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Author Topic: Tarheel II Sudden High SWR All Bands  (Read 1660 times)
AE7VA
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Posts: 82




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« on: April 16, 2017, 01:59:47 PM »

I've sent this to Tarheel tech support, but while I'm waiting for a reply, I was wondering if anyone on this forum had an ideas.

I've been using the little Tarheel II successfully for over the last three years in the bed of my Ford F-150, mounted very similar to the pictures on the Tarheel website.

The SWR has now started reading infinite across all frequencies and I can't figure out why.  I was wondering if you had any ideas on what to check. Here's what I checked so far:

1. Coax. Checked still installed in the vehicle. Attached the SWR analyzer to the radio end of the coax and a dummy load to the antenna end and got a perfect 1:1 across all frequencies. So that appears okay.
2. I've replaced the SO-239 connector at the antenna and insulators to see what would happen and no change.
3. I've removed the ground strap and cleaned all the surfaces and reinstalled.  Resistance at highest was 1/2 ohm at all connections at various points along the path.  I could not find any ground problem to the bed of the truck (steel bed).
4. Just to be safe, I replaced the ground strap with a new one. Same 1/2 ohm readings.
5. I gently cleaned the coil per the instructions and the whole unit moves easily and freely up and down. It was actually very clean to start with, not sticky, no black streaks, still shiny etc.
6. Ensured that the connection end of the whip is clean and that the hole it seats in is also very clean. Set screw is tight.
7. The core on the control wire is wound as close to the antenna as possible per the instructions. I even went and added two more cores for safe measure.

I tune the antenna with a handheld MFJ SWR analyzer with its own independent power supply (internal battery) and I've used this configuration successfully with this Tarheel since I bought the antenna.

I'm at a bit of a loss now as to where the failure point is.  Could it be something within the antenna itself?

Thanks.

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WV4L
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Posts: 225


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« Reply #1 on: April 16, 2017, 03:53:49 PM »

Did you check that the plastic insulator on the top part of the mount is okay and the mast of the antenna is not making contact with the mount? Also check that the tab on the mast is seating properly in the insulator and that it is also not making contact with the mount.
Didn't see that on your list.
73

Wayne C.
WV4L
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AE7VA
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Posts: 82




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« Reply #2 on: April 16, 2017, 04:08:19 PM »

YEP I did forget to put that on the list. Yes, I did check that insulator; even replaced with a new one.  Had no change on SWR.
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WV4L
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« Reply #3 on: April 16, 2017, 04:13:48 PM »

YEP I did forget to put that on the list. Yes, I did check that insulator; even replaced with a new one.  Had no change on SWR.

Okay, I guess you should wait and see what Tarheel says. Let us know what the issue turns out to be.

73

Wayne C.
WV4L
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AE7VA
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Posts: 82




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« Reply #4 on: April 18, 2017, 06:03:40 AM »

You nailed it Wayne about checking for a short between the antenna and mount.

I found the problem after spending some more time checking it over after work last night.  In all my checks, I never checked to see if the antenna base was shorted to the mount with an ohm meter. I only did a visual inspection between the antenna base and the mount where there is a clear separation with a thick nylon washer.

When I put the meter from antenna base to mount, I got a reading of 170 ohms, clearly the antenna base was shorted to the grounded mount. The SO-239 stud (center conductor) was ever so slightly touching the mount.

Initially the SO-239 stud was a little loose, so I tightened it.  I thought it just vibrated loose from vehicle motion; and it may have. I didn't realize initially, but now remember, that in this mount there was a wafer thin insulating disk between the SO-239 stud and the underside of the mount that prevented the very lower part of the stud base (center conductor) from touching the mount. I only replaced the insulator between the top side of the mount and the base of the antenna, but never checked it with the ohm meter.  The lower insulating wafer must have disintegrated and disappeared over time (our Arizona heat can cause parts like these to dry out and crumble).  I used the same type nylon washer that I did for the upper part and inserted it on the underside of the mount.  A check of the base of the antenna to the mount now gives me an infinite reading; no more short circuit and she tuned to a nice 1.2 to 1.5:1.

I was so focused on the grounding strap and other grounds that I forgot that one simple check with the ohm meter.  Everything works perfectly again.
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WV4L
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« Reply #5 on: April 19, 2017, 06:03:28 AM »

Glad you were able to find the problem. Wink I once saw a similar problem where the stud was tightened to the point that the nylon washer was mashed Shocked and then tore and made contact with the mount.
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