DIY aerial for AIS - results

[LadyInBed]

I stripped back a measured length of coax and hung it in the saloon as a vertical dipole.
It started picking up ship AIS data at about 2nM. I then grounded the coax screen and increased the range to about 2.5nM, occasionally picked up a ship at 4nM.
I have a fall back option of mounting my spare vhf up the mizzen, but I am not after a huge range.
3 - 4nM would suit, but I can live with 2.5nM as I never do anything about ships at a greater distance.
I now see that they all give me 0.5nM CPA.
Would you be happy with this?

 

[fireball]

nope - because with a 2.5Nm range you're not giving the kit time to pick up the details of the ship to give you a full(er) picture - you can visually see them before getting them on screen - thus AIS data becomes pretty much meaningless unless you use it just to confirm your avoiding techniques ....

with 2 masts I'd definately have an antenna up both ....

 

[lw395]

I would want some margin for the extra loss in heavy rain, when the transmitter is slightly poorly, seagull on Tx antenna, small island between you and ship etc, as well as agreeing with Fireball.
You want 'damn sure range' not typical range imho.
2.5 miles is not far at 25 kts mid channel. 6 minutes! Two of those minutes can be lost in the AIS cycle.
Might as well go the extra to get the full benefit.
A rubber stubby on the pushpit would do better I think.

 

[Bilgediver]

Cutting it a bit fine...a decent whip on the pulpit or better still make a slim jim and put that on the pulpit and it will make a good emergency antenna..Google for slim jim

 

[mhouse]

Why bother with an ariel ?
Ive just got the nasa unit ( Cheap and cheerful I know)
I attached the outer braid to the lower part of the backstay and the middle to the main backstay . In the Thames Estuary I was picking up shipping at 16 miles. A far greater range than using the emergency antenna.
Give it a try . Since you are not transmitting it wont do any harm.

 

[LadyInBed]

I thought about that as an option as that iswhat I use for the FM radio - I will give it a try

 

[LadyInBed]

2.5 miles is not far at 25 kts mid channel. 6 minutes!
Not seen any going at that speed yet. Most seem to be doing around 16 kts.

 

[Elemental]

Maybe I'm being a bit blonde, but could you clarify what you mean by

[ QUOTE ]
I attached the outer braid to the lower part of the backstay and the middle to the main backstay

[/ QUOTE ]

I'm not sure what is the "lower part" and the "main" backstay.

I've been wondering about using the rig as an antenna for my FM stereo..

Thanks, Mark

 

[LadyInBed]

It just gives a large loop.
Receivers are not too fussy about having a aerial cut to a specified length.

 

[fireball]

sounds interesting - would be interested in the results as essentially we could do away with the seperate antenna for the AIS and just use the rigging instead! /forums/images/graemlins/smile.gif

 

[Elemental]

OK, so could I just run the FM antenna coax to, say, the port chainplate, connect the braid, then connect the centre coax core to a wire, which goes around the cabin to the starboard chainplate... or would the electrical connectivity not be good enough through the turnbuckles etc. In which case, how would I connect the coax to the shrouds... /forums/images/graemlins/confused.gif

 

[LadyInBed]

Golly Gosh Sir! you have it.
Don't confuse electrical resistance with impedance at RF.
And in the words of those Radio pioneers - try it and see /forums/images/graemlins/wink.gif

 

[mhouse]

Mark.

(I'm not sure what is the "lower part" and the "main" backstay)

I have an adjustable backstay with a tufnol block 1.5m from deck level. The centre coax is attached to the upper part . Waterproofing is inportant as moisture will easily track back down the wire.