portable Vector Network Analyzer

The calibration window


In the calibration window you can create the required calibrations for reflection and transmission measurements:

flexible

You will have to set the parameters for calibration:

flexible

"From" and "To" defines the frequency span of the calibration. This should be at least the range you are planning to use for your measurements. They don't need to be exactly the range as the software automatically selects the right range later at measurement.

"Steps": The more steps you scan the longer the measurement will take. Ideally you use the same steps as later in the measurement but you can easily use less steps in calibration as the software will use interpolation for recalibration. It is recommended to use a number of steps which results in a scan using easy frequencies: E.g. If you scan from 800 MHz to 1 GHz in 201 steps, step size will be exactly 1 MHz (800 MHZ, 801 MHz, 802 MHz… 999 MHz, 1 GHz) whereas if you use 200 steps, the frequency step is 1,005 MHz and the measured frequencies will be 800MHz, 801.005 MHz, 802.010 MHz and so on. With the softwares interpolation both steps would be possible but it is easier to select frequency ranges that do not require interpolation at all.

"Averaging": This is the number for overscans that will be performed to reduce background noise. VNA will scan this numbers and the average of the scans will be used as calibration. Generally you should set this to 10 do decrease measurement noise. Using higher numbers will significantly increase measurement times.

"ADC AVG" this is the number of measurements per step that are performed and averaged. The minimum value recommended for this is 10. It can be increase especially when measuring antennas in noisy environment.

Linear/Logarithmic: Chose if you want to scan the frequencies on a logarithmic or linear scale.

Recommendation for calibration parameters:
-
General purpose scan: From 400kHz to 4200 MHz in 1001 steps, set both Averaging and Adc AVG to 10
-
High resolution scan: Chose the frequency range and steps exactly as you would like to scan it later in your measurement. Try to limit the number if steps to a couple of 100s (e.g. 201) and set both "Averaging" and Adc AVG to 10.

PocketVNA software has internal temperature compensation but results are best if device is warmed up. This is true especially for frequencies >2.7 GHz. For higher frequencies leave the device connected to the USB port for at least 20 minutes before calibrating.

Then you need to decide whether you want to make a reflection (S11) or transmission (S21) measurement:

Reflection
For reflection calibration you need a OSL calibration kit, consisting of an open (O), Short (S) and a (Load) standard.

Make sure "Reflection" is selected:
flexible

Now connect the open standard and click the scan button:
flexible

When the progress bar has reached 100% click on "use as Open":
flexible

To reduce noise of the measurement curve, the optional "Smooth factor" might be increased to a number higher than 0. This will make your measurement smoother. Be careful not to exaggerate on this or you will create a wrong calibration.

Proceed the same way for Short and Load standard.
Now your calibration window should look like this:

flexible


Now click "Save Calibration" and "Use and Close".

You should check if your calibration was successful for example by plotting measurements of open, short and load standards on a Smith chart:

flexible

Load should be in the middle of the digram, short at the very left and open at the very right end of the diagram. The measurements are no perfect dots, as the calibration standards are not perfectly reflecting (open, short) or absorbing (load).

Proceed to the
"live measurements" window to start your first measurement.

Transmission
For Transmission you only need to be able to connect port 1 and port 2. An open calibration standard is helpful but not required.

Make sure "Transmission" is selected:

flexible

Now, leave port2 open or connect the "open" standard to it and press "Scan".
When measurement is completed press "Use as Open".

Now connect port 1 and port 2 and press scan. When progress bar has reached 100%, press "Use as Through"

You should see something like this now:

flexible

Now click "Save Calibration" and "Use and Close".
Proceed to the
"live measurements" window to start your first measurement.