Re: NanoVNA #calibration

Dave W6OQ

What I see in the plot that you posted is a filter that is about 170 kHz wide at the -3 dB points and centered at 10.715 MHz. This is consistent with a Murata SFELF10M7HA00-B0 that has a spec of 180 +/-40 kHz and a center frequency of 10.7 MHz +/-30 kHz. The fact that all the filters exhibit the same response wouldn't surprise me if you purchased them at the same time, they probably came from the same batch, and the tolerance is likely based on batch to batch differences caused by process variations rather than random variations within a batch.

It is a little harder to understand/explain the fact that the low frequency side runs out of dynamic range at -60 dB and the high side gets there at 5 dB higher at -55 dB. Since these filters are symmetrical, have you tried swapping the input and output by turning the filter around at the fixture?

Also, you haven't really detailed your circuit for matching the 50 ohm of the VNA to the 330 ohm of the filter. If I were doing it, I would use a minimum loss matching pad. This would consist of a 54.281014769949586 ohm resistor (it is the value that the calculator gave - LOL) across the input and output coax to the VNA and a series resistor of 304.01167774007837 ohms up to the filter input/output. This would give a loss of 13.867585162369918 dB on each side. 5% values: 56 and 300. 1% values: 54.9 and 301. I am sure the 5% values would be just fine. You could bridge the filter location with a short on your test fixture to determine the exact loss through the pads, then place the filter in the fixture and easily find the filter insertion loss.

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