[Elecraft] KPA1500 - temp reading drops 10C when under power

[Paul Baldock]

I just checked mine on 40M and when on CW Temp is 
bouncing all over the place. Same into a dummy 
load as the antenna 300ft away. It also does it 
to a lesser extent on 80M and a little bounce on 17M and 10M.

I suspect its in the amp and not related to common mode RF in the coax.

Probably a cap in the right place would fix it.

- Paul


At 11:20 AM 8/18/2018, you wrote:
>Some baluns offer good common mode current 
>rejection while others offer virtually no common 
>mode rejection.   {See DJ0IP site and 
>discussion on baluns.}Â  Since the feed line 
>from the balun runs down the tower to the point 
>where the feedline runs underground, that 
>segment of feedline is exposed to radiation from 
>the antenna.  Certainly common mode current can 
>be a very realistic occurrence in this case. 
>..........." it's some sort of new 
>hyper-super-ultra-infina-deluxe type never 
>before discovered on earth."   Nope,  it is 
>just basic physics regarding the properties of 
>RF induced currents.    Depending on band, a 
>choking impedance of 300 to 5000 ohms may be 
>needed to resolve the issue.   Since it was 
>disclosed as power related, this supports the 
>issues of common mode currents. Good luck in 
>finding and correcting the matter. 73 Bob, K4TAX 
>On 8/18/2018 12:20 PM, Jeff Blaine wrote: > Odds 
>are not good there.  The antennas have a balun 
>at the feedpoint, > are on a tower 500 feet from 
>the shack and the hardline runs under > 
>ground.  If there is common mode involved, it's 
>some sort of new > 
>hyper-super-ultra-infina-deluxe type never 
>before discovered on earth. > > 73/jeff/ac0c > 
>alpha-charlie-zero-charlie > www.ac0c.com > > On 
>18-Aug-18 7:12 AM, Bob McGraw K4TAX wrote: >> 
>I'd say a bit of common mode current on the feed 
>line.    I see that >> from time to time with 
>my KPA500 on certain bands/antennas. >> >> 
>73 >> >> Bob, K4TAX >> >> >> On 8/17/2018 11:45 
>PM, Jeff Blaine wrote: >>> While running the 
>KPA1500 in the SARTG tonight, I noticed that 
>the >>> temp reading drops about 10C when 
>transmitting.  min fan speed 1. >>> >>> Seems 
>to be related to power - at 1500W it's pretty 
>close to 10C. At >>> lower powers, it's less of 
>a difference.  I don't recall seeing that >>> 
>before. >>> >>> Normal? >>> >>> 73/jeff/ac0c >>> 
>alpha-charlie-zero-charlie >>> 
>www.ac0c.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 rmcgraw at blomand.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 keepwalking188 at ac0c.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 rmcgraw at blomand.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 paul at paulbaldock.com