I want to share the same antenna for VHF (TX/RX 144-148 MHz) and for Airband RX-only (116-136 MHz).

I live on a very congested area where filter is a must, so I'm looking for the best solution for my needs:

  • Wide bandwidth (~30 MHz)
  • Transmit capable (> 20W power handle with low return loss/SWR)

Currently I use a DIY helical filter for TX and a low-power LC filter for airband, but switching them everytime is very combersome. I like the high "Q" of the helical filter, but its bandwidth is very limited (~5 MHz) and I believe they cant be streteched to cover such bandwidth.

My primary source of interference are strong FM stations in the neighborhood, so I need a high Q, sharp filter with a good degree of attenuation between 108 and 116 MHz.

Any advice in the best filter design? My simulations shows a LC band-pass filter (Butterworth/Chebyshev) would meet my "sharpness" requirements, but they tend to have high return loss (SWR) as well, which could compromise my TX requiriments.

I have some soldering skills and a NanoVNA, tuning the helical filter wasn't a big deal.

  • $\begingroup$ Hm, how do you do your RX/TX switching? technically, your bandstop filter doesn't have to part of your TX signal chain. $\endgroup$ – Marcus Müller Jan 13 at 17:32
  • $\begingroup$ The band-stop filter uses low voltage SMD components, it'll burn if I use it for transmission. $\endgroup$ – Aldoir Jan 13 at 17:44
  • $\begingroup$ exactly, so keep it out of your TX chain! $\endgroup$ – Marcus Müller Jan 13 at 17:45
  • $\begingroup$ The point is: My helical filter is great for TX/RX on 140-150Mhz, but it deeply attenuate Airband, so I have to switch to this bandstop to listen to airband. A wideband helical filter would solve my question, but it's not possible I believe. $\endgroup$ – Aldoir Jan 13 at 17:48
  • 1
    $\begingroup$ Not something I'm proud of, but it works :) imgur.com/a/0YKwsqN $\endgroup$ – Aldoir Jan 13 at 19:06

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