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post #33 of Old 10-25-2013
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Re: VHF AIS radios

Well darn. I seem to have stirred the pot.

Originally Posted by Classic30 View Post
Originally Posted by SVAuspicious View Post
The place for an AIS receiver to be integrated is in a chartplotter. Many units, especially smaller ones, have already integrated GPS receivers. An AIS receiver would be an easy addition and avoid all the problems of integration with a fixed VHF. If you find one on the market next year remember you heard it here first.
Wouldn't that mean a PL-259 antenna connection on the chartplotter? To (most likely) an external splitter?? Coupled with the RF issues somehow I don't think any chartplotter manufacturer will be going down that path soon.
Good question. No. There shouldn't be a splitter. A PL-259 (or better a BNC) to an independent antenna would be better.

Originally Posted by Classic30 View Post
Perhaps we can agree to disagree, but to my mind, the only sensible place for an AIS receiver to be integrated is within the radio - VHF+DSC/GPS/AIS together with a single data stream to a non-GPS chartplotter or VHF+DSC/AIS with a data stream to/from a GPS-enabled chartplotter.
Lots of people disagree with me. *grin*

GPS chipsets are so inexpensive to the manufacturer these days that it is easy to build them into anything. Add a GPS to a VHF and DSC just works. Add a GPS and a small VHF receiver to a chartplotter and AIS just works. Admittedly we get back to the issue of whether a splitter is fundamentally bad as I maintain or not, but it becomes so easy to put a 19" antenna directly on the plotter that the issue becomes moot.

Originally Posted by Missingyou View Post
All this talk of splitters and antenna makes me think I should drop my mast this winter. I have a factory installed splitter feeding my AIS-B and VHF. I really want to install TV, Sirius/XM, and maybe an external WIFI(ideally it needs a pair) antenna. It could get busy up there and that would be a lot of work for a rigger.
So you have two transmitters and two receivers now and would like to add three more receivers and a transmitter. Do you have radar?

Without seeing your boat I'd say masthead VHF, spreader mounted AIS/VHF on one side and WiFi on the other (talk to Bob Stewart at IslandTimePC). TV can be stacked above the radar (presumably above your steaming light). Sirius/XM can be mounted on the pushpit or in a dorade box.

Originally Posted by Maine Sail View Post
I personally don't have much of an issue with the VHF / AIS factory made radios and don't tend to see any measurable performance differences between standard fixed mount and VHF/AIS combos. I do test them on every install with an SWR....
Hi RC - Sorry I missed you in Annapolis. I fell working on a customer boat and was a little busted up.

SWR testing is good but only shows an impedance match. It doesn't show the effectiveness of radiation. You can get a pretty good match into a light bulb (literally) but that doesn't mean the signal is getting out. There are objective means of measuring that but realistically talking to someone outside of the near field (see
) is a good measure. Talking to a number of stations is better yet. The SeaTow automated radio check system is one of the best things to happen for installers. I'm sure you do radio checks (off 16 *grin*) after testing SWR, right? You are one of the icons of doing the right thing so I'm sure you do.

Originally Posted by Maine Sail View Post
The problems I see most with VHF performance.....

Main VHF unit wired with too small of a power wire (18GA etc)

Piss poor Shakespere "pinch through the jacket" PL-259's (personally I think there should be a class action against these absolute POS connectors.)

Piss poor DIY and pro soldering of PL-259's (the #1 failure)

Lack of any SWR testing once installed and newly wired. Simply putting out a radio check really does very little to tell you what your actual performance may be over a long distance in an emergency.
I agree with all your points.

I only use silver-Teflon PL-259s and solder with a high wattage iron.

You have to measure SWR. You also have to do far field radio checks. One is really not enough.

Originally Posted by Maine Sail View Post
I would argue that worrying about a potential performance difference between an AIS/VHF and a standard VHF, in the real world of installed VHF systems on boats, is the least of our worries when it comes to VHF radios.....
I'm happy to talk to you about this. I don't have access to a service monitor any more. If you do we can prove this to ourselves one way or the other. If you don't I'll start looking for one down here and we'll set up a Skype so you can watch testing.

sail fast and eat well, dave S/V Auspicious

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