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wildad
(@wildad)
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Joined: 2 years ago
Posts: 7
November 5, 2020 1:16 pm  

I have a Little Tarheel II mounted in my truck that is showing very high SWR (not infinite but several hundred). I have gone around a bit with the manufacturer and can't see what the problem is. I'm wondering if there is a mobile antenna guru in the club who could drop by for a look. 


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Mike - AD0WB
(@mike)
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Joined: 2 years ago
Posts: 12
November 5, 2020 7:36 pm  

Well, I'm no guru... But how about a few questions...

Has it ever worked - in other words, is this a new problem?

Are we testing with an analyzer?

How is it mounted - is the ground plane sufficient?

Does it ~ever~ come into resonance?

Have you tried a different antenna with the existing feedline?

Have you tried swapping the feedline temporarily?

Does the antenna move when commanded? (Had a friend who's ATAS was stuck)

I would think it would be resonant ~somewhere~. If so, does the sweet spot change when commanded?

Those might be a decent start.

73, and keep the squelch loose.

Mike - AD0WB


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wildad
(@wildad)
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Joined: 2 years ago
Posts: 7
November 5, 2020 7:47 pm  

Has it ever worked - in other words, is this a new problem? I'm not sure it has. I just haven't been able to use it much.

Are we testing with an analyzer? Yes. A mini1300 that works fine on other antennas.

How is it mounted - is the ground plane sufficient? Mounted currently on front fender, previously on aluminum tool box in back. Fiberglass bed though. No difference. Mounting seems to be similar to others in many pictures.

Does it ~ever~ come into resonance? SWR is very high and reception is horrible.

Have you tried a different antenna with the existing feedline? No.

Have you tried swapping the feedline temporarily? Yes-no difference

Does the antenna move when commanded? (Had a friend who's ATAS was stuck) Yes and the manufacturer says that means the antenna is fine.

I would think it would be resonant ~somewhere~. If so, does the sweet spot change when commanded? Just no reception.


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Mike - AD0WB
(@mike)
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Joined: 2 years ago
Posts: 12
November 5, 2020 9:19 pm  

OK, so we know the motor works... 🙂

Is the antenna new?

I'd throw an ohm meter between the coax center connector and the radiating element. Attempting to verify no open within the antenna. I believe there's a 'wiper' in there which slides along a coil. Plenty of opportunity for a faulty connection. While you're there, verify continuity from the antenna housing (while mounted) to the negative battery terminal - that should verify that the ground plane of the antenna is connected to the vehicle body.

You might throw a dummy load on the end of the coax and measure - for grins - just to eliminate everything from the antenna connector back.

As for resonance, I don't know your analyzer, but it'd be good to know if the antenna is resonant anywhere within the HF bands.

My thoughts: If there is continuity through from the radio to the radiating element, it should be resonant somewhere. That should be readable via an analyzer. Then if the antenna moves, that resonance should change. If it doesn't, that'd lead me to think there's an open circuit.

You might also do a full sweep with the antenna collapsed, and additional sweeps at various points along its travel. If there's an intermittent connection, that could help identify it.

Interesting.


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wildad
(@wildad)
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Joined: 2 years ago
Posts: 7
November 5, 2020 9:29 pm  

@mike Thanks. Will work on it tomorrow.


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