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Looks to me as if the filter is perfect. Well done and may all your filters work exactly as designed!
On Jul 7, 2020, at 09:02, Bob Benedict, KD8CGH <rkayakr@...> wrote:
I built a 20 m BPF. Since I have many to make, I made a holder with SMA connectors and decided to use my recently acquired NanoVNA for the first time with a filter. Filter analysis shows a center at 14.09 MHz and a 3 db BW of 1.39 MHz, which seems fine. Neither variable cap is at its extreme.
My concern is that the loss looks too low. I'm seeing 0.4 dB S21 loss. The VSWR is also 2. After calibration check with straight through wires scan reads VSWR 1.03, return loss -35 dB and S21 gain -.077 dB.