correct.

If you are doing < 2kts does that mean if it tried to update while you spoke it doesn't know and so sends another update in 3 mins as if all was normal?

That seems very likely.

It might be possible for the AIS transmitter to detect the "closed" splitter as an antenna fault, and if so to retry its transmission sooner. But I suspect the splitter is more likely to try to look like a working antenna to avoid spurious warnings, and I also wouldn't like to bet that a transmitter detecting an antenna fault (which they generally do do) then reacts by rescheduling its next transmission. More likely the transmission rate is fixed and each one either goes out or doesn't.

Perhaps this is less of an issue than I think.. but my gut feel is a separate antenna would not have these issues...

A separate antenna wouldn't have the issues - but I don't think they're very severe issues for most of us in practice.

Pete

 

[Salty John]

"Splitter" is actually an incorrect description of these switching devices. A splitter is a means of dividing the signal over two devices whereas what we want a splitter to do is divert the antenna function from one device to another during receiving and transmission, and to default to the more important of the devices. But everyone calls them splitters, so it's important to check the spec of the "splitter" to be sure it is actually an automatic diverter, not a divider or a simple A-B switch.

 

[Buck Turgidson]

I just got a boat with a missing VHF, since ill be sailing in and out of the port of Rotterdam I was thinking of getting the new B&G V60-B that has TX/RX built in, does anyone else have experience with this one or is it better to get separate units?

I'd jump on that solution every time. The idea that a separate unit gives redundancy I think is a bit of a fallacy as you have the same circuits with fewer connections in a combined unit and therefore less potential failure modes.

My only gripe is the styling which isn't to my taste.

 

[ShinyShoe]

He means separate from the VHF

He knows he needs something separate from the VHF, but I'm pretty sure he was asking about getting something that was purely a transmitter with no receive capability in order to, I don't know, avoid depleting the limited world allocation of radio receiver circuits or something?

I just got a boat with a missing VHF, since ill be sailing in and out of the port of Rotterdam I was thinking of getting the new B&G V60-B that has TX/RX built in, does anyone else have experience with this one or is it better to get separate units?

The OP was asking about Tx only, Matwill was asking about B&G's new eye wateringly expensive V60-B which is a class B Tx and obviously Rx, and standard DSC VHF all in one.

It will still behave much like a set with a splitter, but I guess could be more intelligent and queue transmission if you are busy talking.

It will set you back £1k. That is more than buying a decent DSC VHF, splitter and Class B. It's easier to install. But... If it breaks you may loose everything rather than a £200 component...

 

[rszemeti]

He means separate from the VHF.

Reading back to the original, he did mean a transmit only.

I've never seen anyone explain if there are technical disadvantages to splitters, beyond the risk of tech failure.

The advantage is you only need one aerial, and it is the one very high up, so it improves the performance of the AIS. There are 2 downsides,

1) If the spliter fails, you lose all comms, so best to make sure it is easily bypassable. Get an SO239 coupler to insert in its place and restore your VHF radio.

2) All plitters have a small insertion loss, so you *slightly* degrade the performance of your VHF radio ... some claim to have an amplifier to make up for the loss, but, for reasons I won't go into, it will still result in a slight degradation of performance.

If you are transmitting a 'big' message on any channel - say taking 20 seconds... Does that mean you don't get any incoming AIS data in that time and no outbound either?

That is correct. Even with a separate antenna it is quite likely that you will not be able to receive most AIS transmissions when transmitting at 25W on your main antenna for comms, as the AIS receiver, unless very well designed, will suffer from blocking.

If you are doing < 2kts does that mean if it tried to update while you spoke it doesn't know and so sends another update in 3 mins as if all was normal? No impossible you are calling someone then... Now 9 minute update?

If it is any good, it will detect the high level of RF when you transmit and know not to try sending the message, and know it still needs to be sent at the next available slot. The one I have been messing with knows when there is RF from the main comms radio and won't even try to transmit and the software queues the message.

Perhaps this is less of an issue than I think.. but my gut feel is a separate antenna would not have these issues...

A separate antenna is likely to be mounted low down (eg on the pushpit rail) and will not perform as well. In reallity, that isnt really an issue as AIS target more than a mile or two away are usually not of any concern. AIS transmissions very frequently don't get through to all stations listening, as other stations may transmit on top, so don't worry about transmissions being missed, many many are, and the system is designed to cope. Personally I have a main antenna on top of the mast, and a backup antenna on the pushpit, covers all eventualities.