Re: BPF too good? #filter


Toroids are self shielding, as almost all the magnetic flux is enclosed in the toroid.  There may be some capacitive linkage to the nearby metal, but it would be very minimal.


On Tue, Jul 7, 2020 at 4:48 PM Jim Painter via <> wrote:
It looks like your test jig has two large metal brackets which are very close to the coils. Could they be screwing with the inductance? 


On Tue, Jul 7, 2020 at 9:02 AM, 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.


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