HamOperator K9EQ AH-4 User manual

K9EQ AH-4 Universal Interface Rev. 5 Page 1
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K9EQ AH-4 Universal Interface
User’s Manual

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Table of Contents
Forward..............................................................................................................................................................................................................................3
Warning.............................................................................................................................................................................................................................3
Description and Introduction.........................................................................................................................................................................................3
Board History...............................................................................................................................................................................................................3
Why use the AH-4?.....................................................................................................................................................................................................4
Basic Interface..............................................................................................................................................................................................................4
Full Interface ................................................................................................................................................................................................................5
Construction......................................................................................................................................................................................................................5
Basic Version...............................................................................................................................................................................................................6
Optional components ..................................................................................................................................................................................................7
Construction Notes ..........................................................................................................................................................................................................8
Component Identification...........................................................................................................................................................................................9
Verification.......................................................................................................................................................................................................................9
Initial Basic Version Checkout.................................................................................................................................................................................9
Initial Full Version Checkout..................................................................................................................................................................................10
Final Basic Version Checkout.................................................................................................................................................................................10
Final Full Version Checkout....................................................................................................................................................................................11
Circuit Description ........................................................................................................................................................................................................11
Installation.......................................................................................................................................................................................................................12
Operation.........................................................................................................................................................................................................................14
Basic Interface............................................................................................................................................................................................................14
Tuning.....................................................................................................................................................................................................................14
Setup........................................................................................................................................................................................................................15
Power output control using AM mode..............................................................................................................................................................15
Full Interface ..............................................................................................................................................................................................................15

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Troubleshooting.............................................................................................................................................................................................................16
Schematics ......................................................................................................................................................................................................................18
Parts List..........................................................................................................................................................................................................................21
AH-4 Radio Interface Theory of Operation..............................................................................................................................................................23
Forward
An updated version of the manual may be available. Check with www.hamoperator.comfor updates as well as additional information
and feedback from other users. This product may require modifications from the stock design to work with your radio. Information on
interfacing with different radios will be published when available.
Warning
It is possible to damage your equipment by using the interface described in this document. Use of this document, the AH-4 Universal
Interface, or any information from www.hamoperator.comis done at your own risk. Do not use this information unless you are willing
to assume all responsibility. The kit employs components that can be damaged by electrostatic discharge.
Description and Introduction
Hello,and thank you for your interest in the K9EQ AH-4 Universal Interface. The interface is designed to allow you to use the Icom
AH-4 remote automatic antenna tuner with virtually any HF rig.
I started this project after I purchased an Icom 706 and AH-4. I was very impressed with how well the tuner worked. It was almost
effortless to build wire antennas, throw them in the trees, and work plenty of DX. The first contact with my first antenna (a loop I built
in the garage) was with Belgium!
I looked at other antenna tuners on the market and concluded that the AH-4 was the one I wanted to use. It is well designed, rugged,
and priced very competitively. From my point of view, it had only a few disadvantages. The documentation that comes with the tuner
is not very good and I couldn’t use it with my other radios. While I really like the 706, I’d like to be able to use the tuner with my
Yaesu FT-990.
I addressed the first disadvantage by publishing information about the AH-4 at my web site, www.hamoperator.com.
The second disadvantage is addressed by the K9EQ AH-4 Universal Interface.
Board History
The first version of the interface was the “basic” version. It would tune the AH-4 when the TUNE button was pressed, but the user had
to set the rig to a carrier mode and adjust the output to 5-15 watts. I presented the board to a good friend of mine, K0ZE, for review.
His comment, “You could get twice as much stuff on the board.”
Well, being a ham radio operator and being cheap–er…. I mean frugal –I couldn’t let board space go to waste! Hence, some
improvements were made. The first improvement was to have the board generate a 1 KHz tone. If you were in SSB, this would
eliminate the need to change modes. You could also adjust the tone level to control the power output (assuming speech processing is
off). The second addition was to provide an ALC output to the radio. This 0 to–4 volt signal would cause the transmitter power to roll
back to 5-15 watts when the tuner was engaged. (More on this later).

