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ContinuousWave: Small Boat Electrical
ICOM VHF-AIS Combination Radio
|Author||Topic: ICOM VHF-AIS Combination Radio|
posted 03-20-2008 01:35 PM ET (US)
[In reference to an ICOM radio announced for sale in France and the UK for approximately $1,100 which contains a VHF Marine Band radio and an AIS receiver]
Got to love the Europeans. Cutting edge great idea. Hope it makes its way across the pond.
posted 03-20-2008 03:02 PM ET (US)
Icom is Japanese.
posted 03-20-2008 03:09 PM ET (US)
No Chuck it's Swedish by way of Japan and heaven forbid it's not a SH so it must be inferior.
posted 03-20-2008 03:57 PM ET (US)
Combining an AIS receiver into a VHF Marine Band radio is a good idea. You already have about 90-percent of the components needed. An AIS receiver just needs to monitor a couple of channels, demodulate the frequency shift keying into data, and output the data on a serial port.
Right now you can buy a dedicated AIS receiver for about $250. In contrast, you can buy a complete DSC Class-D radio for about half that price. If you combined the two, you ought to be able to make a Class-D DSC radio with AIS receiver for $150, or about $25 more than the current radio-only price.
|Casco Bay Outrage||
posted 03-20-2008 05:31 PM ET (US)
At ~575 BP that is really expensive. This translates into $1100 USD.
Not sure how you get from $1200 to $150, even if you subtract VAT
posted 03-20-2008 08:52 PM ET (US)
Before a combination VHF Radio and AIS Receiver becomes attractive, it will have to cost LESS than buying separate units. Right now you can get a nice Class-D DSC VHF Radio for about $125. And you can get a minimalist AIS receiver for $189.
Check out the Milltech Marine AIS receivers:
posted 03-21-2008 05:33 AM ET (US)
Bluewaterpirate: Would you explain that "Swedish by way of
From http://www.icomamerica.com/en/profile/default.aspx ":
Sure sounds Japanese to me.
posted 03-21-2008 07:59 AM ET (US)
I was pulling your leg but I guess the spoof passed you by. It's apparent that ICOM is Japanese but thanks for pointing it out. What I should said ICOM UK/France were releasing new VHF models with AIS functionality.
The real value is two fold one is the new units will use a common VHF antenna (negates the requirement for a second VHF antenna in the standalone AIS install). Second it will save space (i.e. having to find space below decks to mount the standalone AIS receiver).
The NMEA wiring should be the same as the current units. The market will drive the price for sure.
posted 03-21-2008 08:32 AM ET (US)
Using a common antenna is a big plus for a unit that combines a VHF Marine Radio with an AIS receiver. On small boats there is not room for two antennas. Also, the presence of a second antenna may distort the pattern of the first antenna, and that may not be desirable.
A combined VHF Marine Radio with Class-D DSC rating and AIS receiver will actually have THREE receivers operating all the time:
--tunable receiver for VHF Marine Band general use
posted 03-21-2008 11:53 AM ET (US)
IIRC there are two AIS channels, so a good AIS/VHF combo unit
would have two dedicated AIS receivers for a total of four.
posted 03-21-2008 12:37 PM ET (US)
There are two AIS channels, but there is no requirement that you have to monitor both of them--a receive-only AIS device is not a recognized AIS configuration. It's more of a hobbyist device for the technologically avid boater.
At the moment in the US, only Class-A AIS units are available for sale due to the FCC dragging its feet on making a decision on Class-B units. The Class-B units would be more applicable to recreational vessels, or any vessel not required by law to carry a Class-A AIS transponder. When Class-B AIS becomes available in the US, you will probably see an increase in interest among recreational boaters in AIS installation.
Part of the hold up with Class-B AIS implementation seems to be the potential interference that AIS operation might cause to adjacent channels in the VHF Marine Band. That spectrum was "sold" to marine radiotelephone shore station providers. Even though the usefulness of marine radiotelephone shore station facilities has just about been reduced to ZERO by the ubiquity of cellular telephones (whose range is about the same as VHF Marine radios, more or less), the operators of those shore stations are asking for consideration from the FCC for the value lost in their channels which might occur if Class-B AIS is permitted. While the rest of maritime community goes forward with Class-B AIS, the United States is being held hostage by a few private companies who want to protect their financial interests.
posted 03-21-2008 07:50 PM ET (US)
But, since there are two AIS channels, what I said, "a good
AIS/VHF combo unit would have two dedicated AIS receivers for
a total of four." still applies. FCC isn't relevant. Class
B isn't relevant. GOOD is relevant.
posted 03-22-2008 04:57 PM ET (US)
Chuck--You have applied an arbitrary judgement that in order to be considered a "good" AIS receiver it has to have the capability to receive both channels simultaneously.
