At 10:29 AM 3/28/2002 -0800, you wrote:
>I would disagree. Power is reflected in a mismatched transmission line.
>Send a short RF pulse down a long transmission line with a mismatch
>at the end, and then switch in a 50 ohm load at the source end before
>the reflected portion of the pulse has a chance to get back to the source.
>The load will dissipate the power in the reflected pulse when it returns
>to the source point. If the you sampled the meter drive voltage on the
>Bird wattmeter with a scope (the meter movement can't respond fast
>enough to read the power in a short pulse), you would see that the
>meter drive voltage with the slug set in the reflected power position
>was proportional to the intensity (e.g. power) of the reflected pulse.
>
>73 de Mike, W4EF............
I sort of thought I said that, though probably not well. Alas, I'm not an
EE, and I'm sure many on the list are. In any event, yes, I agree with your
gedunken results. I think, however, that my argument remains valid even
under impulse analysis. What goes zipping by the meter is a pulse of
voltage and current which are then dissipated as power. At this point, we
may be primarily arguing semantics.
Kim Elmore, N5OP
>----- Original Message -----
>From: "Kim Elmore" <elmore@nssl.noaa.gov>
>To: "AMPS" <AMPS@contesting.com>
>Sent: Thursday, March 28, 2002 9:44 AM
>Subject: [Amps] Re: Bird® 43 Manual
>
>
> > At 11:25 AM 3/28/2002 -0500, you wrote:
> > > > No. Watt meters that hams and most engineers use at RF measure either
> > > > voltage or Current. They do not measure *power*. Given the voltage
>or
> > > > current, analog meters use a graphical conversion (called a meter
>scale) to
> > > > equivalent power given under the assumption of a matched
> > > > termination. Digital meters also perform a conversion in firmware.
>None
> > > > of these devices measure *power*.
> > >
> > >My example is relevant without the need of the Bird wattmeter. I fully
> > >accept the fact that the directional coupler samples RF
> > >voltage. I'll respond to you as I did with Steve. Namely, in the
>absence
> > >of a load on a loss-less line, any and all reflected
> > >power is being absorbed by the fixed-impedance source (i.e., broadband
>PA).
> > >
> > >If reflected power is not absorbed by the source, where is absorbed?
> > >
> > >-Paul, W9AC
> >
> >
> > I believe that the logical flaw in the argument lies in discussing
> > reflected *power*. *Power* cannot reflected; only voltage and current are
> > reflected. We speak of reflected power merely as a convenience because
>the
> > meter we're looking at unfortunately has "power" written on it. In truth,
> > it should say "voltage," so that we could more easily talk about what's
> > really happening. Voltage and current presented to a resistive load,
> > together and in phase, result in "power." We speak of "power" being
> > transferred down a transmission line, but this power is merely a
>construct:
> > the only things that we can measure on the transmission line are voltage
> > and current.
> >
> > Kim Elmore, N5OP
> >
> >
> >
> > >_______________________________________________
> > >Amps mailing list
> > >Amps@contesting.com
> > >http://lists.contesting.com/mailman/listinfo/amps
> >
> > Kim Elmore, Ph.D.
> > "All of weather is divided into three parts: Yes, No, and Maybe. The
> > greatest of these is Maybe" The original Latin appears to be garbled.
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
> >
Kim Elmore, Ph.D.
"All of weather is divided into three parts: Yes, No, and Maybe. The
greatest of these is Maybe" The original Latin appears to be garbled.
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