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.