The low-cost AIS receivers do monitor both of the AIS channels, but they just do not monitor them both simultaneously. The low-cost receivers apparently scan both channels and obtain information from both. There is no official classification of receive-only AIS devices, so it is hard to determine that only those devices which possess the ability to receive simultaneously are to be considered as "good."
Vessels which are underway transmit their AIS broadcasts at intervals of two to ten seconds. Given this frequent repetition of the broadcasts, it seems reasonable to me, without making a careful mathematical analysis, that monitoring of one AIS channel at a time ought to give reasonable results. Considering that the movement of most commercial vessels is generally at speeds below 10-MPH, an interval of 10-seconds implies a change in position of about 146-feet. I don't think that AIS reception as a hobbyist is going to suffer if a vessel position update is ten seconds old. The vessel will only be 146-feet out of position.
I would like Chuck to demonstrate a scenario in which a receiver which is not able to monitor both AIS channels simultaneously would suffer a significant degradation in performance compared to a device which is capable of monitoring both channels simultaneously. If Chuck demonstrates such a scenario, then I will be more inclined to agree that only AIS receivers which can simultaneously monitor both channels ought to be considered as "good."
posted 03-23-2008 10:57 AM ET (US)
Here is an interesting discussion from panbo.com on the topic of AIS reception using a single-channel-at-a-time receiver compared to using a simultaneous dual-channel receiver: http://tinyurl.com/yqpsgf
The most worrisome degradation is likely to occur in the case of a fast-moving Class-B vessel. Such a vessel might move a significant distance between received position reports. However, AIS is not really intended as a collision avoidance system. And since at the moment there are no Class-B transponders for sale or in use in the United States, it makes it something of an academic argument. In the event that Class-B transponders become approved for sale in the United States, and there is very widespread adoption of them among non-madatory carriage vessels, then perhaps a strong argument could be made that a "good" AIS receiver must be a simultaneous dual-channel receiver. However, I think at that point in time there will be many more products to choose, and it might very well be that a Class-B transponder may come down in cost to the point where it is as affordable as the current receive-only products.
posted 03-23-2008 09:35 PM ET (US)
Jim, you've been a vocal supporter of Class D DSC units, which
have a separate receiver for Ch. 70, as opposed to DSC units with
a single receiver that scan Ch. 70, along whatever voice
channels the user has programmed. The need for two receivers
for AIS is an extension of your "Class D is good" logic.
In fact, it's more important for AIS because in a busy area
there's traffic several times a second on the AIS channels.
There's DSC traffic maybe every minute or so.
One more interesting point: At four receivers, it's probably
I'll predict that for 2009 most of the high end VHF units will
posted 03-23-2008 10:32 PM ET (US)
I compiled a quick list of AIS receivers currently available:
The dual receiver units range in price from $700 down to around $440. There is one unit, the EasyAIS, which appears to be a dual channel unit and is selling in the U.K. for about $325 (in the equivalent amount of Pounds Sterling). I am trying to get more information about it.
With a dual receiver unit, there are two streams of data being received. That data has to be buffered and then combined into a single serial output. This adds some additional complexity to a parallel receiver.
If you analyze a VHF Marine Radio with Class-D rated DSC features, it seems like it would have all the elements of an AIS transponder:
--dual parallel receivers
If Standard-Horizon can make a very nice VHF Marine Radio with DSC Class-D rating and sell it for less than $150 (the GX-1500-S), then an AIS Class-B transponder ought to be able to be made for about the same price, once the volume ramps up. (By the way, while web browsing this weekend I noticed that a major U.K. supplier of marine electronics listed the Standard-Horizon Class-D GX-1500-S as the "top selling" VHF Marine Radio.)
