[Elecraft] Antenna Analyser - Phase Angle Sensor

[Don Wilhelm]

Larry,

I see no inconsistency with Stuart's statement in your plot.  Without
looking at the specific phase angle - if the absolute magnitude of the
reactance increases with increasing frequency, then the load is inductive,
it it decreases, then the load is capacitive.

The poles of the black curve on your plot do line up with the zero crossings
for the phase.  So if I look at any point on your plot, I see that the
absolute value of the magnitude of the reactance will increase with
increasing frequency anytime the load has positive reactance (inductance),
and the absolute magnitude of the reactance will decrease with increasing
frequency any time the load is capacitive.

Yes, a simple (or complex) phase angle detector working without regard for
the sign will not provide the information required, but 'dithering' the
frequency and looking only at the relative magnitude of the reactance
between 'dither' points can provide the sign of the reactance.

73,
Don W3FPR

> -----Original Message-----
>
> That won't work, Stuart. I wrestled with this for awhile when developing
> my LP-100 Plot program. You also need to know which side of resonance
> you're on, and whether it's a series or parallel resonance... at
> a minimum.
>
> Take a look at the plot at www.telepostinc.com/Files/OCF_Z_PH2.jpg. This
> is a section of an off center fed dipole as measured by my HP 87510A
> VNA. If you take the absolute value of the phase data (ie, have it
> bounce off zero as it would with a meter that can't determine phase
> sign), then you will see the problem. If you look at the phase in this
> plot, starting at the left edge, and remembering that all the negative
> values have to be reversed to look like a meter without sign detection,
> by your definition, the reactance makes the following changes from left
> to right edge...
>
> C, L, C, L, C, L, C, L
>
> In reality, as the VNA shows, there are fewer changes. The sequence is...
>
> C, L, C, L, C
>
> Without the visual aid, it can be confusing, to say the least.
>
> In my Plot software, I take into account a number of  factors, based on
> the slopes of the magnitude and phase of impedance. If you don't do
> this, you could easily be exactly wrong ;-)
>
> 73,
> Larry N8LP
>
>
>
> Stuart Rohre wrote:
> > It is not too simple to measure phase with a additional
> circuitry.  However,
> > it is simple to move the frequency of the antenna analyzer and see the
> > Reactance change,  IF it is increasing with frequency it is inductive
> > reactance, (+); if decreasing with frequency increase, it is capacitive
> > reactance, (-).
> >
> > Once you get used to that, and make a little reminder note to
> paste on the
> > analyzer case, you can do the check easily and remember which type of
> > reactance change you are seeing re frequency.
> >
> > Stuart
> > K5KVH
> >
>
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