This is a sample Jupyter Notebook Cell to use as a starting point for Transmission Line Experiments It is used with Touchstone format S-Parameter data files acquired from VNA measurements and selected immediately below. Generally two test fixtures are attached at end of test cables where serve to adapt to the environment of a device or line under test.

SOLT and TRL calibrations can be performed to provide input to this notebook for analysis.

Example files involve using 1m, 2m and 4m Line standards, 100 ohm resistor Load standard, Open and Short standards.

Lines can be prepared by cutting 146" of inexpensive CAT5 UTP cable and using an electric drill to separate the pairs while being careful not to change the twist of each pair. Leave one pair at full length for the (electrical) 5m test cable. Cut another pair to 58.4" to use as the 2m test cable and the a remaining pair to 29.2" to use as the 1m test cable.

Using as low soldering iron temperature as possible to avoid damaging any thin copper plating, first tin and then solder PCB mount SMA connectors to each end of each cable. Connect the solid color conductor to the center pin of the SMA connector.

For this example, the VNA is set to sweep from a frequency where the longest 5m line is about 20 degrees long up to an upper frequency where the shortest 1m cable is about 150 degrees long. A large number of points are used to cover various analysis scenarious. In this example a nanoVNA-v2-plus4 is used with nanoVNA-qt andwith a NULL calibration file which sets the frequency range from 3 MHz to 125 MHz.

A test fixture using mix -41 binocular core BN-43-7051 with a 2 turn primary and 3 turn secondary makes a reasonable choice over the HF frequency range while 512 points produces a 239 kHz step size so the resulting NULL calibration/setup file has a header of

'512 3000000.000000 239000.000000 50 50' and sets up a sweep for 3MHz to 125.129 MHz

From nanoVNA-qt load TRL-1m-2m-5m-512pointNull.cal

This sets up the nanoVNA to calibrates with SOLT. Also save each measured calibration standards for use with TRL calibration. At Port1 measure calibration standards:

• SOLT-1m-2m-5m-512point-open.s1p

• SOLT-1m-2m-5m-512point-short.s1p

• SOLT-1m-2m-5m-512point-110ohmload.s1p

The 1m, 2m and 5m CAT5 UTP lines can then first be measured with their Port2 end left disconnected rather than connected to its test fixture to give

• SOLT-1m-UTPCAT5-open.s1p

• SOLT-2m-UTPCAT5-open.s1p

• SOLT-5m-UTPCAT5-open.s1p

and again, but connected to Port2, to measure the them as 2-port devices. Save the results.

• SOLT-1m-UTPCAT5-thru.s2p

• SOLT-2m-UTPCAT5-thru.s2p

• SOLT-5m-UTPCAT5-thru.s2p

After this SOLT calibration and measurements the TRLcalibration program in the second cell can be used to estimate the impedance of each of the three lines and also generate S-parameter files for them.When the cell is run a TRL Calibration Tool application window will pop up. After selecting and using the SOLT-measured standards from above TRL-corrected LUT files can be selected as DUTs, one-at-a-time, plotted amd their data saved as

• TRL-1m-UTPCAT5.s2p

• TRL-2m-UTPCAT5.s2p

• TRL-5m-UTPCAT5.s2p

so that the two different calibration and measurement techniques can be compared.

Line Impedance estimate using the SOLT measured data.

The SOLT xxx-open.s1p measurements can be used to estimate line impedance by measuring the series reactance at one half the frequency where the line's length becomes a quarter wavelength and rotates the measured value to a short. Note this frequency and measure the impedance at half of that frequency. At this length where the line is one-eight wavelength long that impedance becomes an estimate of the line's impedance which can be compared with the TRLcalibration utility result.