[Elecraft] NOT the feedline (was KPA-1500 faulting on 6m; SWR issues)

[David Olean]

Hello Peter

I suspect RFI as well. I do not have a KPA1500, so my advice is not 
worth much, but the fact that the fault only occurs when a signal is 
being radiated sends me a red flag.  I had a similar problem here with 
my SPE amplifier power output. I was measuring it on an LP-100A 
wattmeter.  It turns out that 1.8 MHz energy from the SPE amp radiated 
from my vertical antenna and  was getting into a new wire doublet 
antenna and coming back down the ladder line into the shack. The ladder 
line was about 7 inches from the power coupler for the LP-100A. RF 
caused the readings to go wacky and it looked like my amplifier was 
going postal!  The problem was high rf fields next to the power meter 
coupler.

Ferrite balun heating can be seen with a VSWR meter if you set the power 
at some intermediate level, key the amp up with a steady carrier, and 
watch for VSWR creeping up.  Loose pins in coax can also be a problem. 
They can heat up and disconnect or start arcing. Those problems do not 
typically show VSWR creep. They happen all at once usually.

The KPA1500 works fine into a dummy load. (No RFI)  That is a big 
clue.   Good luck and I hope you find the problem. Maybe an RF sniffer 
would detect the ingress point?

73

Dave K1WHS


On 6/1/2020 5:24 AM, Eric Norris wrote:
> Is there any chance RF is getting in to the KPA1500 via an alternative
> route, like one of your HF antennas, a faulty switch, loose bonding/ground,
> or even a change in house wiring or wifi router, antenna rotator cable,
> picking up the RF and radiating/routing it to the KPA1500 from the
> antenna?  It's a shot in the dark, I know, but cut out everything but the
> direct signal path originating from the K3, pull all the house breakers not
> used, turn off everything--make only the 6m path active and see what
> happens if this makes sense to you.
>
> I feel your frustration--the same thing in reverse took out my 2m EME
> station. I replaced every single thing, sent the K3 to Elecraft, the XV144
> to Don...GUD LUCK OM!
>
> VY 73 Eric WD6DBM
>
> On Sun, May 31, 2020, 9:07 PM Peter Dougherty <lists at w2irt.net> wrote:
>
>> New coax and old coax behaved identically. HOWEVER, running into about 80
>> feet of old RG-213 and into the Cantenna dummy load and it doesn't fault.
>> This is the only condition on 6m where there is no fault. Brand new coax,
>> old coax, brand new antenna, old antenna, with balun, without balun. Always
>> faults except when feeding the pure resistive dummy load. If there's any
>> reactance it trips or gives false SWR info.
>>
>> I would also add, why would a 2:1 SWR trip out the amp at 25 or 30 Watts
>> of drive? On the regular HF bands I can use the internal tuner to take out
>> a 2.5 or 3:1 SWR and it still sends 1400-1450 Watts up the pipe..
>>
>>   - pjd
>>
>> -----Original Message-----
>> From: Adrian <vk4tux at gmail.com>
>> Sent: Sunday, May 31, 2020 11:05 PM
>> To: Peter Dougherty <lists at w2irt.net>; 'Paul Baldock' <
>> paul at paulbaldock.com>; elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] NOT the feedline (was KPA-1500 faulting on 6m; SWR
>> issues)
>>
>> To remove any doubt, a 1.5kw or close dummy load at the end of the coax to
>> replace antenna, would confirm the amp issue.
>>
>> On 1/6/20 12:27 pm, Peter Dougherty wrote:
>>> Paul, please re-read what I wrote. The 90W figure is with the amp IN
>>> STANDBY! I wouldn't dream of putting more than about 35W into the
>> KPA-1500.
>>> I generally like to run about 1200W on 6m, but even if I turn my K3s
>>> drive down to 20 Watts, it will STILL hard-fault regularly. NO AMOUNT
>>> OF DRIVE from the K3s will stop these problems. If the amp is set to
>>> deliver power it's going to fault on 6m, regardless of what the ATU is
>>> set for (bypass or inline), and the KPA will miss-read the SWR of the
>> antenna system.
>>> The resistance figure is 50.8 Ohms, and the reactance is -11 according
>>> to the AA-230. The only difference between "works reliably" and
>>> "faults out all the time" is one is a resistive-only load, the other
>>> has a reactive component.
>>>
>>>    - pjd
>>>
>>> -
>>>
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