> Agreed that the harmonic levels into real-life antennas
> would be
> different again, and even harder to predict... but the
> regulatory tests
> are
> into 50 ohms.
>
In the USA the bottom line regulation is we are not allowed
to have any emission, no matter what level, that causes a
problem.
This is why Novices commonly received warnings or citations
for out of band harmonics. If the FCC can hear it and
decides it is a potential problem you are obligated to fix
it even if it meets all test criteria. They also worked that
way with BC stations. We had an FM station that was half the
frequency of a local VHF TV channel's video carrier. Even
though well over 100dB down on the second harmonic, we were
obligated to shield and suppress until the problem went
away.
But it is true that the requirement is to only test into 50
ohms.
All that aside most class AB PA's with a reasonable tank
layout and reasonable tank Q will have no problems meeting
the minimum requirement under test conditions. As you point
out (via the link) harmonics are all over the place
depending how the tank is wired and how the components are
mounted. One of the least important things are inductor's
position with respect to the cabinet or chassis. Much more
important is capacitor mounting (ground path impedance),
lead routing from the tube to the capacitor, and how the
output lead is taken out of the PA compartment. With a pi-L
mutual coupling between the L coil and the early parts of
the tank is very important.
73 Tom
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