Dave, in days gone by I purchased some filters to remove 2175 hz used in
tone remote keying in wireline remote control of base radios. The filter
removed the hold tone from the voice path. They were manufactured by Cetac
Vega company - seems like in Washington State and consisted of a torriod
coil and associated capacitors. You might also find a similar audio notch
filter in surplus station cards used in Motorola Micor / Motrac, etc
stations that had tone remote control. I hope this helps. Best 73, Steve
NU5D
