I am assuming the reflection angle of 0j terminations would all be the same (you
said 180), this includes both resistive loads and an antenna at resonance. The
method I am using relies on that.

I am confused about one thing in the smith chart program. Cables identified as
stubs create a circle that goes through infinity and do not exhibit a constant
SWR, while simple cables create a constant SWR circle with the center and 50 Ohm
0j.

I believe the setup I am testing exhibits the constant SWR characteristic.

Dan

Frank wrote:
"dansawyeror" wrote in message
...

Frank,

Your comment about my post is correct upon analysis it is not relevant.

I am trying to identify the resonance frequency of an antenna. When that
point is found I am trying to measure the input impedance (should be R +
0j).

Assuming 50 Ohm source and cable, the smith chart shows for lengths of
cable terminated in values other the 50 Ohms, say 25R 0j, those points
will plot of a constant SWR = 2 circle. I am using that circle below:

I am assuming that for a frequency where the antenna is resonant that the
phase read from the antenna and the phase read from non 50 Ohm 0j load
will be the same. If that is true then 'zeroing' the meter by adjusting
the phase offset will not effect the frequency of resonance. It is simply
a convenience.

This method should yield a direct resonant frequency reading.

Dan


Dan, The reflection coefficient of 25 ohms is 0.333 180, so if you do trim
the line stretcher for 180 degrees, then attaching the antenna will
determine how close you are to nominal R + j0. You need to reset your line
stretcher at each frequency until you obtain a 180 degree phase shift on the
return loss from the antenna. It is reasonable to assume that your antenna
has an impedance in the region of 37 ohms, so the 180 phase shift is
probably correct. For the reflection coefficient at 0.333 0 the input
impedance is 100 ohms. For such an antenna it is probably easer to just
tune the antenna for minimum reflection coefficient and forget the phase
angle.

Frank