[Elecraft] KPA500 High Reflected Power Fault

[Dennis Moore]

Sounds similar to what my barefoot K2/100 was doing with an LDG tuner to 
a multiband ladderline-fed doublet. It would tune up alright but as soon 
as I started talking on 17m the tuner would go crazy. I replaced the 
first few feet of feedline with dual coax, grounded the shields. That 
moved the open twinlead a few more feet away from the rig, and it 
presented a slightly different impedance to the tuner. No more problems.

I don't know what configuration you have between the 
tuner/balun/feedline but you might start there.

73, Dennis NJ6G

On 5/15/2011 11:41 AM, n5ge at n5ge.com wrote:
> Sounds to like your LDG Tuner can't match the load...
>
> 73,
> Tom
> Amateur Radio Operator N5GE
>
>
> On Sun, 15 May 2011 11:00:57 -0400, Nels Anderson<nels at flightsim.com>  wrote:
>
>> Been enjoying KPA500 #32 for a couple of days now. Haven't yet made a
>> lot of QSOs with it, but the extra power on RTTY and to bust a couple
>> SSB pile-ups has been welcome.
>>
>> However, the amp does not like my 40m setup. As soon as I transmit it
>> instantly goes into high reflected power fault and shuts down. My
>> antenna is a 120 foot center fed wire using 1 inch ladder line and an
>> LDG 1 kw auto tuner. SWR on 40m is under 2:1 and the K3 and other rigs
>> I've used it with have always been happy with the antenna arrangement.
>>
>> In experimenting I used the K3 tune function and reduced the power in
>> steps to see if I could reach a low enough power level that it would
>> operate, but even at 1 watt of drive the amp still instantly went into
>> fault.
>>
>> On 80m it did the same thing the first time I tried it, but then I
>> manually tweaked the antenna tuner, got a lower SWR reading and then the
>> amp worked. On the higher bands that I've tried there has been no problem.
>>
>> So, any idea what is causing this?
>>
>> 73 Nels K1UR