[Elecraft] Sudden jump in SWR when power above 80 watts

[goldtr8 at charter.net]

Sounds like my shack when I had RF problems.  Strange SWR was one of my 
problems also.

One thing I found is that I need to wind a big choke on the power leads 
into the K3 to stop a lot of my problems.  It was the last thing I did 
to fix issues.  I wish I would have know to start there :-)

~73
Don
KD8NNU


On Sat, Feb 18, 2012 at 6:09 PM, Ken wrote:

> On Feb 18, 2012, at 5:43 PM, Don Wilhelm wrote:
>
>> Rick and all,
>>
>> Look for something in the antenna system that is arcing over above 
>> the 80 watt level (or whatever level the problem starts).  Check 
>> every junction in your antenna system.  Your workaround may be OK, 
>> but the real fix may increase your antenna efficiency.
>
>
> That's where I first started.  I replaced the ancient twin lead with 
> new open wire.  No change.  I replaced the 4:1 balun with a new 1:1 
> balun.  No change.
>
> I replaced the coax to the balun.  No change.  I inspected the center 
> insulator, that's a block of quarter inch PVC with everything 
> separated at least two inches.  I checked the end insulators.  They 
> look fine and they are tied to Dacron line.   The ONLY thing I didn't 
> change is the antenna wire ;-)
> The antenna is in free space with the closest object being the antenna 
> mast a foot away.
>
> What did stop the problem is changing rigs (to a TS-440) or changing 
> the antenna tuner (to the Palstar).   What's in common with the 
> problem?  The K3.
>
>
>>
>> The other situation that will cause "bad behavior" above a certain 
>> power level (and on a particular band) is common mode RF coming in 
>> from the antenna and its feedline.  The SWR sensing circuits may "go 
>> crazy" in the presence of too much RF voltage.  In this case, the use 
>> of common mode chokes at the antenna, and possibly at other points 
>> along the feedline may be what it takes to "tame the beast".
>
>
> Now that sounds like a possibility.
> Ken WA8JXM
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