LDG AT-11 User guide

AT-11 Automatic Antenna Tuner

LDG

ELECTRONICS

Assembly Manual

Ver 2.4a

LDG Electronics

1445 Parran Road St. Leonard MD 20685

Phone: [phone] Fax: [phone]

e-mail: [e-mail] http://www.radix.net/~ldg

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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Software Changes: Several months after the AT-11 was released, some users noticed spurious noise
emitting from the chip. These "birdies" could be heard on a receiver at various places across the HF spectrum.
The software was changed to allow the AT-11 to go into sleep mode and extinguish the birdies.

The new software changes some of the operating features. At power on and in Semi mode, if there is no
RF, there is no noticeable difference. If there is RF, the tuner will tune to find a match. Once finished with
tuning and RF is removed, the processor will shut down, go into sleep mode and the birdies are gone.

In the sleep mode, the LEDs are disabled. You will not get the SWR indication when RF is present. The
Cap and Ind Up/Down buttons are also disabled while in sleep mode. Pressing the Tune switch with no RF
applied will wake up the processor (the LEDs will flash once). The LEDs will then indicate SWR when RF is
present and the Up / Down buttons will also function.

If you are in the Auto mode, the processor will not go to sleep because it has to monitor the SWR for 3.0
or higher to make another tune. Pressing both Down switches at the same time forces the processor into sleep
from either, semi or automatic mode.

Building the Kit: Before getting the soldering iron out, go through all of the parts in the kit and
familiarize yourself with each component and its placement. Most of the parts are common, but a few of them
may be new to some builders. There are just over 200 parts and 500 solder connections, so take your time.

Once familiar with the parts, start with the eight T-106 toroids (they are red and just over an inch in
diameter). Take care to not drop them, they will break. Use the number #18 gauge wire provided to wind L1-

8. For consistency, we count one turn when the wire passes through the center of the toroid. L1 and L2 just
loop at the bottom of the toroid (figure 2). L3-L8 are evenly spaced around (figure 3). Use the inductor table
to cut the wire to length (figure 4). Wind each toroid in the same direction as shown. Trim the wire to about
1/2 inch and scrape away the insulation from the end. Don't solder them in until later.

Next, wind T1 with 10 turns (figure 5). It is the small, black toroid and just under 1/2 inch in
diameter. The windings use the smaller #28 gauge wire and are made bifiliar. This means to use two lengths of
wire and wind them at the same time. It doesn’t matter if you twist them or wind them side by side. Connecting
Green 1 and Red 2 together forms the center tap of T1. Be sure to note that the wire on the left side come from
under T1 and the wires on the right side come over the top side of T1. Trim the wire to about 1/2 inch and
scrape away the insulation from the end. Do not install T1 until later.

Note that some of the silk screen may have been drilled away when it was fabricated. Use the parts
placement layout in the back of this manual to assist in locating where parts are installed.

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Parts are installed and soldered in order of height, from shortest to tallest. With the PC board blank, it
is easiest to install all of the resistors first. Be sure to check the values with the parts list. Most of the
resistors are 1/8 watt and may be hard to read. Use an ohmmeter to verify the values if you have trouble
identifying them.

Next, install the 1N4148 diodes. Then, the larger 1N4001 (D20). Be sure to note the band polarity on
both types. Next, install the monolithic and ceramic caps. The SIP resistor can also be installed. Be sure to note
the orientation of the SIP resistor. A small line (or dot) on the side with writing marks pin 1.

Next install U2, the 34064 (use the parts placement sheet for orientation). Then U3, the 78L05. Next,
install Q1-17. Note the orientation. Then, the variable resistors VR39 and 40. Then the Variable capacitor
C35.

Now install T1. It lays flat against the PC board and the #18 wire from the SO-239 (installed later)
will pass through the center. You may wish to use a small amount of silicon RTV or glue to hold T1 in place, but
wait until after the unit is tested before applying it in case there are problems.

