I now have an HP 8405A Vector Voltmeter. I also have a Narda dual
directional coupler. Here is how I plan to set up and measure things at
about 440 MHz (antennas, etc) so I can determine their impedance (view in
fixed-width font):


50 Ohm Coax 50 Ohm Coax
.----------. .-----------. .--.
| | | | | |
| | \ | Dual | \ | |
| RF Gen |------------|T Coupler L|-------------| | Load
| | / | | / | |
| | | R F | | |
'----------' '-----------' '--'
| |
.----------. | | .---------.
| |--| |--| |
'----------' | | '---------'
50 Ohms | | 50 Ohms
| |
\|/ \|/
.----------------------------------.
| B A |
| |
| |
| |
| HP 8405A Vector Voltmeter |
'----------------------------------'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


T is the transmitter port, L is the load port, F is the -30 dB forward
coupled port, and R is the -30 dB reverse coupled port.

The HP voltmeter is able to zero out the phase angle between channels A and
B. So, I'll put a 50 Ohm dummy load out there for the Load and set the phase
angle offset to zero.

Then I'll put the actual load out there for the Load and read the channel A
voltage, the channel B voltage, and the phase angle between them.

Then I'll calculate the impedance with:

Z = 50(1+Er/Ef)/(1-Er/Ef)

where Ef is the forward voltage and Er is the reflected voltage.

For my tests, I will assume the coax really is 50 Ohms and non-reactive.
Since A is the reference, it will appear to be a real number. Ef will be a
complex number.

I'm not looking extreme accuracy. About plus or minus 10 to 15 percent will
be acceptable. Will this work? Your thoughts and advice will be appreciated.

Thanks,
John