Re: High SWR on all HF Bands


Dennis Klipa
 

That is a curious problem and I look forward to hearing the resolution. 

I tend to agree with William.  SWR is independent of where you measure it along a length of coax.  There are two exceptions to this rule.  One is when the coax is very lossy and power is consumed in the line during the trip to the antenna and back resulting in less reflected power and an apparently better SWR and antenna match than is reality.  I once used some new Radio Shack RG58 to connect to a 2 meter vertical.  I had a perfect 1:1 SWR.  The only problem was that no rf was actually making it to the antenna and so nothing was reflected!  The second exception is when you have rf voltage on the outside of the coax.  In that case the SWR reading will vary with position along the coax, but you are not reading true SWR.  This situation usually arises with unbalanced antennas or systems.  As William suggested, common mode chokes can rectify that problem.  

I do have a question.  Do you always have the external power/SWR meter in the line or was it there just to explore the problem?  Does the problem exist without the external meter?  If it is always in-line it could be the source of the imbalance.  Does the IC7K SWR reading change if you replace the external meter with a barrel connector?

If you don't have rf on the shield of the coax, and assuming that a defective part in the IC7K has caused a calibration issue of the SWR meter, I would not expect to see the SWR vary with coax length.  But, I have been wrong before.

Happy hunting!

Best Regards,
Dennis, N8ERF


On Wed, Oct 28, 2020, 2:04 AM William Kerker <km0f@...> wrote:
I'm wondering if you need a common mode choke on the coax. Sounds like RF on the coax. 

On Tue, Oct 27, 2020 at 8:13 PM Max via groups.io <kg4pid=yahoo.com@groups.io> wrote:
Hello everyone. I have an Icom 7000 that now shows a high SWR (2:1 - 3:1) depending on band into a dummy load (2 different ones). Here's the catch, I can change the SWR by using different lengths of coax between the radio and my external power/SWR meter. My external meter shows my dummy loads to be a good match but the radio doesn't agree. For a few months now I've had to use a 25Ft RG-58 jumper just to keep the SWR around 2:1 on the radio.

Is this just some failed part in the SWR detection circuitry or do I have bigger problems. I know its just guessing but what are the chances of it being an easy repair and are the parts available?

I'd hate to send it in just to be told the parts are unobtainium.

Max KG4PID



--
Bill,  KMØF

Radio Amateurs must be tough, it's a 'Contact Sport'

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