LDG QRP Assembly Manual

QRP Automatic Antenna Tuner

Assembly Manual

Ver 2.0c

LDG Electronics

1445 Parran Road St. Leonard MD 20685

Phone: [phone] Fax: [phone]

e-mail: [e-mail]

http://www.radix.net/~ldg

Introduction: The QRP autotuner is a full featured auto or semi automatic antenna tuner designed for HF

(1.8 to 30 MHz) transmitters using 0.1 to 10 watts. It was modeled after the AT-11, a 100 watt version of
the auto tuner that first appeared in the January 96 issue of QST magazine. Both tuners use a switched "L"
configuration with 256 capacitor, 256 inductor and Hi/Lo-Z settings to provide over 131,000 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). It can be optimized to work with balanced line fed antennas (and
random wires) with a 4 to 1 or 6 to 1 balun (not provided). Tuning time of the QRP version has been improved
to between 0.1 and 3.0 seconds with an average time of 1.5 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 (semi line is grounded), the tuner will only seek a match when the tune
input line is grounded. Both modes require that more than 0.1 watts of RF power be present. Up and down input
lines are provided for fine tuning the inductors and capacitors and can be used in either mode.

Four outputs to LEDs provide an indication of SWR and status. 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.

Building the Kit: The QRP autotuner is a small sized project. It should take the average builder an

evening or two to complete. We averaged 2 hours for populating the PC boards for the prototypes, but it may
take another hour or two to install it inside your favorite transmitter or enclosure. Besides the normal
building tools needed (small soldering iron or soldering pencil, wire cutters, screwdriver, ect), the only test
equipment needed is an HF transceiver, dummy load (or resonant antenna) and voltmeter.

Just about anything that the PC board will fit into will work as an enclosure. A metal enclosure is not a
requirement, it can be plastic. LDG has a package that includes a custom enclosure made by Ten-Tec Inc and all
front and back panel hardware (SO-239 connectors, switches, LEDs) for $25 plus $6 shipping.

Kit Assembly: Before starting, you may want to get a copy of the QST article where the original AT-11

first appeared. Although not needed for construction of the QRP 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

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QST, 225 Main St., Newington CT 06111. We've included the charts and tables from the article (modified for
the QRP version) needed to build the kit in this manual.

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 about 150 parts and 500 solder connections, so take your time.

Once familiar with the parts, start with the nine T-50 toroids (they are red and just over a half inch
in diameter). Take care to not drop them, they will break. Use the number #24 gauge wire provided to wind
L1-8. For consistency, we count one turn when the wire passes through the center of the toroid. L1-4 just
loop at the bottom of the toroid (figure 2). L5-8 are evenly spaced around (figure 3). L8 is a double toroid,
two toroids held together with the winding around both of them. Use the inductor table to cut the wire to length
(figure 4). Wind each toroid in the same direction as shown in the diagrams. Note that L1-4 wind in one
direction and L5-8 wind in the other. The PC board is laid out with offset solder pads for the toroids. If you
wind them backwards, the offset will not match. 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 together or just 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 comes from under T1 and the wires on the right side comes 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.

Notice that some of the silk screen markings on the PC board 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.

The 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.

After the resistors are installed, install the 1N4148 diodes. Then, the larger 1N4001 (D3). Be sure to
note the band polarity on both types. Next, install the groups of monolithic and ceramic caps. This includes the

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tuning capacitors, C25-34. Be sure to match the values from the capacitor chart (figure 6). The SIP resistor
pack can also be installed. Be sure to note the orientation of the SIP resistor (the tuner will not work if it is
installed backwards). 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 R23 and 24. Then the Variable capacitor C1.

Now install T1. 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. T1 will lay flat against the PC
board. The wire that carries the RF input from the transmitter will pass through the center of T1 and solder
directly to the PC board.

Now install the socket for U1. Note the orientation of the socket. The flattened corner goes in the lower
right, toward the crystal. There should also be an arrow inside the socket that will point away from the relays
(see the parts placement sheet). Do not install the 68HC11 until later. Then the crystal X1. Now, relays K1­17 can be installed. Then the two electrolytic capacitors, C9 and 18, note the polarity.

Lastly, inductors L1-8 can be installed on the PC board. Note that the mounting holes are offset slightly
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 the insulation off the ends before trying to solder. The #24 wire may be
stiff enough to support L5-8, but a non-acidic RTV or hot melt glue may be needed for L1-4 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.

