Exploiting your antenna analyser #16

Measure inductor using OSL calibration

At Measuring balun common mode impedance I showed a method of backing out the effects of a text fixture using the “subtract cable” facility of Antscope software with the Rigexpert AA-600.

Some analysers (including the AA-600) support OSL calibration of the instrument itself, and some support OSL calibration using the client software (Antscope in this case). This article demonstrates use of Antscope with OSL calibration to measure a small RF inductor which has similar characteristic to good Guanella 1:1 HF baluns.

The text fixture used for this demonstration is constructed on a SMA(F) PCB connector using some machined pin connector strip, and SMA(M)-SMA(M) and N(M)-SMA(F) adapters to connect to the AA-600.

Aa600Fix02

Above is a pic of the test inductor in the test fixture with adapters. The test inductor 6 turns of 0.5mm PVC insulated wire wound on a BN-43-202 binocular balun core.

Uncalibrated measurement

Screenshot - 05_05_16 , 07_11_06

Above is a measurement of the inductor in the test fixture. The reported values are not correct, because the DUT is some 70mm from the reference plane of the basic instrument. Backlevel Antscope is used here (v4.2.57) as newer versions to this date have been ‘improved’ and cannot display this graph. It is unfortunate that the |Z| trace cannot be turned off, poor software.

OSL calibration

Before measurement is made of the inductor, the test fixture must be calibrated with an OPEN, SHORT and LOAD.

Aa600Fix01

Above are the OPEN, SHORT and LOAD components, the load is two 100Ω 1% SMD resistors in parallel. The reference plane is a point about 1mm below the top of the pins, I one was obsessive, 1mm should be trimmed from the OPEN… but the effect will be very hard to measure at these frequencies.

The OSL calibration is performed using Antscope and the with OSL calibration activated, a measurement is made of the DUT. The implementation in Antscope is not very elegant, but it works.

OSL calibrated measurement

Screenshot - 05_05_16 , 07_07_39

Above is a measurement of the DUT with OSL calibration. It is immediately obvious that the reported values are quite different, the self resonant frequency is almost three times that reported by the uncalibrated test. (Again the obligatory |Z| trace and the common amateur graph defect, the blue trace following the top edge of the grid, poor software.)

Watch the blog for continuing postings in the series Exploiting your antenna analyser. See also Exploiting your antenna analyser – contents.