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Author Topic: Cushcraft MA5B. High SWR  (Read 1841 times)
KB3ELT
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Posts: 3




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« on: March 24, 2009, 04:18:17 PM »

Greetings everyone! I'm curious to see if anyone can possibly offer a little insight.

I have an MA5B, roof mounted and it's been a great little antenna in the month I've owned it. I had it tuned as follows:

1.2:1 at 14.300
1:1 at 21.200
1.3-1.6:1 on 10m
12m and 17m are very low across the band at approx. 1.2:1.

Just today I went to check the SWR with my analyzer and found 20 meter is now 3:1 or higher and 15 meter is that high as well. 10, 12 and 17 seem unaffected.

I went up on the roof and checked all the connections and remeasured the antenna's dimensions, of which all are the same as when I first installed it. I've taken off the matching network and tested continuity between all the connections and there doesn't seem to be a problem there.

Could a trap have gone bad? I only have the capability of running 100 watts so I'm thinking I shouldn't have melted anything as I've read in other posts.

Ideas?

Jeff
KB3ELT
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W8RPE
Member

Posts: 108




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« Reply #1 on: March 24, 2009, 04:58:07 PM »

Jeff,

Have you checked the traps for water buildup and made sure the drainage holes are open to allow water to drain from the traps?  If nothing has changed with you system then it's a matter of trouble shooting until you find the problem.  From what you've told us water in the 20/15 traps sounds like a possibility.

Ron
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K0UA
Member

Posts: 55




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« Reply #2 on: March 24, 2009, 06:18:56 PM »

sounds like water to  me also, but could be connection problem in the trap.. you can measure them with a good digital ohm meter, the guy at cush craft can tell you how. I did this when I had a problem and suspected the trap. turned out I was stupid and had reversed the trap.
But the measurments  showed what was expected according to the diagram he sent me. This is a stupid question... but you did orient the trap with the weep holes down didn't you?
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N6AJR
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Posts: 9892




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« Reply #3 on: March 24, 2009, 06:50:28 PM »

I had one go bad on me,  be sure the holes in the traps point down to let the water out, and mine had a plethoria of bugs inside the trapsd on one set of traps that shorted out the coils... replaced traps and worked fine,  you may need  to clean your traps???
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KB3ELT
Member

Posts: 3




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« Reply #4 on: March 24, 2009, 07:17:41 PM »

I have the traps oriented with the drain holes downward. I tried to get them as exactly down as possible. Also I have the them positioned with the arrows facing outwards.

Tomorrow morning I'll recover the traps and inspect them. I'm assuming the traps I should be looking at in particular are the MT-1's on the 15/20 driven element.

Hopefully I'll be coming back on here with a positive update.

Thanks to all for your help thus far!

--jeff
KB3ELT
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W6VPS
Member

Posts: 369




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« Reply #5 on: March 25, 2009, 12:03:09 AM »

Be sure to check the matching network as well. Could be something inside has been toasted. There is also a known problem with early MA5B's having some toasted traps as a result of using high power.
Let us know what you find and good luck.

Paul/W6VPS
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AD4U
Member

Posts: 2153




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« Reply #6 on: March 25, 2009, 07:35:02 AM »

If all the suggestions posed so far do not uncover the "problem", try using a bit of real RF from your rig and read the SWR on a good watt meter instead of the "antenna analyzer".

Dick  AD4U
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WA3SKN
Member

Posts: 5443




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« Reply #7 on: March 25, 2009, 08:27:43 AM »

Check the coax and connectors with a known good dummy load.
Then you can start looking at the antenna connections and possible water issues.
Something has changed.  Time to find it!
Good luck on the project!

-Mike.
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KB3ELT
Member

Posts: 3




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« Reply #8 on: March 25, 2009, 09:49:37 AM »

Problem solved.... sorta.

After disassembling and inspecting the MT-1 traps and reinstalling them I have found my SWR has returned to normal. There were no signs of moisture in the trap canister or any signs of arcing. I did however find a sliver of metal about the size of a splinter on one of the coils. I wished I found a definitive "AH HA!", but I'm happy to report an SWR of 1:1 at 14.300 again!

Thanks all for your help and 73!

--jeff
KB3ELT
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N5LRZ
Member

Posts: 0




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« Reply #9 on: March 25, 2009, 09:50:33 AM »

In addition to the above suggestions regarding moisture problems, which I agree with by the way, you might first give the antenna a good visual checking.  

SOMETIMES things fall off antennas or break off in high winds.

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K2DC
Member

Posts: 1346


WWW

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« Reply #10 on: March 25, 2009, 12:37:50 PM »

Jeff,

   If you found the sliver of metal on one of the 15M coils, you may have found your "AH HA".  A problem with the 15M trap would impact 15M and 20M, but not 10M.  12M and 17M are on a spearate rotatable dipole.

GL & 73,

Don, K2DC

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KA2UUP
Member

Posts: 388




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« Reply #11 on: March 25, 2009, 12:58:46 PM »

After 7 years, I have never had a problem, but I am aware of the interface box and traps having issues.

One thing I strongly would take a look at is at the twin leads attached to the matching box.  Corrosion of the nuts attaching the leads to the box, as well as a lose lug could be the culprit.

Another possibility causing high SWR is something shorting the active elements to the boom.

Good luck and let us know how you make out.  It will be good "lessons learned" for the community.

Bart @ KA2UUP
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