PAR Electronics seems to have some great filters for scanner enthusiasts.http://www.parelectronics.com/scanner.htm
Their VHF-FM filter will probably benefit airband listeners. It notches the FM broadcast band (88-108 MHz), which is often a source of trouble for airband listeners who live close to high-power FM radio stations.
From their catalog:
"The VHF-FM filter is a classical 3 pole filter designed to substantially reduce signals from the FM broadcast band by a minimum of –25 dB and a maximum of –50dB. A 10 turn precision piston capacitor allows the end user to custom tune one of the notches ( it is factory preset at 98 MHz). Loss at 116 MHz is only –3dB, dropping rapidly from there to only -1.7 dB at 120 MHz."
Universal Radio carries this filter for $66.95 (Order #0098).
There is also the BCST-HPF for those experiencing interference from AM broadcast stations. It passes 1.8-200 MHz and notches out 0-1.7 MHz.http://www.parelectronics.com/swl_filters.htm
Universal Radio has it for $48.95. Order #4426
If you don't hear radio stations on your feed or on your scanner while listening to airband, you probably do not need one of these.