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

Mon Jun 1 09:37:10 EDT 2020

Ground loops can be another issue.
I was having a "feed back" issue with my KX3/KXPA100 ans solved it 
eliminating ground/power loops.

73, steve WB3LGC

On 6/1/20 8:25 AM, David Olean wrote:
> 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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