[AMRadio] AM Transmitter Advice??

Bob Bruhns bbruhns at erols.com
Sat Feb 18 19:42:06 EST 2006

Hi Jim... Hmm, it came from my sometimes flakey
memory...  I'm pretty sure there was a 0.25 second spec
for the metering somewhere... maybe it was simply
assumed that the meter time constant would be about
0.25 seconds.  I suppose that if someone came up with a
very slow meter, they could get away with huge SSB PEP,
so it makes sense that the time constant of meter
should be specified at least approximately.

In any event, the FCC proceeded as though the DC volts
multiplied by the DC amps gave the average power
input - which was not true for AM.  This Dc metering
ignored the real power increase during modulation,
permitting the upside down tube loophole.  Now if guys
like me had just kept their mouths shut about it, maybe
the FCC wouldn't ever have caught on.  But no, we had
to throw it in the sidebanders' faces.  I plead extreme
youth at the time.

   Bacon, WA3WDR

----- Original Message ----- 
From: "Jim Wilhite" <w5jo at brightok.net>
To: "Discussion of AM Radio" <amradio at mailman.qth.net>
Sent: Saturday, February 18, 2006 7:28 PM
Subject: Re: [AMRadio] AM Transmitter Advice??

> Bacon, not trying to be contrite, but where in the
old rules did the .25
> second time constant appear?  I have a copy of the
old rules and don't see
> it.  It says only that "have the means".
> 73  Jim
> W5JO
>   At that time, plate power input to an AM
> > transmitter was measured by the reaings of DC
> > with approximately 0.25 second time constant.  That
> > time constant would make the meters read average
> > voltage and current, which smoothed out SSB and
> > controlled carrier signals.  But on plate-modulated
> > it did not read true power during modulation,
> > it was looking at average voltage and average
> > separately, while in AM the voltage and current are
> > separate, but they increase and decrease together,
> > resulting in higher power input during modulation.
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