[TowerTalk] SWR is what SWR meter measures

[mofolk]

Too All the SWR Buffs ...

Being extremely well versed in the mathematical physics of transmission
lines, having spent years
in measurement and lots of practical verification and now watching all the
debate (for the 2765th time)
as to what is measured and what it means ... I have resisted until I can no
more ...

The entire matter is settled once and for all ... when you discover that

SWR does not stand for         See What Returns          but clearly

stands for            SPEED   WEIGHT and  RATIO ....


Now,  CALL CQ, the IONS are waiting!   Amen!

.. de dave w7fb

----- Original Message -----
From: "Martin, AA6E" <martin.ewing at gmail.com>
To: <garyschafer at comcast.net>; <towertalk at contesting.com>
Sent: Friday, May 13, 2005 10:08 AM
Subject: Re: [TowerTalk] SWR is what SWR meter measures


> Gary,
>
> An impedance mismatch is the same thing as a reflector.  How do you
> think mirrors work? It's a matter of perspective.
>
> "Reality" of power flow is debatable.  Let me describe it from my
> viewpoint as someone brought up as a physicist.
>
> The basic issue is what are the voltages and currents in your system
> at each point?  "Power" only has tangible meaning when it is delivered
> somewhere in a useful form (e.g., heat).  Otherwise, it's a
> mathematical construct - a way of doing the accounting to make sure
> energy is conserved. On your transmission line, there is voltage and
> current at each point, which are described by differential equations
> and boundary conditions. (Ultimately, Maxwell's equations.) If you
> have a match, V and I are uniform along the line.  If not, you have a
> standing wave.  (No issue of "power" yet.)  The forward/reverse power
> numbers you measure from samples of V and I on a transmission line
> turns out to be useful in controlling transmission line losses (and
> possible over-current and over-voltage conditions) and for maximum Tx
> output.  In some cases (TDR) it is easy to relate forward and reverse
> power to a particular "piece" of energy - a wave packet, and an
> impedance mismatch is recognizable as a mirror - a source of reflected
> energy.
>
> In the extreme, our arguments here resemble the wave/particle debates
> in physics.  Sometimes electrical signals behave more like particles
> (radar, TDR), sometimes more like waves (CW network analysis). Neither
> description is wrong.
>
> An aside:  I am annoyed by tuners and switches and other items that
> are rated for "power handling" capabilty.  E.g., a 1 kW balun.  These
> devices don't care about power, except they will have a thermal
> dissipation limit.  They care about voltage and/or current.  At 50
> ohms, the power level tells you V and I, but if you have anything
> other than 1:1 SWR at 50 ohms, V and I can be very different.  So you
> see "1 kW" baluns burning up at 100 W power levels, etc.
>
> This is a never-ending discussion, as someone pointed out at the
> beginning of the thread.  It's very interesting, but the connection to
> "towers" is not very clear!
>
> Cheers
> Martin AA6E
>
> On 5/13/05, Gary Schafer <garyschafer at comcast.net> wrote:
> >
> > Here is another way to look at it: With a circulator at the transmitter
> > output and a load on the return port of the circulator, disconnect the
> > antenna line from the circulator. Now all the power out of the
> > transmitter goes into the load on the circulator and the transmitter
> > still sees a flat 50 ohms.
> >
> > Is there really reflected power involved or does the power get dumped
> > into the load because of an impedance mismatch at the antenna port on
> > the circulator?
> >
> > We could look at reflected power not even existing on transmission lines
> > at all. In fact we could look at it as once the transmission line is
> > initially charged at transmitter turn on there are no more reflections.
> > What we see are only impedance mismatches that our meters are showing
> > us. As others have pointed out the swr bridge or watt meter is not
> > really showing power but the indication is the result of an impedance
> > mismatch from the value that the meter was calibrated for.
> >
> > 73
> > Gary  K4FMX
> >
> >
>
>
> --
> martin.ewing at gmail.com
> http://blog.aa6e.net
> _______________________________________________
>
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>
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