AIS Transponder: Yes or No

[David M]

So, does Class A broadcast at greater than 25 watts? I don't think that how often info is broadcasted would have anything to do with the antenna design, would it?

[Auspicious]

Originally Posted by David M

Did Larry or Shawn give a reason for a FA150 (Class A AIS transceiver) requiring a special AIS antenna? Power does not seem to be the reason because VHF antennas are connected to transmitters that are limited to 25 watts....unless Class A is greater than 25 watts? Could that be the reason?

I'd like to give Furuno more than a few minutes to review the write-up I did of our discussion.

Originally Posted by David M

So, does Class A broadcast at greater than 25 watts? I don't think that how often info is broadcasted would have anything to do with the antenna design, would it?

Class B AIS transponders run at 2 watts. I don't recall the power level of Class A but it is lots more (10? 25?).

[David M]

Oh interesting...I bet that's its...power transmission makes the difference in antenna design?

[jeffrobbins]

Class A is 12.5 watts maximum

[CarinaPDX]

Class A transmit power=12W. Normal VHF antennas should work just fine: AIS-tuned might work a little better. If there is a problem getting out there are a number of possible causes. My brand-new (expensive) VHF had a 5:1 SWR out of the box, so don't assume that premium brands don't have quality issues.

Check Wikipedia: Automatic Identification System - Wikipedia, the free encyclopedia

I stand corrected: Class A and B have different position messages. Still, all Class A systems will recognize Class B positions, if not static data.

[CarinaPDX]

Was I really working on the last post for 8 minutes, while jeffrobbins got the answer in?

I must be slowing down...

[Auspicious]

Originally Posted by CarinaPDX

Class A transmit power=12W.

Thanks Jeff. I looked and couldn't find the number, and couldn't remember for sure.

For the rest of your statement I'm feeling a little constrained by my offer to Furuno to review the summary of our phone call.

[S/V Alchemy]

I like threads where I see information in greater detail like this one. Good stuff, guys.

[s/v Jedi]

What I would like to remark is that any VHF antenna that shows VSWR 4:1 at AIS (which is on regular VHF channels/frequencies) should be banned from selling as a marine VHF antenna.

I think I remember that a marine VHF antenna should have a max. VSWR of 2:1 over the complete VHF bandwidth, which should make them all at least suitable for AIS work. A 1.1:1 AIS antenna is of course much better than a 2:1 one (which looses half the power/3dB).

I have noticed big differences between VHF antenna designs too. I switched my main VHF antenna to a di-pole design (instead of standard ground plain design) and get much better range. For most people reading this: renewing your coax cable will probably make a bigger difference than buying a better antenna.

On my mizzen I have a simple VHF stainless whip (Shakespear ground plane) and it works well enough on my class-A AIS.

Last but not least: every coax/antenna installation should be checked with meter and dummy load (connect dummy load at antenna position too). I have seen too many installations where there was either a 100% short or even 100% open connection (asking me: are those connectors supposed to be soldered??!! ouch...)

ciao!
Nick.

[David M]

I found the solderless coax connectors to be junk. I went back to the old fashioned yet more reliable way...soldering.

[s/v Jedi]

Originally Posted by David M

I found the solderless coax connectors to be junk. I went back to the old fashioned yet more reliable way...soldering.

Yes but the problem was that this cruiser used a solder-connector without soldering it... many don't even know that there are two kinds so the solderless connectors get bad rep when stories about connectors that have not been soldered come up... even though those stories are about connectors that are supposed to be soldered.

:-)

cheers,
Nick.

[SailFastTri]

My boatyard used a solderless connector on my masthead -- Inspected it and found the pins hadn't even pierced the insulation fully. I cut it off and soldered on a new one. Now I know its good for the life of the cable.

[s/v Jedi]

Originally Posted by SailFastTri

My boatyard used a solderless connector on my masthead -- Inspected it and found the pins hadn't even pierced the insulation fully. I cut it off and soldered on a new one. Now I know its good for the life of the cable.

Exactly. The thing is that with some practice, it is not too difficult to make good connections with those solderless connectors. Also, without much practice, it's not too difficult to ruin a solder connector by using too much heat which melts the insulation around the inner conductor and creates a full short between the two conductors of the cable.

So it all comes to experience putting these connectors onto cables. And once you get enough experience, you will prefer soldering types unless it's outside in the wind where it's very difficult to make a proper solder connection, in which case you know how to make a proper solderless connection. I hope anybody reading this can follow me :-8

ciao!
Nick.

[jeffrobbins]

Yes, I agree. At the risk of repeating myself.... my experience providing technical support to people installing transponders has taught me that the vast majority of problems are due to antenna connectors. People are quick to jump to the conclusion their transponder isn't working but in the end it often comes to a connector somewhere. Don't overlook old and tired cable too.

[s/v Jedi]

Originally Posted by jeffrobbins

the vast majority of problems are due to antenna connectors. People are quick to jump to the conclusion their transponder isn't working but in the end it often comes to a connector somewhere. Don't overlook old and tired cable too.

I'll take it a step further: it's my experience that at least 50% of the cruisers out here have some sort of problem with coax cables, connectors or antennas. Flip a coin to get the feel for 50%, then make sure you're not in the wrong 50% :-)

ciao!
Nick.