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Author Topic: Rig Expert AA-30 Analyzer question  (Read 803 times)
KD0ZGW
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Posts: 739




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« on: November 26, 2017, 06:35:04 AM »

Recording SWR plots for G5RV at 70' in shallow inverted V orientation.

Test SWR plots on dummy load are a nice clean line and G5RV scans are a "hashy" line.  Repeated scans give results varying by as much as 0.5 SWR.  Sometimes it's partly a flat line and part hash.

I cycled the switches in the tuner and remote ant. switch with no change in results.

Analyzer checks out fine into dummy load and 40M beam which shares feedline with G5RV from remote ant switch on tower to shack.

Wondering why the difference (clean vs. "hashy" line) and what it means for antenna performance.  Indicative of a problem?

G5RV antenna seems to work fine even with SS amp (which is fussy about SWR.)

Thx to anyone offering advice.

KD0ZGW
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WB6BYU
Member

Posts: 17194




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« Reply #1 on: November 26, 2017, 06:59:15 AM »

When I see a really noisy trace I assume an intermittent connection somewhere.
If it is only a small amount it could be the antenna blowing in the wind, or my
body moving relative to the feedline, or something else that varies over the time
it takes to make a measurement.

When there is common mode current on the feedline then the reading can
change depending on how firmly I'm holding / touching the connector shell.

But basically I assume it is an error in measurement methodology that I need
to resolve in order to get an accurate measurement.
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VK6HP
Member

Posts: 186




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« Reply #2 on: November 26, 2017, 07:34:08 AM »

Is the trace essentially repeatable from scan to scan, with the scan width set to one ham band? If not, I'd definitely suspect a poor connection.  RFI is another possibility but probably unlikely given your good measurement of the other antenna.

You might also check whether the open wire or ladder line stub is blowing around a lot, and maybe approaching metal structures.  The variations in my doublet SWR are not as large as you describe but I can see very small changes due to wind and rain acting on the antenna and the stub.
« Last Edit: November 26, 2017, 07:36:32 AM by VK6HP » Logged
KD0ZGW
Member

Posts: 739




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« Reply #3 on: November 26, 2017, 08:06:58 AM »

Hash could be from ladder line feedline stub blowing/twisting in the wind.  Ladder line is 2' away from tower at closest point. 

I'll check it again on a windless day.

40M beam on same tower does not show hash on SWR plots.

KD0ZGW
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WA3SKN
Member

Posts: 6526




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« Reply #4 on: November 26, 2017, 03:10:49 PM »

Have you checked any of these connections with an Ohmmeter?
Looks like a bad connection.

-Mike.
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KB1GMX
Member

Posts: 1505




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« Reply #5 on: November 26, 2017, 04:10:40 PM »

Have you considered RF interference?   BCB or other strong local
signals can cause similar effects.


Allison
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N3DT
Member

Posts: 1273




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« Reply #6 on: November 27, 2017, 10:54:45 AM »

I bet it's a loose connection at the g5rv. I had one on one of my loops and it acted like the trace was cutting in and out on my RE, but would transmit fine. I never did find where the bad connection was, I just cleaned up all of them and it went away.
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