Autek Research IC Active Audio Filter QF-1 for CW/SSB/AM, TESTED

Description: This is a used vintage (circa 1977) audio filter based on analog filtering techniques, using DIP op amps and discrete components, so if repair were ever needed, you could do it. It provides one filter with adjustable peak, notch, or lowpass filter characteristics, switch selectable. The peak function can have bandwidths as narrow as 40-50Hz. All three filter characteristics have been tested (listening to FT-8) and they work great. However, there is some 60Hz (or 120Hz) hum present. The filter is useable as is, but you might want to renew the power supply capacitor(s) to eliminate the hum for better listening pleasure. This unit connects between the output of a radio receiver and a speaker (or headphones) using a quarter-inch mono phone plug and jack. A typical use is say you are a ham (amateur radio operator) listening to CW (Morse code) on a receiver that has a wide passband resulting in hearing several CW conversations (QSOs) at different pitches simultaneously, so you engage the peak filter and adjust the frequency to match the pitch you are interested in, thereby greatly attenuating the other signals and amplifying the desired signal. The lowpass filter can help make SSB (single side band) audio more intelligible, and the notch filter can tune out an annoying CW signal or birdie that is interfering with your SSB signal. This unit has been modified to include a bypass switch so that you don't have to remove the device in order to pass through the audio signal without modification. This device is an old-school solution. Vintage ham radios didn't have much selectivity, not nearly as much as modern radios, so this audio filter improved listening pleasure. The manual, which has schematics, is available online. See attached photos thereof. Thanks for looking.

Price: 33 USD

Location: Santa Rosa, California

End Time: 2024-11-28T01:35:22.000Z

Shipping Cost: 0 USD