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ContinuousWave: Small Boat Electrical
AIS Receive Antenna for Shore Station
|Author||Topic: AIS Receive Antenna for Shore Station|
posted 01-15-2012 03:32 PM ET (US)
Please use this thread for discussion of my article (in the REFERENCE section) on AIS receive antennas for a shore station. See
posted 01-15-2012 06:17 PM ET (US)
Very interesting Jim, thanks.
It amazes me that even after more than 100 years, people are still developing new, innovative antenna designs.
posted 01-16-2012 06:50 PM ET (US)
Jim--I still think you should try it down on top of the work building in the spring. See what the range might be!--Don
posted 01-18-2012 09:12 AM ET (US)
The AIS antenna I describe in the article has a directional characteristic which makes it appropriate for installation in a location where the AIS targets will all be located in one particular quadrant of the compass. Locating the antenna in downtown Detroit, near the river, would require an antenna with a broader directional pattern, as the azimuth to the targets would have roughly a 180-degree span. An antenna with a pattern whose main lobe is only 90-degrees wide would not be the optimum choice.
My AIS Shore Station has not yet found a permanent home. One further technical refinement remains to be explored: using a network connection to convey data from the receiver at a remote location. I will be doing some experimenting with this aspect in the near future. Once the remote data connection is perfected, the number of possible receiver sites will increase.
posted 01-18-2012 04:01 PM ET (US)
I just heard on the radio that the Soo locks closed today, so there probably won't be too much traffic for you to monitor until spring.
posted 03-25-2012 11:07 AM ET (US)
Over the winter I changed the feedline connection to the AIS antenna, with the goal of shortening the length of the connections as much as possible. The new connection is shown in the illustrations in the article.
I suspected that this would affect the VSWR curve, but I could not measure it in the winter due to the cold weather. I retested the VSWR of the antenna this Spring with the arrival of warm weather. I found the VSWR had been affected by the change in the feedline connection. I had to lengthen the driven element loop to compensate. The new dimensions and a new VSWR curve are now shown in the article.
Next step is to reinstall the antenna on the roof. This should come soon.
posted 03-25-2012 08:38 PM ET (US)
I put the AIS antenna on the roof this afternoon, and it was soon receiving three ships, all in the Detroit River area. It is just amazing to me to connect this little software-based receiver to the antenna, then in a few minutes to collect all sorts of information from ships in the vicinity, and to see the details--even the outline of the ships--drawn accurately on a chart. I understand the technology completely, but it works just like magic.
Alas, putting the AIS on the same mast as my Channel-9 television antenna seemed to disrupt reception of CBET-TV Windsor, Ontario, Canada, which is my best source of a high-definition picture of the CBC's Hockey Night In Canada. The presence of the AIS antenna under the Channel-9 antenna caused the signal-to-noise ratio of my CBET signal to drop to 16-dB from 24-dB, putting the signal into the marginal territory. Well, we cannot have our hockey game picture freezing up on us, so I had to tear down the AIS receiver. We'll have to investigate further into the interaction between the two--and wait for the hockey playoffs to be over in June--before we can put the AIS antenna back up there.
posted 03-26-2012 11:44 AM ET (US)
So, for the rest of us, the receiver is using PFM technology.
posted 03-26-2012 12:43 PM ET (US)
Sounds like you need a tower. In for a penny, in for a pound.
posted 04-29-2012 07:17 PM ET (US)
Update on the G0KSC antenna I have for use as an AIS shore station:
As I mentioned above, in late March when I installed the three-element Yagi antenna on my roof-mounted mast there was interference with my television antenna, another custom antenna installation dedicated to receiving CBET Windsor 9, the local CBC outlet across the border in Canada. I suspected that there was a problem with the TV antenna. Today I finally had a chance to get back on the roof and make a few changes.
The Channel-9 TV antenna was exhibiting rather flaky performance, with extreme sensitivity to the coaxial transmission line orientation. This led me to believe that the antenna balun was not working properly. The balun transformer is used to convert the 300-ohm balanced feed point of the antenna to a 75-ohm unbalanced transmission line. Based on what I was observing with the extreme sensitivity to the transmission line placement, I suspected the balun was no good. I tore down the whole antenna mast installation--necessary to get to the top mounted Channel-9 Yagi--and replaced the balun. After re-erecting the mast with the Channel-9 Yagi back in place, the signal level on the TV receiver improved about 6-dB (or about four-times more signal), producing the best reception seen to date and a signal-to-noise ratio of 29-dB. Channel-9 from another country is now coming in with a signal as strong as some of the local stations a few miles away!
Encouraged with this result, I then installed the G0KSC antenna on the mast below the Channel-9 antenna. There was no evidence of interaction; the signal-to-noise ratio on the television receiver stayed at 29-dB.
For this installation of the AIS antenna, I have a new transmission line using RG-8214 coaxial cable. This is a consumer-grade foam dielectric 50-ohm 1/2-inch transmission line. Is not the finest possible coaxial cable, but it is sufficient for this application where the transmission line only needs to be about 40-feet long.
The G0KSC AIS antenna is now working beautifully. I even set a new DX (distance) record when I received an AIS broadcast from a vessel in Lake Erie at a range of 55-miles. The signal was not stable and soon disappeared, but it did pop in for a minute or two. The vessel was down in Lake Erie and just about on the center of the antenna's main lobe. I was impressed with the performance in consideration of the rather low mounting height. Copying a 12-watt data signal at that range is impressive for an antenna only 20-feet off the ground and shooting through an urban setting.
posted 04-29-2012 08:59 PM ET (US)
Still say try the top of your work bldg. How would some Belden 9914 or 9913 work? Thought I had a partial roll around here somewhere.
posted 04-29-2012 11:27 PM ET (US)
Don--Now that I have a steady source of AIS signals, I can work on the next phase of the project: a serial to ethernet TCP-IP server, so the receiver can be remotely located and stream its data to a remote host. Once I get that hardware purchased, connected, and configured, the AIS receiver will be ready to be located in an appropriate spot. The receiver and serial data server will only consume about 5-Watts of electricity, so it will not be a burden on the host site to power them. But I want to make sure I have a rock-solid configuration before I put the hardware someplace that I won't have easy access to visit for service.
That 9913 or 9914 is good coaxial cable. It has nice low loss at 150-MHz. It could be very useful.
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