I have found that a Fox Tango Corp. 89H2.1 IF filter has previously been installed in a used FT-101ZD Mk 0 that I purchased. ?I have no documentation for this installation, and cannot find any?on the internet.? The original Yaesu SSB filter was left mounted on the PB-1963B UNIT (IF board) and the Fox Tango filter mechanically attached to the Yaesu filter case with copper foil tape.? A small PCB; with what looks like a transistor, a resistor, fixed capacitors, a variable capacitor, and inductor; is mounted with double sided tape atop the Fox Tango filter; I assume this is for impedance matching and possibly an amplifier. ?A small gauge red/white wire has been run from underneath the PCB through a mounting hole for the presently empty CW filter space, to the small PCB. ?(I expect that?this wire will need to be rerouted to properly install a CW filter.) ?Coaxial “jumpers” were connected from the Fox Tango filter I/O to test pins atop the IF board. ?

Do you have any information concerning this Fox Tango filter installation-modification, so I can clarify the functionality (either impedance matching or amplifier, or both) of the small circuit atop the filter, and for reference when needed, to understand exactly what has been done? ?In general, I understand an SSB 2.1 KHz wide (@ -6 dB?) IF bandpass (crystal ?) filter has been installed, while I would like to understand why the original filter was left in the radio. ?Is the original SSB filter still functioning in the radio? ?Also, I would like to know insertion loss and all specifications of this 2.1 KHz IF filter. ?A filter response curve plot would be great, expecting that to accompany the written specifications.??The schematic, installation instructions, and filter specifications documentation would clarify, and answer my questions.

Does the variable bandwidth control still function as described in the Yaesu instruction manual, with exception to the maximum bandwidth? ?It is a mystery to me why the original filter was left in the radio, unless it is cascaded with the Fox Tango Corp. filter. ?Is the original SSB IF filter functional in the radio, or has it been electrically isolated and left mounted on the IF board? ?Does anyone have actual experience with using the Fox Tango 2.1 KHz IF filter in operation with the FT-101ZD

who could qualitatively comment on its effectiveness and performance?