AIS splitter question

Sea-Fever

Sea-Fever

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Would appreciate any learned opinion on this....

AIS splinters range from cheap to pricey, most active, a few apparently passive.

I have seen one device, from Comar, listed on ebay as an "AIS receive splitter".

My question....do you think/believe/know AIS transponders need a different spec splitter compared to AIS receivers??

Perhaps the electronics to guard your VHF from the transponder transmit power output necessitates a pricier splitter.....but how to tell the difference???

Thanks.
 
You need a different spec for receive to transmit. A transmit one will do receive but not the other way about. Its to do with power handling. 25W on transmit, but infinitesimal for receive only.
 
Ok so I've done that classic thing where I post a question and then actually properly try to find out a bit more about it....

Turns out that SOME ads do indeed specify whether an item is suitable for both transmit and receive, but for others the blurb is silent on the issue.....

I suppose I should play it safe and get one that specifically states it is suitable for a transponder. The issue is that for the price of a quality transponder splitter I might just as well mount a new dedicated antenna on the mizzen and gain a back up VHF aerial in the process.
 
MM5AHO said:
You need a different spec for receive to transmit. A transmit one will do receive but not the other way about. Its to do with power handling. 25W on transmit, but infinitesimal for receive only.
Click to expand...

I think the AIS transmit power is less than that but I know what you mean.
 
A splitter which is suitable for AIS transmit will definitely be active rather than passive .... but I suspect that not all active splitters will be suitable for transmission so you do need to read the specs and, if it doesn't say that it is suitable for AIS transmission, then assume that it isn't.

Richard
 
Another option for probably the same cost is to use a second non mast mounted stubby aerial for the AIS. Advantage is that if you lose the main aerial location, you have a spare for emergencies and you are not compromising the main VHF system. That’s what I have done and despite the AIS being on the push pit I still get signals from 20+ mm away.

Just a thought.
 
But the radio is still going through the splitter at 25W, I didn’t both with a splitter and have antenna on pushpit, works just as needed
 
RichardS said:
A splitter which is suitable for AIS transmit will definitely be active rather than passive .... but I suspect that not all active splitters will be suitable for transmission so you do need to read the specs and, if it doesn't say that it is suitable for AIS transmission, then assume that it isn't.

Richard
Click to expand...

Safe option I guess.
 
ctva said:
Another option for probably the same cost is to use a second non mast mounted stubby aerial for the AIS. Advantage is that if you lose the main aerial location, you have a spare for emergencies and you are not compromising the main VHF system. That’s what I have done and despite the AIS being on the push pit I still get signals from 20+ mm away.

Just a thought.
Click to expand...

Hmmm I'm not sure 20 millimetres is anything to be proud of.

Although if you meant 20 nautical miles that is indeed quite good. Is that receive only? I wonder what that mounting location does for transmission range.
 
+1 for ctva's suggestion. My tight-arse home-made diy antenna (cost me about A$20 to make), which I use for AIS on the pushpit works well - best result is about 20nm. I also use it for VHF send/receive occasionally just to prove it works. I have an AIS receiver, no transmit.

I have found that AIS best reception (whether from mast-head or pushpit) results from a combination of: flat water (antenna not wobbling around hence spending more time in best signal plane), clear day (no attenuation by fog/rain), and the target a big ship with a high-mounted antenna. Take away any of these and the range reduces. Power boats with lowish antennas often aren't detected until within a few nm. This might be a hassle if they are belting along, with largish delays in their Class B position.

Cheers, Graeme
 
Sea-Fever said:
Hmmm I'm not sure 20 millimetres is anything to be proud of.

Although if you meant 20 nautical miles that is indeed quite good. Is that receive only? I wonder what that mounting location does for transmission range.
Click to expand...
:rolleyes: I hate auto correct!

I can only say for receive as I’ve never asked anyone about my signal but should be similar.
 
The only way I have checked my AIS transmission is to look up my boat on marinetraffic on the interweb.
My track on that is often lost inland from the Humbet bridge.
 
I have never had great success with splitters. I would recomend putting a dedicated AIS antenna on the pushpit.
 
VHF range is a combination of your radio horizon and the co-respondents radio horizon. Your radio horizon is 1.4 x root of height above sea level in feet, answer is in nm. A 49' mast mount gives a horizon of 7 x 1.4, so about 10 miles. To this you add the other stations radio horizon to get range. An identical boat could communicate at 20 miles. A Coastguard station high on a headland would have a radio horizon of, maybe, 50 nm, so could communicate with our example boat at 60 miles.
These ranges are theoretical and often enhanced by atmospheric conditions - ranges of several hundred miles have been noted at times.
Assumes, of course, your radio, AIS, cable and antenna are in good working order.
 
Thanks Saltyjohn....

Do you have any opinion on required separation between dedicated vhf and ais antennas on the same mast.. .could I use a standoff to provide that separation?

Slight thread drift on my own thread.. .I know.
 
Many people say 1m separation. I have a lot of anecdotal evidence to suggest half that is OK. In theory, a quarter wavelength, just under 500mm is the minimum. Two typical stand-off brackets on either side of a 160mm wide mast gives you 500mm.
Of course, both antennas at the masthead doesn't help in a dismasting - one on the deck and one up the mast provides for that emergency. Range is less critical for AIS so I'd always put that at the lower level.
 
Salty John said:
Many people say 1m separation. I have a lot of anecdotal evidence to suggest half that is OK. In theory, a quarter wavelength, just under 500mm is the minimum. Two typical stand-off brackets on either side of a 160mm wide mast gives you 500mm.
Of course, both antennas at the masthead doesn't help in a dismasting - one on the deck and one up the mast provides for that emergency. Range is less critical for AIS so I'd always put that at the lower level.
Click to expand...

Many thanks John. Now all I need to do is find is a friendly knowledgeable person who sells antenna stuff online....
 
When I bought my AIS transceiver from Digital Yacht a few years back, they recommended a pushpit mounted aerial rather than a splitter although they supplied both.

I am not sure what range you are looking for, but I can pick up the big ships in Southampton from my berth in Haslar Marina Portsmouth.
 
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