In KP3MM's recent post he reveals that the problem doesn't occur with
his Clipperton amp at one KW, so it appears that the problem is indeed
within the KPA1500. But to be clear, he never said that the problem is
there from the start. In his recent message he says that it takes 15 to
30 seconds for the amp to trip.
In addition, your statement that only current in the balun circuit can
produce heat is completely false. High voltage RF can create major core
heating due to dielectric losses in the ferrite core independent of the
magnitude of current flow in the tuning circuit. Several discussions on
the TowerTalk reflector have pointed this out over the years for baluns
and common mode chokes in ham radio applications.
Dave AB7E
On 9/2/2020 3:55 PM, Adrian wrote:
The problem is evident on first KPA1500 match attempt before any
heating of the balun core is possible. It is not a core heat issue at
all.
If it was the OP would be able to get an ok initial atu match, that
would then deteriorate with core heat..The issue is from the get-go.
Also only current in the balun circuit produces emf and therefore
core heat. Voltage is only a factor in how much current flows depending
on circuit impedance, Plenty of voltage with no current = no heat.
On 3/9/20 3:25 am, David Gilbert wrote:
More likely that the ferrite core is getting hot from excessive
VSWR. High current could, but rarely does, heat up the coil, but
it's high voltage which often heats up the core. At low power (and
therefore low VSWR voltage) it wouldn't necessarily be a problem, but
at high power it easily could. I know this from personal experience
with a 160m Inverted-L that initially had a high VSWR that with high
power heated up a MUCH better common mode choke (homebrew per K9YC
guidelines) than the Balun Designs stuff.
73,
Dave AB7E
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