This article documents an InsertionVSWR test of another cheap Chinese 1-9 balun purchased for less than <$5 on eBay (shipped).
Above is the advertising pic of the 1-9 balun, it would seem to be a clone of the Noelec 1-9 balun. The balun is a compensated voltage balun with the secondary centre tap grounded for these measurements.
The measurements were made with a NanoVNA-H4 v4.3 running DiSlord v1.1.0 firmware.
The 200 ohm load is a 1% 1210 chip resistor soldered to header pins.
The primary and secondary inductance was measured at 1kHz with an LCR meter, for 15 and 65µH respectively… hinting that it is a 1:4 transformer.
On that basis it was measured with a good 200Ω load.
Above is the NanoVNA screenshot with e-delay set to make the compensation capacitor location the approximate reference plane. ReturnLoss>20dB (ie |1/s11|dB) above 3.6MHz, and no hint that it is grossly overcompensated as in some that have been tested.
Above is a screenshot of NanoVNA-APP showing the VSWR plot.
Above is a plot of R,X at the reference plane (the compensation cap on the PCB).
As far as the scan goes (1-30MHz), the transformer is clearly 1:4 impedance ratio, and has quite good InsertionVSWR above 3.6Mhz.
This is clearly not the 1:9 ratio that it was sold as and labelled as, Chinese Quality… bit of an oxymoron really!
The module could be used as a test fixture, OSL calibrated with loads on the DUT terminals, and the correction process of the VNA papers over the less than ideal transformer behavior to a large extent.