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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