Antenna Tuners – Kessler Engineering, LLC, Ohio

AT-AUTO Auto Tuner

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The AT-AUTO is a fully autonomous, fully automatic impedance matching network (an antenna tuner) that employs an embedded microprocessor to position a conventional roller inductor and a split-stator variable capacitor. It provides continuous coverage tuning from 1.8 – 54 MHz (including MARS, DoD, and commercial frequency bands, etc.) and is rated for 1500 W continuous carrier operation. The AT-AUTO is quiet and reliable, and with its industrial-rated stepper motors, provides a superior impedance match to that provided by the loud clanking boxes of relays provided by the competitors.

The AT-AUTO continuously measures forward and reflected RF power. As long as the SWR is below a user-selectable threshold, the AT-AUTO provides a “Good Match” cue in the Liquid Crystal Display (LCD) and takes no further action. Whenever the SWR exceeds the “Tune-Start” SWR, the AT-AUTO then counts the RF carrier frequency, looks up previously stored Inductor (L) and Capacitor (C) settings for the frequency of operation and then repositions L & C to the recalled settings. If the SWR is still excessive, the AT-AUTO automatically begins tuning, and provides user prompts during the entire process via the LCD. Once a good match is found, the new match settings are stored in memory for subsequent recall. The default behavior is highly customizable to suit individual needs.

The AT-AUTO is also able to obtain frequency information via the radio’s serial data port (for these compatible radios so equipped). By doing so, the AT-AUTO instantly follows frequency changes (VFO adjustment, etc.) and immediately recalls and sets the L & C for the new frequency – without the need to generate an RF carrier! The recalled match should provide an excellent SWR so that when RF is finally applied, subsequent tuning will not be necessary. While the serial port is not necessary for automatic tuning, this “Smart Mode” of operation greatly speeds the entire process of changing frequencies.

The AT-AUTO is also capable of automatically selecting up to 8 coaxial outputs (via the companion CX-AUTO coaxial switch). Additionally, the AT-AUTO may also be shared with up to 8 different radios when utilizing a CX-AUTO on the “input-side” of the AT-AUTO. Please see the CX-AUTO link for additional information.

Note: The AT-AUTO is currently not in production and not available for sale. It is undergoing a redesign for release soon. The pictures and descriptions shown here are of the existing version(s) of the AT-AUTO tuner prior to its production cessation.

A new web page for the AT-AUTO II is coming in the near future.

Update Your Tuner’s Firmware

Kessler Engineering provides the latest versions of the tuner’s firmware available for download. Works on Windows PC’s only. Support for older firmware versions is available here, too. Download the bootloader Zip file below to install firmware.

Bootloader zip file