[Elecraft] Antenna Analyser - Phase Angle Sensor

[Larry Phipps]

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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