All,

The setup is an 8407a network analyzer with an 8412a display. The
forward and reflection detectors are mini circuits ZFDC 20 - 4's. These
are power detectors.

The question is: With a short stub on the detector will the open or the
short represent zero phase angel?

The setup basically is working. Open and short read 180 degrees apart. A
cap and an inductor are plus and 180 apart and 90 out of phase with the
open and short.

Thanks - Dan

dansawyeror wrote:
The question is: With a short stub on the detector will the open or the
short represent zero phase angel?

Assuming the phase angle is between the voltages:

The phase angle between Vfor and Vref at an open circuit
is zero (all the energy is in the E-field).

The phase angle between Vfor and Vref at a short circuit
is 180 degrees (all the energy is in the H-field).
--
73, Cecil http://www.w5dxp.com

Thanks.

The detectors are classified as power detectors. What effect would that
have?

If it would be the same then the open would be zero.

- Dan

Cecil Moore wrote:
dansawyeror wrote:
The question is: With a short stub on the detector will the open or
the short represent zero phase angel?

Assuming the phase angle is between the voltages:

The phase angle between Vfor and Vref at an open circuit
is zero (all the energy is in the E-field).

The phase angle between Vfor and Vref at a short circuit
is 180 degrees (all the energy is in the H-field).

dansawyeror wrote:
The detectors are classified as power detectors. What effect would that
have?

Power is a scalar and doesn't have a phase. If phase
is required in a power equation, it is normally the
phase between the associated voltages, e.g. the phase
used in the interference term in the irradiance equation
in optics is the phase between the (visible) E-fields.
I would assume the power detector phase convention would
be the same as in optics, but I'm not absolutely sure.
--
73, Cecil http://www.w5dxp.com

Cecil,

Thanks for the pointer. I split the sweep signal input and fed the
analyzer with 'in phase' signals. I then set the analyzer phase to a
known reading, line on the phase display. I then tested this by
comparing it to short and open. It was almost identical to the short
reading, less then about 4% difference.

This is being used to analyze a loaded dipole without any input network.
With above setup the antenna is now reading 'inductive' which is
consistent for this network.

The next step is to determine the amount of capacitance to bring the
reflection to 0j at the frequency of interest. This could result in a
reading of 0 or +/-180 degrees phase. If it is 0 then the impedance is
less then 50 Ohms, if it is 180 then the impedance is greater the 50 Ohms.

Thanks - Dan

Cecil Moore wrote:
dansawyeror wrote:
The detectors are classified as power detectors. What effect would
that have?

Power is a scalar and doesn't have a phase. If phase
is required in a power equation, it is normally the
phase between the associated voltages, e.g. the phase
used in the interference term in the irradiance equation
in optics is the phase between the (visible) E-fields.
I would assume the power detector phase convention would
be the same as in optics, but I'm not absolutely sure.

On Mon, 19 Mar 2007 16:08:17 -0700, dansawyeror wrote:

Cecil,

Thanks for the pointer. I split the sweep signal input and fed the
analyzer with 'in phase' signals. I then set the analyzer phase to a
known reading, line on the phase display. I then tested this by
comparing it to short and open. It was almost identical to the short
reading, less then about 4% difference.

This is being used to analyze a loaded dipole without any input network.
With above setup the antenna is now reading 'inductive' which is
consistent for this network.

The next step is to determine the amount of capacitance to bring the
reflection to 0j at the frequency of interest. This could result in a
reading of 0 or +/-180 degrees phase. If it is 0 then the impedance is
less then 50 Ohms, if it is 180 then the impedance is greater the 50 Ohms.

Thanks - Dan

Dan, a short represents zero impedance, thus if resistance is less than Zo with zero reactance, the phase of
the reflection coefficient is 180°. Conversely, an open represents an infinite impedance, thus if the
resistance is greater than Zo, the reflection coefficient is 0°.

Walt, W2DU

Walter Maxwell wrote:
"Dan, a short represents zero impedance, thus if resistance is less than
Zo with zero reactance, the phase of the reflection coefficient is 180
degrees. Conversely, an open represents an infinite impedance thus if
the impedance is greater than Zo, the reflection coefficient is zero
degrees,"

Succinctly and well stated.

Graphics of the voltage vectors (phasors) along open-circuited and
high-impedance terminated transmission lines are gicen by Terman on page
91 of his 1955 opus. At the high-resistance termination point, it is
seen that the incindent and reflected voltages are in-phase and thus
add.

I seem to recall that this results in voltage doubling at the open
circuit due to interruption of current at the open circuit which forces
the magnetic field energy to be temporarily transferred to the electric
field (Cecil`s conservation of energy at work). Again relying on a very
old memory, I believe we called this voltage doubling the "Ferranti
effect".

Best regards, Richard Harrison, KB5WZI

Again relying on a very
old memory, I believe we called this voltage doubling the "Ferranti
effect".

Best regards, Richard Harrison, KB5WZI

Jeez, I always read it as the 'Ferrari effect", where having a red
Ferrari doubles your electric pull on young, nubile, females... Guess
my dyslexia let me down...

denny / k8do

Richard Harrison wrote:
Walter Maxwell wrote:
"Dan, a short represents zero impedance, thus if resistance is less than
Zo with zero reactance, the phase of the reflection coefficient is 180
degrees. Conversely, an open represents an infinite impedance thus if
the impedance is greater than Zo, the reflection coefficient is zero
degrees,"

Succinctly and well stated.

Graphics of the voltage vectors (phasors) along open-circuited and
high-impedance terminated transmission lines are gicen by Terman on page
91 of his 1955 opus. At the high-resistance termination point, it is
seen that the incindent and reflected voltages are in-phase and thus
add.

My 15th edition of The ARRL Antenna Book has those
phasor diagrams, Fig 8 and Fig 9, on page 24-5. Since
Walter Maxwell was a contributor, I'll bet that those
are Walt's phasor diagrams.
--
73, Cecil http://www.w5dxp.com

Cecil, W5DXP wrote:
"Since Walter Maxwell was a contributor, I`ll bet that those are Walt`s
phasor diagrams."

My 19th edition of the ARRL Antenna Book has the same diagrams in
Chapter 24. The phasors look right so they well may be Walt`s.

Best regards, Richard Harrison, KB5WZI