AIS Antenna Not Working

[natew]

Trying to get a new ais transceiver and antenna working. I'm down to nothing more than the factory supplied cable for the antenna and a push on style connector. When I connect the antenna the ais transponder reports a SWVR of between 60 to 1 and 100 to 1. I've remade the connector four times already and removed all interference. Is my antenna maybe faulty or something else?

The antenna is a Shakespeare galaxy ais antenna and the AIS is the emtrak B100. Appreciate any ideas and input. Thanks


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[CptLawrence]

have you tried a different antenna? any vhf antenna will work, did you check an ais website for nearby transmissions?

[MarkJ]

Yeah, can you connect the AIS to the vhf antenna to check it?

Did you solder the central part of the connector? And did you ensure not one thread of the outer cover pushes down to short the center when you made the connector?

Did you swear at it?

[natew]

Trying to figure out if I have the right connectors and cables to put the ais on the vhf antenna but they are a a fair distance apart. I tried solder and push on connectors with same results.


I swore at it a few times and burnt myself once... Neither helped.


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[natew]

Works beautifully on the vhf antenna.


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[witzgall]

Mpst likely you made an error when connecting the connector. Even one stand touching can cause the problem you are describing.

Chris

[MarkJ]

Good. Now you know its not the ais.

[socaldmax]

Assuming that you did make up the PL259 connector properly, there's a chance that the antenna itself is not making good contact with the mount. I took a look, it appears the antenna uses an NMO mount. Many NMO mount antennas (Larsen, for one) use a flat spring contactor for the center conductor that is easily smashed down and then makes poor contact, resulting in the crazy SWR numbers you saw. Take a minute to unscrew the antenna, pry the flat spring up a little bit, screw it back on and see if that helps.

Another possibility is it's mounted on something too thick, preventing the antenna from screwing down all of the way and making a good connection.

[El Rubio]

Chances are, you shorted one of the connectors as you installed them. I'm assuming you don't install these pl259's very often. Standard PL259's are difficult to properly solder, so for this reason, I always recommend a relatively cheap coax crimping tool and crimp-on connectors. A decent crimper can be had for around $30 and connectors are about the same price as standard solder on. Most Crimp on Pl259's allow you to solder the center pin.

VSWR measurements like you have indicate either a short or open. I would guess a short and you can measure that if you have a multimeter. Remove the antenna whip and from the radio end of the cable measure continuity or resistance from the center pin to the connector housing.

If you are confident the feedline is good, inspect the antenna base and mount as describes by others here.

Good luck with the repair.


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[mtyler]

OK, radio good on another antenna!
Put a meter on the antenna cable (disconnected at BOTH ends). Is the center connector shorted to the shield? What is the continuity of the shield (end to end) and the same for the center conductor.
Test the antenna: Continuity from the connector center conductor to the antenna (should be low impedance - just a few ohms or less). Continuity from the shield to the center conductor (this should be HIGH).
Don't let your fingers provide any continuity when doing the tests.

[socaldmax]

That reminds me of another, easier test you can do.

1. Disconnect cable from the radio and check the resistance of the center to outer conductor.

2. If it reads shorted, or very low resistance, one or the other end of the cable is shorted, don't assume that they don't screw up cables from the factory.

3. If it reads open (which would be a normal reading) that, in conjunction with the extremely high SWR would make it appear that you have either an open at the antenna (flat spring not making contact) or in the cable.

[SoonerSailor]

You need to have the cable disconnected from the radio AND the antenna if you check for a short with an ohmeter. Some VHF antennas will be a short at DC but not at VHF frequencies - which can be normal.


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[socaldmax]

Originally Posted by SoonerSailor

You need to have the cable disconnected from the radio AND the antenna if you check for a short with an ohmeter. Some VHF antennas will be a short at DC but not at VHF frequencies - which can be normal.


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That's good to know. Which antennas exhibit that behavior? I have Laird, Larsen, MFJ, Antenex and Diamond VHF whip antennas here, and none of them indicate a short with a meter.

[nigel1]

I think Shakespeare's V-Tronix might be one, this is from their instructions for the VHF antenna:
Note:
To check continuity, there should be a
10k ohm resistance between the cable inner

Note: To check continuity, there should be a
10k ohm resistance between the cable inner
conductor and the outer sheath.

[socaldmax]

Originally Posted by nigel1

I think Shakespeare's V-Tronix might be one, this is from their instructions for the VHF antenna:
Note:
To check continuity, there should be a
10k ohm resistance between the cable inner

Note: To check continuity, there should be a
10k ohm resistance between the cable inner
conductor and the outer sheath.

That's good to know! Although I wouldn't call 10k ohms a short. That's a very specific impedance.

All of the antennas I listed above read open, even on the mega ohm scale. I tried a little experiment with my Antenna Analyzer (MFJ 259B) by opening/shorting the closest connector, removing the antenna from the mount, shorting the cable at the mount, but the SWR readings weren't meaningful enough to help out in this case. I was hoping to duplicate the symptoms, but the results were different enough I didn't think they would be helpful.