Re: my KPA1500 and 160M

Posted by David Gilbert-2 on Sep 02, 2020; 11:35pm
URL: http://elecraft.85.s1.nabble.com/OT-WWV-Time-Transmissions-tp7664561p7664629.html


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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