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Author Topic: SWR issue  (Read 1615 times)
W1JOP
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Posts: 21




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« on: June 08, 2011, 05:17:28 AM »

Hi,

 I run the FT-897D with LMR 400 and have an SWR issue I can't track down. I thought for a while
that I had a coax issue now I am starting to think it's a antenna problem or a faulty SWR meter on the radio. I have a high SWR below 147mhz and a good SWR 147 and up 440 I have a very low SWR. When a radio has a high SWR do you have a spike on the amps meter on your power supply? IE: high SWR makes the radio pull more amps.

This is only a 2 meter problem

John
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AC5UP
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Posts: 4419




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« Reply #1 on: June 08, 2011, 06:20:30 AM »

When a radio has a high SWR do you have a spike on the amps meter on your power supply? IE: high SWR makes the radio pull more amps.

Nope. Should go the opposite way.

If the reflected power returning to the radio is high enough to pose a threat to the PA transistors the vast majority of radios will fold back the output (reduce power) to protect itself. Reduced power out would likely result in a reduced power draw from the power supply.
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K0BG
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« Reply #2 on: June 08, 2011, 06:21:46 AM »

What you describe doesn't make sense, unless there is a large amount of common mode current. What is the antenna? A J-pole maybe?

As for the current draw, shouldn't make much difference whether the SWR is high or not. Until the radio folds way back (!), the collector current won't change very much.
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K7RBW
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« Reply #3 on: June 08, 2011, 06:33:27 AM »

By definition, the quality of half the advice you see posted in this forum is below average!
I think that "by definition," half the posts would be below the median.

To the topic at hand, could it be that RF is getting into the power supply and causing some unusual readings? Can you move the power supply or ground it, perhaps to see if the readings change? Perhaps put another meter in the circuit to verify the reading? I have a voltmeter that goes all whacky when I transmit, however, I haven't attributed that to SWR, per se.

Does this happen in other situations like with reduced output power?
« Last Edit: June 08, 2011, 06:39:06 AM by K7RBW » Logged
KE3WD
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Posts: 5689




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« Reply #4 on: June 08, 2011, 07:34:16 AM »

Your first step should be to replace the antenna with a good 50 ohm dummy load at the same connection and see what the results are.  This should help with isolation of the situation, which is what you need to do first.  The dummy load can tell you if the problem is going to be with the antenna/feedline or if it may be in the rig or metering. 

Isolate. 


73
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G3TXQ
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Posts: 1792




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« Reply #5 on: June 08, 2011, 09:03:04 AM »

By definition, the quality of half the advice you see posted in this forum is below average!
I think that "by definition," half the posts would be below the median.

I've been wary of averages ever since I discovered I have more than the average number of legs for a human being Wink

73,
Steve G3TXQ
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WD8T
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Posts: 259




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« Reply #6 on: June 08, 2011, 10:10:22 AM »

Hi,

 I run the FT-897D with LMR 400 and have an SWR issue I can't track down. I thought for a while
that I had a coax issue now I am starting to think it's a antenna problem or a faulty SWR meter on the radio. I have a high SWR below 147mhz and a good SWR 147 and up 440 I have a very low SWR. When a radio has a high SWR do you have a spike on the amps meter on your power supply? IE: high SWR makes the radio pull more amps.

This is only a 2 meter problem

John

We know theres an FT-897D on one end of  that LMR-400, soooo what's in between and attached to the other end?
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AC5UP
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Posts: 4419




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« Reply #7 on: June 08, 2011, 11:01:31 AM »

I think that "by definition," half the posts would be below the median.

It's a joke, and "average" plays funnier than "median".
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W1JOP
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Posts: 21




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« Reply #8 on: June 08, 2011, 01:51:54 PM »

Thanks for the reply, I have a dummy load that I gotta pick up tomorrow and this weekend I am going to do some serious testing. I have a diamond tri-band antenna, becuase this issue is only happing on freqs below 147.000 I am leaning twords a fault with the antenna, so first is I plan on running the dummy load with the coax if its high then ill try at the radio. I will be a bit angry if I find its a problem with the coax, I really hope its not
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KB4QAA
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Posts: 3257




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« Reply #9 on: June 08, 2011, 02:21:50 PM »

What model SWR meter are you using?   How long is your coax run?   
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W1JOP
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Posts: 21




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« Reply #10 on: June 08, 2011, 02:31:54 PM »

The FT897D has a meter built in that you see on the display so i am going off of that one, I have a 60foot run of LMR400
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