[Elecraft] KXPA100 Intermittent VSWR Issues

[Matt VK2RQ]

It's not just that, a varying signal can also cause the amp's internal frequency counter to misread your current frequency. If the amp thinks you moved frequency, it can tickle the ATU. The "frequency counter inertia" adjustment in the latest firmware addresses this issue very effectively, and my amp/ATU has been a rock-solid performer since loading that latest KXPA100 firmware release.

73,
Matt VK2RQ

> On 9 Dec 2014, at 7:01 am, Cady, Fred <fcady at ece.montana.edu> wrote:
> 
> The SWR circuitry in the KXAT100 (and KAT500) measure the forward and reverse voltage values at different times.  They cannot be measured simultaneously because they don't have dual A/D converters or sample-and-hold circuits.  To be sure, there is only a short time between sampling the forward and reverse directions but if your output power is changing with time as it will with a high speed CW signals and more especially and more troublesomely with a SSB signal, the SWR metering may indicate an incorrect value.  If you have the tuner in AUTO mode, this may trigger a retune. For this reason it is best to operate either of these tuners in MAN mode and train the tuner(s) to store good L-C values for different frequencies in each of your operational bands.  The tuners store this information in "frequency buckets" and when they detect the frequency within that bucker they recall the L-C values and if they need to be changed they will be.
> 
> Summary:
> Train the tuner so that it can remember the L-C values to use for a specific range of frequencies.
> Don't use AUTO mode;  use MAN mode.
> 
> Cheers and 73,
> Fred KE7X
> "The Elecraft K3: Design, Configuration and Operation 2nd ed"
> "The Elecraft KX3 - Going for the summit"
> "The Elecraft KPA500 and KAT500 - the K-Line Dream Station"
> Printed, coil bound copies of these are all available at www.elecraft.com
> KPA500 and KAT500 Quick Set Up Guide
> http://www.ke7x.com/home/k-line-introduction-and-set-up-guide
> 
>> -----Original Message-----
>> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
>> Jim Kutsch, KY2D
>> Sent: Monday, December 08, 2014 9:18 AM
>> To: Elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] KXPA100 Intermittent VSWR Issues
>> 
>> I'm experiencing the same thing but mostly on 40 meters where the best
>> match with the ATU isn't as good as on other bands. It *SEEMS* to have
>> started Saturday when I installed the latest KX3 beta and set
>> compression to 20. The antenna is a Carolina Windham.
>> 
>> 73, Jim, KY2D
>> .
>> 
>> 
>> -----Original Message-----
>> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of
>> Jim Stahl via Elecraft
>> Sent: Sunday, December 07, 2014 10:08 PM
>> To: elecraft at mailman.qth.net
>> Subject: [Elecraft] KXPA100 Intermittent VSWR Issues
>> 
>> I've run into several occasions where in mid-CW transmission my KXPA100
>> (with internal tuner) SWR takes a momentary jump from matched to maybe
>> 3:1.
>> I see the SWR jump on both the KXPA front panel LEDs and on  the KX3
>> VSWR display.  It lasts for maybe half a second, I hear  several clicks
>> of the relays in the tuner, and them it's back to normal. When  normal
>> the SWR is pretty much 1:1 on the KX3, and the second green LED lit on
>> the KX3. I've not seen it happen at the start of a transmission, but
>> rather several characters into a CQ or exchange..
>> 
>> In the ARRL 160 contest Saturday night this was happening perhaps once
>> every
>> 2-3 minutes. I'm using a fairly well matched antenna - not random
>> wires.
>> I  also encountered this problem on 15 meters when operating from
>> W1AW/8 in WV  in October. In both cases I was running a pretty high CW
>> duty cycle while  running at a pretty good clip. The amp was warm, but
>> the heat sink air flow is not blocked.
>> 
>> Any thoughts?
>> 
>> 
>> 73  -  Jim  K8MR
>> 
>> 
>> 
>> 
>> ______________________________________________________________
>> 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 jim.kutsch at ky2d.com
>> 
>> ______________________________________________________________
>> 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 fcady at ece.montana.edu
> ______________________________________________________________
> 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 matt.vk2rq at gmail.com