Hi Gary.
If that is the case , it still is valid to use the Smith Chart with a zero line
length .
It has been a while since I played with one so I didn't dig it out an go
through it.
I believe you start by normalizing the chart as some are set to 50 ohms and
some are set
to 1 as a factor for any impedance.
If this is so , then it would seem that you line section is set to 1000 ohms
and the
connection element is running at that impedance.
Bill made a point that the current to voltage ratio is set when the load
impedance is 50
ohms and that is where the current and voltage pickups in the Bird(tm) meet
equal pickup
to null an in phase load when measuring reflected power. Even though your load
is in
phase , the coupling of voltage and current are not equal at 1000 ohms and so
you
reading are the sum and difference of the pick-up from those magnitudes.
---
Ron
Gary Schafer wrote:
> Ron wrote:
>
> > > <snip>
> > > I don't think that is right. I did another test with the same setup but
> > > this
> > > time I used only a 1000 ohm resistor for a load and no capacitor.
> > >
> > > Transmitter--watt meter--tuner--drake watt meter-- 1000 ohm load resistor.
> > >
> > > By adjusting the tuner for zero reflected power on the first watt meter
> > > that
> > > leaves the drake watt meter and a 1000 ohm resistive load that should have
> > > no reflected power.
> > >
> > > With 20 watts indicated on the first watt meter the drake watt meter
> > > showed
> > > about 100 watts forward and about 80 watts reflected. The difference in
> > > forward and reflected readings is the power delivered to the load. But
> > > there
> > > should be no reactive component in the load in this setup. There should
> > > not
> > > be any reflected power from the load. There should be no "apparent power".
> > >
> > > The reading of high forward and high reflected power on the meter has to
> > > be
> > > meter error when not operating at the design impedance.
> > >
> > > This brings us back to the question of how do we determine how much
> > > reflected power we have, if any, when looking at a watt meter?
> > >
> > > In this case with the 1000 ohm resistor there should be no reflected power
> > > in the circuit. This indicates a gross error in the meter reading.
> > >
> > > 73
> > > Gary K4FMX
> > >
> >
> > Hi Gary.
> > The output side of the tuner looking into the resistive load is reactive
> > and is
> > determined by the line length , velocity factor and frequency.
> > If you have a reference on Smith Charts, you will see that one can
> > transform an
> > impedance using a length of transmission line.
> > One can also cancel the reactive component of an antenna by using the same
> > technique and change the impedance into a pure resistance.
> > If the line impedance were 1000 ohms (and the resistor is non-inductive),
> > then
> > there would be a resistive load at the tuner , all frequencies , all line
> > lenghts.
> > If it is any other impedance , then there are standing waves on the line
> > and the
> > impedance at the tuner revolves around a circle on the Smith Chart known as
> > a
> > Circle of constant SWR and is determined by the position of the line length
> > to
> > the tuner. It repeats itself every electrical wavelength and is purely
> > resistive at two positions only.
> >
> > Voltage magnitude times Current Magnitude is Apparent power and is composed
> > of
> > Real Power (Watts)and Reactive Power (VARS) . The real power is Includes
> > the
> > phase angle between I and V . Reactive is whatever is left.
> > ---
> > Ron
> >
> >
>
> Hi Ron,
>
> Yes I would agree with you if there was a transmission line involved. But in
> this
> test the load resistor is connected directly to the watt meter no line
> involved.
> Between the tuner and the watt meter I first had about 3 feet of line. I then
> eliminated that and connected the watt meter directly to the tuner. No line.
> The
> watt meter read the same with or without the 3 feet of line from the tuner.
> Slight
> adjustment of the tuner without the line. I tried this on 20 meters and on 80
> meters with the same readings on both bands. I first used a 5 watt 1000 ohm
> metal
> film resistor for the load. I then replaced it with 3 parallel carbon
> resistors to
> make 1000 ohms. The readings were the same. There may be a small amount of
> reactance in my connections but the fact that I get the same readings on 80
> and 20 I
> would think pretty much eliminate any reactance being a factor.
>
> 73
> Gary K4FMX
>
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