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Old 21-01-2012, 14:39   #1
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Receiving AIS Signal ?

Hi All,

First time poster so please be kind.

I'm just starting to get interested in AIS and boat/ship monitoring and just want to get an opinion on how I'll go in my circumstances.

Just a bit of background first. I live in Chatswood which is a suburb of Sydney Australia. Chatswood is a built up area and my particular location is in an apartment building which is surrounded by office and residential buildings as you can see from the photo below. Trying to listen to marine chatter on my scanner isn't overly successful however my antenna is most likely the culprit there. I also monitor ADS-B (aircraft) using a dedicated 1090Mhz antenna located on my balcony railing which is successful. I can easily pick up aircraft several hundred kms away however most of my signal for aircraft is due to reflection off of the office buildings I believe.

What I'm trying to work out is whether I'll be able to pick up any AIS signals in my circumstances.

As you can see from the below photo, I have a view of office buildings. However the direction is technically facing a portion of Sydney Harbour and the ocean eg. I'm not facing inland.

According to my research I'm 5kms away from Sydney Harbour to my right. I'm also 10kms away from the Ocean straight ahead as per the arrows shown in the photo. I'm also around 100m above sea level (being on the 18th floor of my apartment building).

I'm also about to get this 3 ft AIS Marine Antenna (236-SW) - 3dB Gain antenna which I am going to mount on the railing about 2 feet away from my ADS-B antenna.

So with this information, how successful do you think I'll be in picking anything up?
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Old 21-01-2012, 14:47   #2
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Re: Receiving AIS signal?

It will be challenging given the distance and that you are shadowed by buildings. At that frequency RF bends some and at 25 watts would definitely carry that distance if it were line of sight. I think you might get some reception sometimes but definitely not good reception all the time. But as you said, you might get some good reflectance off the buildings. I'm just guessing of course. The only way to truly tell is to try. You can always return the antenna and the AIS receiver if it does not work out for you.

Another option is to get onto an AIS website like this one. http://www.marinetraffic.com/ais/ I know that is not quite as much fun though. It is not quite real time like real AIS is.
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Old 21-01-2012, 15:01   #3
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Quote:
Originally Posted by David M
It will be challenging given the distance and that you are shadowed by buildings. At that frequency RF bends some and at 25 watts would definitely carry that distance if it were line of sight. I think you might get some reception sometimes but definitely not good reception all the time. But as you said, you might get some good reflectance off the buildings. I'm just guessing of course. The only way to truly tell is to try. You can always return the antenna and the AIS receiver if it does not work out for you.

Another option is to get onto an AIS website like this one. http://www.marinetraffic.com/ais/ I know that is not quite as much fun though. It is not quite real time like real AIS is.
Thanks for the quick response Dave.

I guess I'll just have to hope for the best. I was pleasantly surprised to pick up aircraft the way I can even if it's not optimal. I'll be happy with similar results for AIS but I'll see how it goes.

I should hopefully get the the antenna sometime in the next week so I'll report back with my success.

Geoff
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Old 21-01-2012, 15:29   #4
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Re: Receiving AIS signal?

Breaking down the ABCs of AIS

It's a line of sight reception and
Quote:
since AIS uses the same frequencies as marine VHF, it has similar radio reception capabilities. Proper antenna installation is important, with a higher antenna typically providing a greater reception area. Class A-equipped vessels, with their higher transmit power and higher antenna installation, reportedly experience 20- to 30-mile reception, while Class B AIS reception is around 5 to 10 miles.
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Old 21-01-2012, 16:05   #5
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Re: Receiving AIS signal?

It appears someone is uploading live AIS from your area to MarineTraffic.com.

Live Ships Map - AIS - Vessel Traffic and Positions

Why would you invest in your own receiver? It would be the same data.
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Old 21-01-2012, 16:10   #6
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Re: Receiving AIS signal?

Quote:
Originally Posted by DotDun View Post
It appears someone is uploading live AIS from your area to MarineTraffic.com.

