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

[Bob McGraw K4TAX]

Some baluns offer good common mode current rejection while others offer 
virtually no common mode rejection.   {See DJ0IP site and discussion on 
baluns.}  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
>>>
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