1

Hello i'm in process of creating band pass filters for my ham radio. I calculated the filter for 80m band basing on this website: enter image description here

And recreated it in reality: enter image description here

Then I started measuring it with nanoVNA, and tuning the trimmers to get best frequency response: enter image description here enter image description here enter image description here

As You can see, the frequency response is nearly as simulated, but I'm not sure about the impedance matching. Is this how the Smith chart should look like? Is this filter good or bad? I'm concerned about that, because the rosponse is not 50ohm in whole passband, but only on the sides of it. Also, is this How logmag of s11 should look like?

fifi_22
  • 111
  • 1
  • 1
    looks like C3 is a *little bit* too large, over-coupling the two resonators. If you were to decrease C3 value, bandwidth will decrease a bit, but should result in a better match at pass band centre. – glen_geek Nov 10 '22 at 19:55
  • Nice work! At first glance the S11 looks good (below -10, mostly -15 dB in the passband. Narrow the frequency scale and enlarge the vertical scale a bit so you can see the passband edges more clearly. As shown you can't easily see the frequency of the -3 dB or -10 dB points. (calibrate and save two configurations so you can flip between them - wide for tuning the stop band, narrow for the passband. markers at the desired edges). – tomnexus Nov 10 '22 at 21:29

0 Answers0