Now install the socket for U1. Note the orientation of the socket. The flattened corner goes in the upper
left, toward the oscillator. Do not install the 68HC11 until later. Then the 8 MHz oscillator. Three of the
corners are rounded and one corner is square on the oscillator. The square corner is pin 1.

Next, install the tuning capacitors, C58-67. Be sure to match the values from the capacitor chart
(figure 6). Then the electrolytic capacitor, C51, on the power input, note the polarity. Then the power jack.
Now, relays K1-17 can be installed.

Lastly, inductors L1-8 can be installed on the PC board. Note that the mounting holes are offset slightly
on L3-L8 to help keep the inductors straight after installation. The inductors can be pushed in until the
windings touch the PC board. Don't forget to scrape some the insulation off the ends before trying to solder. The
#18 wire is stiff enough to support L3-L8, but RTV or hot melt glue may be needed for L1 and L2 to hold them
in place. The RTV or hot melt glue should be used if you plan to use the unit in a mobile application.

The circuit should be "power on" tested once all the components except for U1 (the 68HC11 chip) have
been installed. Apply 12 to 14 volts DC to the power input. Check for +5.0 volts on the output of the 78L05
(pin closest to U1). Current draw should be around 20 mA (anything less than 30.0 mA is acceptable). If the
volts and amps look good, you can proceed to mount the unit in the case and begin wiring the user interface. Do
not drill the mounting holes on the PC board to make them larger.

Just about any metal enclosure that is 5.5 inches deep by 8 across by 2.5 inches high will work. See
the front panel layout for ideas (figure 7). LDG also has custom finished enclosures available for around $30.

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Use the stand offs to mount the PC board in the box. Use the four mounting holes provided on the PC board, do
not drill the mounting holes on the PC board holes to make them larger.

Switch 1-7 and LED 1-4 mount on the front panel and J1 and 2 mount on the rear panel. The power
switch, SW6 connects to the two wire holes near the power jack.

The mode switch, SW7 mounts next to the power switch. It connects to J3. Grounding the pin is Auto
mode, letting it float is Semi. The 5 push buttons mount nearly in the center of the front panel and the LEDs
just push through holes. Note the polarity of the LEDs. The flattened side (on the plastic part of the LED) should
go to ground. You can see the flattened side by looking at the LED with the leads facing you. The flattened side
will be right next to one of the leads. You may want to use some silicon RTV, hot melt glue or adhesive to help
hold in the LEDs in place.

J3 is laid out on the board as a 14 pin header with 0.1 inch spacing (figure 8). A header and connector
with ribbon wire is provided for wiring the front panel components. See figure 9 for the wire designations.

The wires from the SO-239 can be left over #18 gauge wire from L1-8. You should only need about 2
or 3 inches to make the connection (figure 10). Be sure to note that the #18 gauge wire on the radio side goes
through the center of T1. Also, bring a ground wire from each SO-239 to the PC board. Be sure to scrape the
insulation off the ends of the wire before soldering.

Once everything is mounted and wired, U1(the 68HC11) can be placed into the socket and power
applied. Notice that U1 has a flattened corner that should match the socket. On power up, the AT-11 will flash
all LEDs once to indicate that everything has initialized successfully. Current draw should be around 10 mA.

Each relay draws about 30 mA when energized. If a relay energizes on power up (a sign there is a
problem), you will not be able to tell (by current draw) if the processor is working properly. No relays
should energize when the unit is first powered on. The maximum current draw is about 500 mA with all the
relays energized. Since it is rare that all relays are energized, the average current draw is about 200 mA.

Alignment: The AT-11 can be powered on or off during alignment. We recommend to leave it off so that other
components that may have problems will not interfere. If you leave it on during alignment, be sure to place the
semi/auto switch in the semi position. Otherwise, it will start tuning while you are making adjustments. Set
VR39 and 40 to the center position. With a voltmeter on test point REV (to the left of VR39) and about 10
watts applied and a dummy load or resonant antenna on the output, tune C35 for minimum DC voltage. It should
dip to just about 0.0 volts (0.1 is Ok). You MUST use a 50 ohm load (either dummy or antenna) to properly do
the alignment.

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