I am looking for ideas to improve my Impedance measurements I perform on my VLF antenna system.
Due to circumstances my VLF experiments are usually "on location / in a field" so I do not have the luxury of a fully stacked workbench.
The setup I have is: - a function generator - 4000 Hz output - an audio amplifier - feedline - Antenna
I consider the feedline part of the antenna system, and I use the following method of determining the Impedance of the antenna system:
- Measure the open output voltage of the Amplifier = Vopen
- Measure the output voltage with a known load (Rload=1000) = Vload
- Calculate the output impedance of the amplifier Rout = Rload * ((Vopen/Vload)-1)
- Measure the output voltage with the antenna system = Vant
- Calculate the antenna system impedance Rant = Rout / ((Vopen - Vant)-1)
I would repeat this process with multiple values of Rload to ensure measurements are accurat; usually I use the following values: 1000 Ohm and 2400 Ohm.
This way I can determine/tune the antenna system to come as close to 8 ohm impedance which the amplifier wants to see.
My questions are:
1) is this method correct ?
2) are there better methods given the limitation of being "on location" ?