Checkout: 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 2.5 mA (anything less than 10.0 mA is acceptable).
If the volts and amps look good, you can proceed to mount the unit in a case or inside a transmitter and begin
wiring the user interface. 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.

J3 is laid out on the board as a 14 pin header with 0.1 inch spacing (figure 7). A header is provided for
wiring to the user interface. Depending on your particular installation, you may only want to connect a single
wire for the Tune button. If you desire the auto feature, you will have to either wire the Auto line to ground to
enable that mode or connect that line to a toggle switch to allow selection of modes. Likewise, you may not need

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the SWR or tuning indicators in your installation, but they are there if desired.

A ribbon cable is provided to make front panel connections (see figure 8 for wire assignments). Note
that when plugged in, the wire should extend away from the microprocessor. The two ground wires (pin 13 and

14) should be connected to the front panel ground wire (see figure 9).

The Auto/Semi input line is ground activated. That is, when the line is grounded, it will be in the Auto
mode. If it left floating, it in the semi mode. The Tune, Cap Up, Cap Dn, Ind Up, and Ind Dn are also ground
activated. Grounding the line will activate it. The LED current is supplied from the processor. 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. See figure 9 for details on
wiring the front panel.

The typical minimum installation was envisioned to be just the Tune line run to a momentary contact
push button on the front panel of your transmitter. Nearly most of the time, the up / down buttons for the fine
tuning are not needed. The unit is set to find a match of less than 1.5:1 and nearly always does.

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. Be careful here, it
backwards and it
the chip should be upside down while looking at the board while the inductors are on the top. On power up, the
unit will flash all LEDs (if used) once to indicate that everything has initialized successfully. Current draw
should be around 10 to 15 mA.

Each relay draws about 12 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 190 mA with all the
relays energized. Since it is rare that all relays are energized, the average current draw is about 75 mA.

will

destroy the processor if it is powered on while in the socket backwards. The writing on

will

go in

Alignment: The tuner can be powered on or off during alignment. We recommend to leave it off so that

other components that could possibly have problems will not interfere. If you leave it on for testing, be sure to
place the Auto/Semi switch in the Semi position. Otherwise, it will start tuning while you are adjusting. Set
R23 and 24 to the center position. With a voltmeter on test point REV (marked on the silk screen) and about 5
to 10 watts applied to the input and a dummy load or resonant antenna on the output, tune C1 for minimum DC

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voltage. It should dip to just about 0.0 volts. You MUST use a 50 ohm load to properly do the alignment. If the
load is not resonant, you may get more than 0.0 volts on the REV test point. Anything less than 0.2 volts will
provide satisfactory results.

Then, apply 5 to 10 watts to the input. Adjust R23 for 2.5 (2.3 to 2.5 is Ok) volts on test point FWD.
Move the dummy load to the input and apply 5 to 10 watts to the output. Adjust R24 for 2.5 volts on test point
REV. Be sure to not go over 2.5 volts on either test point.

If you don’t get 5 watts out of your radio, use 2 to 3 watts and adjust for 1.5 volts for both. That's it,
the tuner is now ready to be placed on the air.

Operation Notes: In general, the tuner operation is straight forward (you push the tune button and it

finds a match) and works as described in the introduction section of this manual.

The software for the QRP version was modified slightly from the original AT-11 to help reduce power
consumption. When the tuner is in the semi mode, the processor will go to sleep after it finds a tune. This
reduces power consumption by about 20 mA once a match is found. Note that while the processor is asleep, the
LEDs (if used) will also be disabled. The processor can be woke up by pressing the tune button once while no
RF is present. It can also be forced to go to sleep by simultaneously pressing both down fine tune buttons (if
used).

When the tuner is in the auto mode, it does not go to sleep, it stays awake to monitor for an SWR of
above 3:1. Again, it can be forced to go to sleep by simultaneously pressing both down fine tune buttons (if
used) and be woke up by pressing the tune button once while no RF is present.

Although specified for 10 watts, the actual maximum operating power can be as high as 30 watts (at
50% duty cycle). The relays are rated for over 30 and the toroids will handle about 50, but the RF input
power should never exceed 30 watts..

If the LEDs are installed, they will indicate SWR whenever there is more than .1 watts of forward
power. If you press the tune button and there is less than .1 watts of forward power, it will not go to the tune
algorithm and all LEDs will flash once.

You can use SSB to provide the power for tuning. Just press your mic and say something (like
“Ahhhhhh”) until the unit stops tuning (somewhere between .1 and 3 seconds). If the tuner has a hard time
finding a match or doesn't find 1.5, try using a CW or AM carrier.

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