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Author Topic: SWR vs Tuner vs Amp  (Read 1437 times)
KJ6TSX
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Posts: 116




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« on: April 07, 2013, 05:35:58 PM »

I have run across a problem I don't quite understand?
turned on the radio this morning (Yaesu FT950) SWR perfect made a few contact everything great with amp on (Dentron 1000) turned amp to standby SWR goes High, turned amp off swr high. Turned antenna selector on antenna tuner to direct SWR drops to 1:1?? the signal is still going through the amp. and this only happens on 1 antenna the other antenna does not have any problems.
Any help would be appreciated
Thanks
George
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W5DXP
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« Reply #1 on: April 07, 2013, 05:58:33 PM »

Any help would be appreciated

I've had a similar-sounding problem with my IC-706 and had to do some grounding modifications. Your Yaesu may be picking up enough feedback in that one configuration to cause a parasitic oscillation.
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AD6KA
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Posts: 2238




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« Reply #2 on: April 07, 2013, 05:59:42 PM »

Have you tried running the amp into a dummy load
and testing for this phenomenon?

How "high" is your "High SWR"?
(Sound like you are mesuring this on the rig's SWR Meter, right?)
And your setup is rig->amp->external tuner->antenna, right?

Is this happening on all bands?

What antenna are you using that makes this problem appear?
Need some more info....
Quote

SWR perfect made a few contacts everything great with amp on (Dentron 1000)

turned amp to standby SWR goes High, turned amp off SWR high. Turned antenna selector on antenna tuner to direct SWR drops to 1:1?? the signal is still going through the amp.

This doesn't make any sense. At first glance it sounds
like an amp tuned input problem, but that would STILL
appear with the external tuner set to "Direct".

You are transmitting with amp on standby?
 Need some more info....
« Last Edit: April 07, 2013, 06:02:24 PM by AD6KA » Logged
W8JX
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Posts: 6456




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« Reply #3 on: April 07, 2013, 06:38:15 PM »

Any help would be appreciated

I've had a similar-sounding problem with my IC-706 and had to do some grounding modifications. Your Yaesu may be picking up enough feedback in that one configuration to cause a parasitic oscillation.

My nickle is on this or you are getting some RFI with tuner/antenna combo in line.
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KJ6TSX
Member

Posts: 116




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« Reply #4 on: April 07, 2013, 09:53:19 PM »

I'll try an answer the questions in order
Quote
How "high" is your "High SWR"?
(Sound like you are mesuring this on the rig's SWR Meter, right?)
And your setup is rig->amp->external tuner->antenna, right?

SWR on tuner about 1:2 SWR on Rig 1:3 and I get a High SWR displayed on the rig with reduced power output

Yes rig, amp, tuner (even went out and double checked)

Quote
Is this happening on all bands?

What antenna are you using that makes this problem appear?

This only happens on 10 meters the antenna a Moxon Vertical cut for 10 meters. the other antenna switched from the tuner is a parallel inverted V and works fine

Quote
You are transmitting with amp on standby?
Yes the relay only closes when amp is in transmit mode, also same problem when amp OFF

Quote
I've had a similar-sounding problem with my IC-706 and had to do some grounding modifications. Your Yaesu may be picking up enough feedback in that one configuration to cause a parasitic oscillation.

I currently have a 18gauge wire independently connected from the rig amp and tuner to to a grounding bar that connects to a grounding rod in the ground. the antenna is grounded to earth but not interconnected with the grounding in the shack except for the coax

Glad to see that it wasn't just me that thought this strange

Thanks for all the Help
George
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W5DXP
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« Reply #5 on: April 08, 2013, 11:36:07 AM »

Glad to see that it wasn't just me that thought this strange

When I said "grounding modifications", I meant inside my IC-706. Now I am wondering if your problem could be common-mode? Do you have any common-mode chokes installed?
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KJ6TSX
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Posts: 116




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« Reply #6 on: April 08, 2013, 08:34:12 PM »

Quote
Do you have any common-mode chokes installed?
I have is a choke balun made with some rg8 coiled on the antenna and I do have excess coax coiled hung on a nail just before it goes out of the shack. I also have ferrite beads on the coax about 1 foot from the ant tuner.
I know I am rambling about things that I would think have no bearing on the problem?? But I could be wrong<GRIN>
Thanks
George
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KB4QAA
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Posts: 2446




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« Reply #7 on: April 09, 2013, 12:24:11 AM »

Quote
...the ntenna is grounded to earth but not interconnected with the grounding in the shack except for the coax

Why would you ground a Moxon antenna?
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KJ6TSX
Member

Posts: 116




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« Reply #8 on: April 09, 2013, 10:20:30 PM »

Quote
Why would you ground a Moxon antenna?
I wouldn't think you would have to?? and I didn't think adding radials would help but it did.
I don't profess to know what I am doing Grin
Thanks
George

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