Live Ships Map - AIS - Vessel Traffic and Positions

Why would you invest in your own receiver? It would be the same data.
Because it's fun!

Also, ultimately I want to utilise the data I receive on my own website. For example with the ADS-B that I receive, I've parsed the received data and created a website displaying real time aircraft movements in my area (see my sig).

I love decoding things myself and then writing software/websites that utilise the data in various ways. While looking at other sites is also fun, nothing beats doing it yourself.
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Old 21-01-2012, 16:12   #7
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Re: Receiving AIS signal?

Quote:
Originally Posted by delmarrey View Post
Breaking down the ABCs of AIS

It's a line of sight reception and
Thanks for the info.. I'm hoping the antenna I have is the problem then.. I suspect I'll have problems due to location but I guess it's a gamble worth taking.. it paid off with the ADS-B monitoring. If worst comes to worst, I'll have to observe from other people's sites.

Cheers
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Old 21-01-2012, 16:25   #8
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Re: Receiving AIS signal?

Just an update to this.. I just sat listening to silence for the last 20 minutes because I forgot to turn off the scanner while scanning 156-157Mhz using a marine antenna I bought a few weeks ago. Up until now I've never been able to pick anything up however, I just a little chatter between marine rescue Port Jackson (probably from a repeater), and it was crystal clear.

I have several possible scenarios.

1. It's very quiet chatter wise on Sydney Harbour.

2. What I just received was indeed just a repeater since I couldn't hear the craft.

Do all AIS signals get repeated by basestations/repeaters or are they only repeated on occasion? I'm starting to think I may receive some signal after all after that transmission.. although it's very silent at the moment.
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Old 21-01-2012, 16:29   #9
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Re: Receiving AIS signal?

AIS uses the high side of the duplex from two VHF radio "channels" 87B and 88B.

Channel A 161.975Mhz (87B)
Channel B 162.025Mhz (88B)
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Old 21-01-2012, 16:31   #10
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Re: Receiving AIS signal?

It's still early on Sunday. Wait until afternoon.
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Old 21-01-2012, 16:31   #11
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Re: Receiving AIS signal?

Quote:
Originally Posted by DotDun View Post
AIS uses the high side of the duplex from two VHF radio "channels" 87B and 88B.

Channel A 161.975Mhz (87B)
Channel B 162.025Mhz (88B)
Yep.. and the antenna i'm getting is tuned for that. I guess time will tell whether I can pick anything up.
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Old 21-01-2012, 16:32   #12
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Re: Receiving AIS signal?

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Originally Posted by delmarrey View Post
It's still early on Sunday. Wait until afternoon.
It's 10:30am.. I would have thought it'd be busy on the harbour
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Old 21-01-2012, 16:37   #13
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Re: Receiving AIS signal?

Most the traffic I see is outside the Bradfield bridge.
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Old 21-01-2012, 18:01   #14
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Re: Receiving AIS signal?

Quote:
Originally Posted by delmarrey View Post
Most the traffic I see is outside the Bradfield bridge.
Just switch to the AIS channels and listen if some noise is breaking ur squelch. Might take some looooong minutes. Swich on ur AIS and look whats coming in. decodible signals? Did u set the right speed 38.400bd ? Can u listen to the ports traffic on VHF? Then everything should work. It took me several month to get my system to work fine - and i stay here in a excellent location.
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Old 21-01-2012, 18:20   #15
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Originally Posted by christian.kautz
Just switch to the AIS channels and listen if some noise is breaking ur squelch. Might take some looooong minutes. Swich on ur AIS and look whats coming in. decodible signals? Did u set the right speed 38.400bd ? Can u listen to the ports traffic on VHF? Then everything should work. It took me several month to get my system to work fine - and i stay here in a excellent location.
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Takes some time to load ;-)
Regards, Chris
At this stage all I hear is static.. I'll see how it goes once I have the new antenna. I haven't been able to even hear the ports traffic at this stage but I'm still experimenting.
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