I have a Ten-Tec model FR-4 audio filter here. It uses the sam case as
the KR-40 keyer. The front panel has an IN/OUT switch, phone jack and
min/max control. On the back is a short cord with a phone plug for
inserting into the speaker jack of your rig. This this is passive as it
requires no external power. Inside are several torriods and capacitors.
Has anyone else seen one of these or have any information? I don't have
any documentation and can't recall seeing them advertised. Any comments
will be appreciated.
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