NanoVNA. High-precision calibration.

High-Precision SOLT (OSLT) Calibration

A Vector Network Analyzer (VNA) is a precision instrument whose readings directly depend on calibration. Without calibration, the VNA displays not the parameters of the measured antenna or filter, but the characteristics of the entire measurement line (including the parasitic capacitance and inductance of the connecting cables and connectors).

The OSLT Calibration Procedure

To perform the calibration, a set of calibration standards from the kit is used: OPEN (open connector, infinite impedance), SHORT (short-circuited connector, 0 Ohms), and LOAD (matched 50-ohm non-inductive load). It is vital to perform the calibration exactly at the end of the cable to which the Device Under Test (DUT) will be directly connected.

Crucial Interpolation Rule:

When changing the frequency range (START/STOP), the device automatically interpolates the calibration matrix, and the calibration status is displayed with a lowercase 'c0'. To ensure maximum accuracy at high frequencies (RF), it is highly recommended to recalibrate the device completely in the narrow target frequency range.

Step-by-Step Calibration Algorithm:

1. Preparation: Set the required frequency range via the STIMULUS menu (START/STOP). Go to the CAL → RESET menu to clear the current calibration matrix. Tap CALIBRATE.
2. OPEN Calibration: Attach the OPEN standard to the end of the CH0 measurement cable. Tap OPEN. Wait for the scan to finish and the menu item to become highlighted.
3. SHORT Calibration: Remove the OPEN standard, attach the SHORT standard. Tap SHORT. Wait for the item to highlight.
4. LOAD Calibration: Attach the LOAD (50 Ohms) standard to CH0. Tap LOAD. Port CH0 (Reflect S11) is now fully calibrated.
5. ISOLATION Calibration: Attach the LOAD standard to port CH1 (if a second load is available) or leave CH1 entirely open. Tap ISOLN.
6. THRU Calibration: Connect ports CH0 and CH1 directly with the measurement cable using an SMA female-to-female barrel adapter. Tap THRU. The device will compensate for the transmission frequency response.
7. Completion and Saving: Tap DONE. A memory slot selection menu will appear. Select SAVE 0. The SAVE 0 profile is the default profile and is loaded automatically every time the device is powered on.

Express Calibration Verification

After completing the calibration, keep the SMITH CH0 chart active and check your standards:

• When OPEN is connected: The point on the Smith chart must be located strictly on the far right edge of the horizontal axis.
• When SHORT is connected: The point must be located strictly on the far left edge of the horizontal axis.
• When LOAD is connected: The point must be located exactly in the geometric center of the Smith chart (50 Ohms).
• When ports are connected with a THRU cable: The S21 LOGMAG graph should display a perfectly horizontal line exactly at the 0.00 dB level.

Correct positions of OPEN, SHORT, and LOAD points on the Smith chart after successful calibration.

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