I have a FlightAware Pro Stick Plus connected to the flightaware antenna in my loft. I was using a 5m cable to connect it to my pi. After seeing some comments about having as shorter cable as possible I got an adapter so I could plug the FlightAware Pro Stick Plus directly to the antenna without any cable in the loft. My coverages has gone from 200NM to under 100NM!
Should it have improved my range, is it possible I have a bad connector or is what I have done a bad idea?
That depends on what system you are using.
If you are using the flightaware system you can edit with SSH or remove your SD card and edit the file /etc/default/dump1090-fa
Probably you have the gain at -10, and that could be to much.
I have purchased the filter and fitted it. The order is FA Antenna, sma converter, filter, FA dongle, Pi Zero with no cable. Prior to this I had put the 5 Meter coax cable back.
You can see when I installed the filter and removed the coax. I wanted to remove the cable to increase the range, but it seem something is not right.