input vs output power

Bill Turner wrt at ESKIMO.COM
Mon Feb 2 23:20:11 EST 1998

On Mon, 2 Feb 1998 19:07:07 -0800, Jeffrey Herman
<jeffreyh at HAWAII.EDU> wrote:

>Why is it that tube xmtrs are rated by input power, and SS xmtrs by
>output power? Is it that SS rigs are expected to be operated into
>a fixed impedance, but no such expectations accompany tube rigs?
>(Of course, that's not true - many tube rigs terminate with an
>SO-239 connector, unless it's a Heath!)
>Jeff KH2PZ (22-year General still asking Novice questions)
Because the FCC changed the rules for power measurement about the time
tubes gave way to transistors.  It used to be that power was the DC
input to the final amplifier, but this got a little messy when it was
realized that the driver in a grounded-grid amplifier also contributed
output power to the antenna, so the rule became output power, period.

Today's rules don't discriminate between tube and SS, so if you're
running a tube rig, you need to monitor output power, regardless of
how the rig was originally rated.

73, Bill W7TI

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