Hi GM7,
You write "I attach the test ficture (see photo) and then calibrate"? but what I see in the photo is not a testfixture but the Lowpaasfilter itself.??? You have to do a 2 port calibration just with the testcables and the calibration devices,? so the short open and load connected to the CH0 cable, and isolation with the load connected to the CH1 cable . The through you calibrate with the CH0 and? CH1 cables interconnected by the female to female adapter. After that you can connect the lowpassfilter and measure it.
Success
Jos
Op 4-6-2020 om 19:17 schreef GM7:The isolation you calibrate with the load connected to th CH1 cable
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Hi All,
I'm trying to test a set of Low Pass Filters for 40m, 30m, 20m & 10m. I'm getting consistent results for each of them but not the results I expected. I'm struggling to establish whether the problem is with the filters or with my test setup / calibration or even with the NanoVNA.
I've repeated this with and without a test fixture and got essentially the same results. I attach the test fixture (see photo) and then calibrate (reset, followed by open, short, isolation, thru). I then check the smith chart with short, open and 50ohm loads to sanity check the calibration.
The attached image shows the 30m LPF. It doesn't have the passband I would expect or the roll-off I would expect. Instead it's almost a linear roll-off over the range under test.
Can anyone help? For example by either correcting my test methodology or offering any advice. Thanks in advance.
