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

Sun May 31 21:38:13 EDT 2020

Balun? Is it new? What kind?
You have pretty much eliminated the KPA1500 with this test. This sounds like a balun toroid heating up and causing problems. 
You will see perfect conditions at low power, and the AA230 will also show things in great shape. They are not stressing the system. But 1500 watts sure will.
Talk a better look at the antenna system. And the balun. Open it up if possible.

And, again describe, in detail the antenna system. There is something there to be found.

73!
Jack, W6FB

> On May 31, 2020, at 6:29 PM, Peter Dougherty <lists at w2irt.net> wrote:
> 
> Many here suggested that it was most likely a feedline issue, and I figured
> this was indeed a distinct possibility. 
> 
> So this afternoon I replaced the feedline. I now have about 80 feet of brand
> new LMR-400, new 83-SP1 connectors (and an Amphenol adaptor at the balun
> since I don't have any type-N connectors here). The AA-230 ZOOM analyzer
> shows about 1.2:1 at 50.313, with resonance just below the band. I'll fix
> that tomorrow, but 1.2 or 1.3:1 should be nothing to the KPA. 
> 
> The TDR screen looks very clean, just a tiny bump where the feedline goes
> through the (new) bulkhead connector to get into the house. See:
> https://www.dropbox.com/s/izcwvece7nt5f42/2020-05-31%2019.32.44.jpg?dl=0
> 
> The SWR chart between 50.000 and 50.500:
> https://www.dropbox.com/s/y2xh4l1lihy2ujr/2020-05-31%2021.23.29.jpg?dl=0
> 
> Again, I know the antenna is resonant a bit low, but this should NOT be a
> factor. So here's what's now going on.
> 
> 1) Into a Cantenna dummy load, with 25W of drive from the M3s, the KPA-1500
> is delivering 1075W and showing 1.4:1. No problem delivering power and no
> faults.
> 
> 2) With input power increased, 35W of K3s drive gives 1375W at 1.5 into the
> Cantenna. Again, no problem delivering power to the purely resistive load.
> Why a 1.5:1, I don't know, but fine, whatever. I can TX for 15-20 second
> periods without issue.
> 
> 3) When I switch over to the live antenna, with25 Watts of drive from the
> K3s into the actual antenna and the amp faults out instantly in bypass. When
> the amplifier is in bypass and the tuner is in bypass, and when the K3s is
> delivering about 90W in FT8 mode, the front panel on the KPA-1500 says the
> SWR is 1.9:1. When I press the TUNE button on the radio, it's showing an SWR
> of 1.4:1. 
> 
> 4) Amp in bypass, tuner inline, press TUNE button on the K3s and the front
> panel of the KPA-1500 is showing a perfect 1.0:1 match. It SHOULD work fine
> like this, right?
> 
> 5) Pressing ONLY the OPER/STBY button to put the amp in operate (KPA tuner
> in and untouched since step 4), the amp SOMETIMES delivers power, sometimes
> faults out, shows an SWR of 1.7:1. Pressing the OPER/STBY button again to
> use only exciter power, and touching NOTHING ELSE, it's back to 1.1:1 with
> 90W of K3s drive.
> 
> 6) There is basically no rhyme or reason why this is happening and it's
> *somewhat* repeatable. The incredibly frustrating part is if I see a needed
> station come up, I'll flick the amp's tuner in line and it says it's tuned.
> Once WSJT-X keys the radio, 90 out of 100 times the amp will hard-fault. If
> it doesn't fault on the first transmission, it absolutely WILL on the second
> transmission. 
> 
> So I'm now at a complete loss to understand what's going on here. Amp is
> fine into a resistive load. Brand-new antenna, brand new LMR-400 feedline,
> brand new connectors, the KPA-1500 is faulting out the same as it did on the
> 10+ year old 6M5 with a patchwork of feedlines. I can't see how this is
> anything but a problem in the KPA-1500 (S/N 0398).
> 
> - pjd
> 
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On
> Behalf Of Jim Brown
> Sent: Sunday, May 31, 2020 8:22 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] KPA-1500 faulting on 6m; SWR issues
> 
> On 5/31/2020 9:54 AM, Jim Miller wrote:
>> Have you vetted your feedline at 1500w? Many times something might be 
>> good at low power and fail at 1500.
> 
> This is good advice. Guys who do lots of portable setup say to always check
> the coax first, which mostly means check for a connector that's bad or badly
> installed.
> 
> In general, if it doesn't say Amphenol or isn't stamped with a MIL spec
> number, it's very likely to be poor quality. This includes barrels,
> adapters, etc.  Also make sure that every connector is" wrench tight."
> 
> The advice to run it straight to a dummy load is right on -- if you have one
> big enough. :)
> 
> 73, Jim K9YC
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html Message
> delivered to lists at w2irt.net 
> 
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to jackbrindle at me.com 