So last week I added the FA filter and it seems that my metrics have dropped over the last week compared to without it. On average of approx 150 AC less a day compared to last week. I was expecting to get more with the bandpass added. Thoughts? Am I doing something wrong?
Do you have strong interfering signals nearby? That is the situation that adding a filter is meant to address - the case where the receiver is being deafened by non ADS-B signals (usually a nearby cell tower). If you don’t have strong signals nearby, then adding a filter won’t do anything for you and in fact will add some signal loss.
You might check to if you have a bad connection. I installed filters on 2 Pi’s and one of them had significantly fewer a/c after installation. The problem was a bad pin on one SMC connector.