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Old 09-11-2013, 13:51   #1
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Swr reading on ais

Just installed a new ais transceiver. The manual is pretty week. Here is a screen shot can anyone explain the swr reading is this acceptable? The antennae is a Shakespeare that is suggested for use with ais. Think the coax connector may need to be redone. I am getting targets and system checks out okay.
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Old 09-11-2013, 16:05   #2
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Re: Swr reading on ais

This SWR reading of 2.3:1 isn't very good. Usually though, a bad connector will show a much higher SWR than this, unless the connector is at the far end of a long run of coax cable.

It may be that the antenna is tuned for VHF #16, in which case you might see the 2+ SWR at the AIS frequencies (which are at the high end of the VHF band).

So, it could be better, but it could be much worse, and this could be caused by several different problems. Do you have access to a VHF transceiver and a regular SWR meter? You could then check the antenna and cable at different frequencies. But otherwise if you think your connector is bad you might as well replace/redo it and see what you get.
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Old 09-11-2013, 19:33   #3
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Re: Swr reading on ais

A VSWR of 2.3:1 indicates that 16% of forward power is being reflected back from the antenna to the transmitter. Not all that bad, but even that power is not totally lost. A large part of that reflected power bounces back from the transmitter final to the antenna again, where 84% will be radiated.

Some of that reflected power does get dissipated in the final amplifier of the transmitter, and that can be bad for higher power transmitters. It is typically less of a problem for a low power transmitter, and probably not an issue for your AIS transceiver.

If you can get the VSWR lower by adjusting the antenna whip length up or down, by all means do it. If you can't, I would not sweat it too much. The effect on AIS performance will be negligible. Paul is right in that a problem in the connector doesn't often cause such a subtle spike in VSWR at these frequencies.
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Old 09-11-2013, 22:11   #4
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Re: Swr reading on ais

Quote:
Originally Posted by sabray View Post
Just installed a new ais transceiver. The manual is pretty week. Here is a screen shot can anyone explain the swr reading is this acceptable? The antennae is a Shakespeare that is suggested for use with ais. Think the coax connector may need to be redone. I am getting targets and system checks out okay.
I had the same problem when I installed my XB-8000. It turned out to be just one of the fine wires in the coax fitting sneaked in and was making contact to ground. Use an ohm meter to check your fittings. I did the first time but when I screwed on the fitting the fine wire slipped in to ground. They need to make better field fittings it took three try's to get the damn things right.

When coax was right my reading dropped to 1.1.

BTW, if the light continues to blink shut it down. Continuous use will damage the unit. It needs to have a steady green light.
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Old 10-11-2013, 09:50   #5
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Thanks all. It seems to work fine but I guess I will give a go and redo the coax terminal.
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Old 10-11-2013, 10:43   #6
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Re: Swr reading on ais

I had trouble when I installed a raymarine AIS (650) on the Pearson 424, the VSWR was too high. The software triggered a VSWR high fault over 2.1. Speaking to raymarine I learned they suggested 1.5 or better. I re soldered my connector and it dropped to 1.2 and works great.
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Old 10-11-2013, 12:09   #7
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Re: Swr reading on ais

My new powerboat (I still have VALIS, my sailboat!) had a factory-installed Garmin AIS receiver, that included a splitter to share the antenna with the VHF transceiver. The AIS was receiving OK, but not great. The VHF worked in a radio-check with a close-by vessel, but it was weak beyond a few miles.

I brought my SWR meter down to the boat and started testing. The SWR into the antenna cable was 5:1 or worse -- it was huge.

I was hoping it was a connector problem, so I measured with an Ohmmeter: virtual dead short. Since the antenna is normally a dead short, this might be OK (an open circuit would be bad). The antenna had no connector, just the cable coming out the bottom, so I had to hope the problem was a shorted connector. I cut off the connector and measured it with an Ohmmeter which verified the short, cleaned it out, and re-soldered it.

What surprised me was how well the AIS and radio worked even with the shorted connector. I guess it was just a whisker of shield that was shorting. It worked well enough to not be obviously broken, but now it works *much* better. The SWR is under 1.5:1 now.
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Old 11-11-2013, 14:10   #8
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Re: Swr reading on ais

There are really often issues with AIS splitters. They do reduce Antenna effectiveness for BOTH the VHF and the AIS. There are one or two around that are powered, and claim zero loss, but we recommend a separate antenna...

Just my 2c worth!!

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