Gary, I think what Tom was suggesting is that the
meter can still be used to reliably determine power
delivered to the load even with large impedance
mismatches. Also, it would appear that the reflection
coefficient of the load can still be calculated from the
absolute meter readings even though these absolute
readings start to lose their physical significance as the
load departs greatly from the design impedance.
In fact, unless you are using a circulator on the output
of the transmitter, the concepts of forward and
reflected power lose their physical significance in
the steady state case. In the steady state case, the
important parameters are the degree of steady
state load impedance mismatch seen by the transmitter,
and the amount of real power delivered to the load.
The wattmeter gives a useful indication of both.
73 de Mike, W4EF...............................
----- Original Message -----
From: "Gary Schafer" <garyschafer@attbi.com>
To: "Ian White, G3SEK" <g3sek@ifwtech.co.uk>
Cc: <amps@contesting.com>
Sent: Thursday, April 04, 2002 2:32 PM
Subject: Re: [Amps] Re: [Amps] Re: [Amps] Re: [Amps] Re: [Amps ] Bird® 43 Ma
nual
>
>
> "Ian White, G3SEK" wrote:
>
> >
> > There are a few loose ends, like the need to prove that it works the
> > same at any position along a transmission line, not just at voltage
> > maxima and minima where E and I are non-reactive... but I'm content to
> > believe that's provable too. Also Maxwell uses a term Zc which he
> > describes as the "line impedance", which doesn't cover the case where no
> > line exists, either inside or outside of the directional coupler... but
> > it still works if Zc is described as the impedance for which the
> > directional coupler was designed (to give zero reflected indication when
> > matched) and at which the power calibration was made.
> >
> >
> >
> > --
> > 73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> > 'In Practice' columnist for RadCom (RSGB)
>
> I just read the original Bruene description and it doesn't give any
> information about open termination's either. He only discusses impedance's
> close to design impedance..
>
>
> Well I just drug out an old Heath HW 101 transceiver. Hooked a short cable
to
> a Drake W4 watt meter and no connection to the output of the watt meter.
> Tuned up on 20 meters. I was able to get the watt meter to read 200 watts
> forward and 200 watts reflected. All this with the plate current on the
> 6146's just a little above the 50 ma idle current. With 800 volts on the
> plates that works out in the neighborhood of 45 watts input to the finals!
>
> Now either I have one hell of an efficient HW 101, to get 200 watts out
with
> 45 watts input, or there is a flaw in this business that the directional
watt
> meter reads properly at all impedance's.
> Yes the net power delivered to the load is zero as the meter would show
> subtracting reflected from forward. However I would conclude that there is
> not 200 watts forward power and 200 watts reflected on the line.
>
> 73
> Gary K4FMX
>
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