New life for old filter - 2M LPF

Filter sweep 50-500MHz

Early last year I built some filters for a project I was involved in, today I dug out one that was labeled 350MHz LPF because I need a filter to go after the 250mW amplifier on the HackRF. I swept the filter and noted that it had a fair dip well before 350MHz so the label didn't really seem to fit. A little bit of trimming by spreading the turns of the inductors and tweaking the variable capacitor and I seem to have something good enough for 2M. Insertion loss looks to be about 0.5dB on 2M, down 19dB on the first harmonic and 48dB on the 3rd. That should be plenty to keep the HackRf / MGA31189 amp combo clean.

2M LPF

One thing about the sweep, this is on my rather old 23GHz spectrum analyser and 18GHz sweep generator, the two are not sync'd so I have set the sweep time on the generator to 60 seconds and left the analyser free running. The result is okay but nothing like using the modern Rigol DSA815 or the HP's I have access to... oh well.