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Author Topic: Icom 703 plus ATU Question / Help  (Read 929 times)
WB7TSO
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Posts: 34




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« on: March 20, 2013, 02:10:05 PM »

I thought I'd start here with my question and move off to repairs or QRP if no one has a quick and easy answer. I recently purchased a used 703+ and was finally able to get up my Cushcraft R6000 vertical. I tuned the antenna up with my analyzer to a SWR of around 2:1 worse case  - 1:1.2 best. Well the 703 ATU was very unhappy and I was only able to keep the red led on Tune with 17m and 15m initally. So I reset the ATU memory and now I get 12,15,17 but no 20,10, or 6m. I figured I'd have to pull the vertical down and retune it. So as an experiment I unpacked my IC-746 PRO and low and behold it tuned the antenna on everything even 40m seem to work go figure? So here's my question " Is the 703 ATU extremely sensitive like one reviewer said or does my unit have an issue?" Because if you read the Icom manual they are both able to tune the same SWR mis-match.

Thanks Brad WB7TSO
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W2AEW
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« Reply #1 on: March 20, 2013, 07:08:07 PM »

First thing I'd check is ground connections, etc.  that being said, the 703 tuner should be able to handle that.  I've never had a problem with the 703's tuner, even when the untuned SWR was 3:1 or sometimes worse.  Yours might have an issue.
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WB7TSO
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Posts: 34




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« Reply #2 on: March 21, 2013, 02:44:20 PM »

Thanks for the help. I had a great conversation with Steve at MTS. He suggested that I reset the tuner and check the SWR at 14mhz. If the radio is seeing a high SWR it will fold back the power. This is regardless of how good my antenna is tuned.

He also recommended that I follow the service manuals instructions on reseting the tuner relays. Hopefully this helps anyone out there who finds this post at a later date.

He made it clear that the 703 has very little RF power to work with so that is why it is harder to find a good tune (impedance and reactance) as where the Pro has 3 variables and a lot more RF power hence the difference.

73's Brad Smiley
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WA3SKN
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Posts: 5555




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« Reply #3 on: March 22, 2013, 05:51:30 AM »

What do you get when transmitting into a known good dummy load?

-Mike.
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WB7TSO
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Posts: 34




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« Reply #4 on: March 22, 2013, 08:10:59 AM »

As this unfolds further. I think I have some bad band pass diodes since. My SWR on 20m & 10m is just fine according to the rigs internal meter but it still wont tune. According to Steve at MTS the 703 can still receive even with a few bad diodes. I'm still digging into the rig. I'll post a full report once I have it solved.

Also I need to get a dummy load to test it better at present I'm minus a watt meter and dummy load (working on that)

 Thanks

Brad WB7TSO
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WB6BYU
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Posts: 13573




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« Reply #5 on: March 22, 2013, 08:36:16 AM »

Brad -

Drop me a note:  I may have one you can borrow if needed.

My callsign at ARRL dot net.
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