Here are some measurements of 3 filters off the low pass filter board I designed and built. First harmonic of each band is at least -50db down. The 4th band which in my case was for 15m, was well out and I need to look at it to work out why, cap values is going to be my initial guess LOL. I built this thing and have never used it LOL. Though I got some new boards coming from JLCpcb this week and i hope to have a transmitter happening that I will use in combination with the HackRF One as a receiver.