Maybe I did not understand it correctly, but it appears to me that you are using cables with open ends to connect to the transformers. If this is the situation, how do you calibrate the nanoVNA?.
if you have calibrated it with the SOL directly at the instrument ports, you are measuring the combined response of the transformer plus the cables and it lead to errors. If this is the situation, I would solder female SMA connectors to the transformer leads, calibrate the instrument using the test cables, and then connect these cables to the input and output of the transformers. Doing that you insure that the cables are included in the calibration and your measurements are done at the transformer connectors.
Regards,
Ignacio, EB4APL
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El 19/03/2020 a las 15:36, Kerr Smith escribi¨®:
Thank you very much for your suggestions - I really appreciate them and have learnt a lot from reading about the various ideas people have offered and from doing my experiments.
I have just re-done the CH0 to CH1 return loss test using a different set of cables and have got better results, the image is attached. Using these cables the return loss is -53dB at 1MHz and -33dB at 30MHz so pretty close to those shown by Roger and Arie.
I need to use my other cables though for testing as these have non-sma ends on that allow me to attach to the transformers. By non-sma ends I mean short wires but I assume (hopefully correctly) that at low frequencies (7Mhz) this should not make too much difference.
My next step is to attach my new transformers to the NE602 and see how the output looks.
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