I have for sale an excellent working Timewave DSP-599zx audio filter. This is one of the best outboard DSP units and will work great with your older HF radios without the DSP features. The DSP-559zx is an extraordinarily versatile digital signal processor designed for amateur and shortwave radio voice, data and CW operation. The DSP-599zx uses advanced digital signal processing technology to implement algorithms that perform five basic audio functions: Random noise reduction Adaptive multi-tone and manual notch filtering (Tone noise reduction) Bandpass/Highpass/Lowpass filtering Signal generation including FSK RTTY modulation Signal detection and measurement including RTTY demodulation The DSP-599zx combines these five basic functions to reduce noise and interference and improve radio communication. The DSP-599zx hardware and software architecture allow easy field upgrade with new features and algorithms. The same hardware and software architecture also allow ergonomic mode oriented operation of the DSP-599zx. The LCD alphanumeric display provides a clear view of operating settings when switching between operating modes. The quick-select push buttons and optical encoders for filter tuning allow instant mode change with total recall of last setting and memories. Front-panel selectable and adjustable inputs allow you to quickly setup and adjust your DSP-599zx to wipe out noise and QRM like never before! Here are a few more highlights among the many other operating features of the DSP-599zx: Selectable Automatic Gain Control Configurable bypass control Two selectable input channels Two configurable output channels Six memories for instant recall of user-defined configurations Test instrument mode for analyzing signals and other equipment Check out the reviews for this unit at; http://www.eham.net/reviews/detail/209 More information on this unit can be found at; http://www.timewave.com/dsp599zx.html Price is $265 shipped CONUS.