PocketVNA is a research tool for laboratory usage only. Keep away from humid or hazardous places. Always read the manual and safety instructions prior before using the pocketVNA.
This is a temperature sensitive measurement device! Expose to temperature or direct sunlight might affect measurement results!
With the pocketVNA you can measure a variety of electrical parameters in the range from below 1 MHz up to 4 GHz. In order to properly make use of this measurement device you should be comfortable with the following concepts:
- S Parameter
- Any other parameter you are interested in measuring (return/transmission loss, VSWR, complex impedance…)
In short: A frequency generator inside the pocketVNA creates a voltage oscillating at the given frequency. At the frequencies we are measuring, the created signal can be considered as an electromagnetic wave traveling along e.g. a cable connected to the pocketVNA port. When this signal is input to the device under test (DUT), the signal is altered in phase and amplitude.
In a 1-port configuration what is measured, is the wave that is reflected from the DUT back into the pocketVNA port. The measured scattering parameter (= S parameter) S11 is the ration between the incident and the reflected wave. The theoretical minimum of S11 is 0, that is when nothing of the signal is reflected. For passive devices it is maximum 1, when 100% of the incident wave is reflected. For active devices (e.g. an amplifier) S11 can be higher than 1.
In a 2-port configuration (DUT is connected to both port 1 and port 2) we also can measure S21, that is the ration between the voltage output from port 1 and the input in port 2.
Note, that both S21 and S11 are complex numbers. Real part of S-parameter represent the change in magnitude, imaginary part represent a phase shift.
Gain or loss can be calculated by converting the S parameter into decibels:
g=20* log10(|S|); where S is either S11 or S21
From the S parameters, other measures such as the impedance Z or VSWR can be calculated:
Z = 50 * (1-S)/(1+S);
s = (1+|S|)/(1-||S|)
Generally, the magnitude and phase of the electromagnetic wave is not only altered by the DUT, but by connectors and cables and last but not least by the components inside the pocketVNA.
This is the main reason, why network analyzers need to be calibrated. There are many ways to calibrate a VNA, only OSL (open short loop) calibration will be described here as it is the one used with the pocketVNA. For OSL, three calibration standards are required:
- Open: Ideally this would imply infinit isolation between signal and ground. In practice, economic open standards are only termination caps shielding the signal from the surrounding
- Short: Ideally a short standard would short signal to ground with 0 impedance over the complete frequency range.
- Load: Ideally, load standard would connect signal to ground with the load impedance (50 ohms in our case) over the complete frequency range. This way the S parameter would be 0 and the return loss infinite.
When doing our calibrations we will find out that we are quite far away from the ideal case.
To install pocketVNA follow the installation guide and to start your first measurement please use the quick start guide.