AT-11 Datasheet, PDF (2/15 Pages) List of Unclassifed Manufacturers – AT-11 Automatic Antenna Tuner

Introduction: The AT-11 is a full featured auto or semi automatic antenna tuner designed for HF (1.8 to 30
MHz) transceivers using 2 to 100 watts. The tuner uses a switched "L" configuration with 256 capacitor, 256
inductor and Hi/Lo-Z settings to provide over a quarter-million tuning combinations (figure 1)(figures
appear at the end of text). The "L" network works great with just about any coax fed antenna (dipole, vertical,
beam, ect). Tuning time is between 0.1 and 6.2 seconds.
Operation of the tuner is auto or semi automatic. In auto mode, the tuner will seek a 1.5 match anytime
the SWR is above 3.0. In semi mode, the tuner will seek a match when the tune push button is pressed. Both
modes require that more than 2 watts of RF power be present. Up and down buttons are used for fine tuning the
inductors and capacitors and can be used in either mode.
Three LEDs provide an indication of SWR. Green indicates SWR of less than 1.5, Green/Yellow is 1.5-
2.0, Yellow is 2.0-2.5, Yellow/Red is 2.5-3.0 and Red indicates more than 3.0. The fourth LED is a tuning
indicator. It is lit when the tuner is trying to find a match.
The AT-11 is a small to medium sized project. It should take the average builder an evening or two to
complete (we averaged 6 hours on the prototypes). Besides the normal building tools needed (soldering iron or
soldering pencil, wire cutters, screw drivers, ect), the only test equipment needed is an HF transceiver,
dummy load (or resonant antenna) and voltmeter.
Before starting, you may want to get a copy of the January 1996 QST article where the AT-11 first
appeared. Although not needed for construction of the kit, it contains a little more theory about the AT-11 along
with some pictures. If you don't have or can't find the article, a reprint may be available from QST, 225 Main
St., Newington CT 06111.
Hardware Changes: A few changes were made since the article. Please use the instructions, schematics and
figures included in this manual for building your kit. D20 was added to prevent damage from accidental
reversing of the power and ground supply. More bypass capacitors were added to help prevent stray RF on the
board. J3 was changed from a 10 pin to a 14 pin header. A coaxial power jack was added near the back of the PC
board. Some of the tuning capacitors were upgraded to 1000 volt types to reduce drift due to component heating
on the lower bands (80 and 160). The 4.433 MHz crystal was changed to a 8.0 MHz oscillator module.
Also notice that due to upgrades, the silk screen on the PC board may be incorrect for some components.
Use the parts placement sheet at the end of this manual for correct parts placement.
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