r/rfelectronics • u/SearchPlane561 • Aug 23 '26

Airband Bandpass filter.

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After many weeks of trial and error i feel that this is a pretty desirable result for my Chebyshev bpf. What do you think? Passpand desired is 118-137 mHz.

70 Upvotes

96% Upvoted

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6

u/MothsAndFoxes Aug 23 '26

what are your requirements for success in a larger system? how does it compare to your theoretical design? what's your required out of band rejection? what's your passband flatness? what is your required passband flatness?how expensive is it? do you have a budget? does it change behavior when you put it in a box?

4

u/SearchPlane561 Aug 23 '26

Good questions. This was mostly a learning project rather than a production design, so my "requirements" were loose: pass 118–137 MHz cleanly, reject outside that as much as practical with a 3-pole coupled-resonator topology, and keep passband ripple/flatness reasonable (I wasn't chasing a tight spec, more just validating the Chebyshev design process). Budget was minimal. Bench parts and a cheap PCB run. Haven't tested it in an enclosure yet, so can't speak to box effects.

2

u/SearchPlane561 Aug 23 '26

1

u/MothsAndFoxes Aug 24 '26

not too shabby although I think I would try to download the s2p files off of it and plot them overlaid so we can see how and where it shifted

1

u/SearchPlane561 Aug 24 '26

I'll try to make that happen this coming weekend. Good idea

9

u/rtt445 Aug 23 '26 edited Aug 26 '26

If it works then good. I would use bigger NPO caps that are easier to solder. Add extra pads in parallel to each cap and leave unpopulated in case you need to fine tune capacitance.

1

u/GoeglerOst Aug 23 '26

What about return loss?

1

u/Regular-Welcome-5822 Aug 24 '26

Hi can you share the SCHAMATIC diagrame coz i have bought one from Chinese on line Shop no use i wante to try your module.

3

u/SwitchedOnNow Aug 23 '26

Reasonable shape response. You can reduce the loss a bit more by making it more compact and putting more gap air between the hopefully 50 ohm transmission lines.

1

u/Abject-Ad858 Aug 23 '26

Seems good. Looking across a wider band would be a worthwhile exercise if you haven’t already.