As for software-based radio designs, that probably is the future. I don't know how far in the future, though. I have seen several trade magazine articles on digital radios in which the entire radio is basically a really high-frequency digital signal processor and everything is implemented in software.
posted 03-24-2008 08:15 AM ET (US)
Re encouragement to get Class-D rated DSC VHF Marine Radios:
I'm in good company; the United States Coast Guard also recommends a Class-D radio as the choice for a marine VHF Radio. In the case of a DSC radio, we're talking about an important life saving device. The more boats equipped with DSC radios that are continuously monitoring the DSC channel for a distress message, the more likely the message will be received.
In the case of a receive-only AIS, at the moment they're just a high-tech gadget for most purchasers. Now I will agree that if I did most of my boating at night in an area of really high traffic commercial shipping, say the English Channel, then I would consider an AIS receiver as something more than a gadget.
Will use of AIS receivers by non-mandatory carriage vessels become as widespread as VHF Marine radios? Probably not.
posted 04-02-2008 11:49 PM ET (US)
Another [consideration] is the antenna. During the great rush to outfit commercial vessels with AIS, many found that certain units were sensitive to high VSWR created by using an antenna cut for 156 MHz instead of 162MHz.
You would have to inhibit the AIS during voice comms and DSC calls.
posted 04-03-2008 08:22 AM ET (US)
The VSWR of the antenna on the AIS frequencies should not be of great concern in the case of an AIS receiver. While it is true that the situations of transmitting or receiving on an antenna are somewhat analogous, in the case of receiving there is not a great deal of concern with the VSWR on the transmission line between the antenna and the receiver. There is excess gain available in the receiver which overcomes any small loss caused by the VSWR being slighter higher.
Concern about the VSWR of the antenna may be proper in the case of a Class-A transponder installation, where the AIS transmitter may not be happy if it has to transmit into an antenna with a high VSWR.
Sharing a common antenna for simultaneous transmission and reception on closely spaced frequencies is very difficult, and my assumption is that any combination device would not be able to receive while it was transmitting.
On the other hand, on a small boat there is not a lot of room for installation of separate antennas, and even if two antennas were used, they probably would not be located very far apart. This means that it is likely that during transmission on one antenna, reception on the other antenna would be degraded somewhat.
I believe that in the DSC specification for Class-D radios there is no requirement for the DSC channel to maintain reception while the radio is transmitting on the normal voice channels. It is likely that an AIS receiver sharing that same antenna would also have to be disconnected from the antenna during transmission.
posted 04-03-2008 10:17 PM ET (US)
Roloaddict's mention of the VSWR on an antenna used for both VHF Marine Band and AIS sent me checking on the frequencies involved. His concern is well founded.
AIS 1 = 161.975
VHF Marine Band Frequencies
Channel 01 = 156.050
The entire VHF Marine band is only 1.375 MHz wide. The AIS channels are 4.55 MHz above Channel 88. So that means the gap between VHF Marine and AIS is about three time greater than the width of the whole VHF Marine band.
I see now why some antenna manufacturers are offering special AIS versions of some their antennas. The antennas are probably retuned for 162-MHz operation. This is more important for transponders, however, than for receive-only devices.
posted 04-04-2008 07:36 AM ET (US)
Jim ,let me share my experience with AIS. Late last summer I was involved with teaching a marine photography course in Newport RI. This is a fairly active shipping area. I knew I would be busy with photography, boat handling, people on my boat and watching out for the ship/barge traffic on Narragansett Bay. So I thought this would be a fine time to add a AIS reciever to the Garmin display. Not having lots of time to rig a antenna I just used a short rubber antenna from a scanner. The AIS receiver was mounted in the center console of my Nantucket. The range of ships that were shown were about 6 miles which was pretty good for my purposes. It gave me a situational awareness of what was going on around regarding the big stuff. I am sure if I had a proper antenna up at console height things would have been lots better but I was quite please with what I was seeing. The receiver was the Millitec 100. The cost of the setup was minimal and it was fun to watch to see who was putting out the correct info as well.
posted 04-04-2008 08:34 AM ET (US)
Thanks for the first hand report on AIS reception. On most large ships you can estimate that their AIS transponder antenna will be about 35-feet above the water. This gives them a radio horizon of approximately eight miles. On a small boat with an antenna only three feet above the water, the radio horizon will be about two miles. Combining these implies that even with a poorly located antenna on a small boat you should have about a ten mile range. Your observation of a reliable six mile range is quite reasonable.
I am glad to hear that the Milltech Marine AIS receiver worked well for you. Their current model is the SR161. The retail price is $189. It sounds like a lot of fun for a modest investment.
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