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Getting a negative voltage from a positive supply was a bit tricky. Once again K0ZE came to the rescue. “Why not use one of those
RS-232 chips that generate their own negative and positive voltages?” So a MAX 232 was placed on the board.
It’s very sad to see an RS-232 chip with only one port in use! That’s when I added a computer interface to allow logging and rig
control programs to communicate with the rig.
Well, if you have RS-232 and you can key the transmitter, you almost have everything you need to interface the computer’s sound
card to the radio. I would, after all, like to run PSK31. A few resistors and capacitors later, I was running PSK31.
Proud of my new board, once again I showed it to K0ZE for his approval. His comment, “You could get twice as much stuff on the
board.”
While K0ZE figures out what features should be added, I now have a “full” interface that let’s me use the AH-4 with virtually any
radio, simplifies the tuning process, provides computer control of the radio, and let’s me run PSK31.
Why use the AH-4?
The K9EQ AH-4 Basic Universal Interface allows the use of the Icom AH-4 and similar antenna tuners with most HF rigs. The AH-4
is intended to be used with certain late-model Icom radios, such as the IC-706 and IC-746. The AH-4 communicates with the radios
using two control lines. Since the radio and the AH-4 can communicate, the AH-4 offers the following advantages over conventional
wide range automatic antenna tuners:
oTuning is accomplished using about 10 watts of power from the radio.
oThe power from the radio is split between a dummy load and the antenna thus the radio sees a maximum SWR of 1.1:1 while
tuning –this prevents damage to the rig’s finals.
oA maximum of 350 mW is radiated during tuning –minimizing QRM. Other hams will appreciate your use of the AH-4.
oTuning is never done under full load. This can prevent premature failure since the contacts of the tuning relays never switch
while high voltages are applied. There are over 20 relays in the AH-4!
oThere is positive indication that tuning has been accomplished.
oThe tuner can be disengaged at any time–permits receiving on other frequencies.
oThe best “bang for the buck”. The AH-4 is less expensive than similar tuners on the market.
Unfortunately, those without the appropriate late model Icom HF rigs have not been able to take advantage of the AH-4. That is, until
now. The K9EQ Universal AH-4 Interface allows the AH-4 to be used with virtually any HF rig. Once installed, the tuning operation
is simple.
There are two versions of the interface: a “basic” and a “full” version. The basic version allows the AH-4 to interface with almost
every HF rig. The full version adds an RS-232 and a computer sound card interface.
Basic Interface
Some people may not actually want all of the K0ZE-inspired features. For these folks I have broken the board down into the original
“basic” interface and a “full” interface. The following tuning process is used with the basic interface:
1. Set the rig to the desired HF frequency.

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2. If you are not in SSB or have not connected the audio interface, change the mode to one that emits a carrier (AM,
FM, or CW) and adjust the power output to about 10 watts (5 –15 watts will work). (If you are in SSB, you will
need to turn off speech processing.)
3. Push the TUNE button. The AH-4 will automatically tune. A status light indicates that the AH-4 is tuning and the
final tune status.
4. Reset the rig’s mode/power (if it was changed) and begin operating. Note that any many cases it is only necessary to
retune when changing bands.
To be compatible with the K9EQ Universal AH-4 Interface, the HF rig should have:
oA convenient means of adjusting output power.
oAvailability of a mode that emits a carrier (AM, FM, or CW)
oA keying line that operates at a maximum of +20 volts and 100 ma. (The interface will pull this line to ground when it needs
to key the transmitter.)
oThe radio generates a 1 KHz tone when tuning. This allows the use of SSB modes. If the speech processor is turned off, it
may not be necessary to adjust power output when tuning. (Note that this feature mayor may not work reliably depending
upon how stable the rig’s output is for a given audio level.)
Full Interface
The full interface adds the following features to the basic interface:
oThe interface generates an adjustable negative ALC voltage. This reducesthe transmitter’s output when tuning. (Note that
this feature could require frequent adjustment since the radio’s characteristics may change with temperature and voltage.)
oAn RS-232 interface that allows computer-based rig control and logging programs to interface with the radio. The interface
can be used with Icom and Yaesu radios. (Kenwood should work also but has not been tested.)
oThe RS-232 interface will key the radio when DTR is asserted. This allows a computer sound-card based program, like
Digipan, to key the radio.
oA computer sound card–radio interface has been implemented. This allows SSTV, RTTY, CW, PSK31, and other sound
card-based software to work with the radio.
For more information, please visit www.hamoperator.com. I am always interested in hearing your comments about this manual, the
interface, the AH-4, or any subject you care to discuss.
73’s,
Chris, K9EQ
Construction
The K9EQ AH-4 Universal Interface may be built using prototype construction techniques or by using the printed circuit board. These
assembly instructions assume that you are using the printed circuit board Rev. 2.
Construction options:
The board may be built with the one of the following three options:

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oTUNE and UNTUNE buttons on the PCB
oTUNE and UNTUNE buttons on the PCB and also mounted externally
oExternal TUNE and UNTUNE buttons
The following options are also available
oLEDs on PCB
oLEDs mounted remotely
External buttons and LEDs allows more flexibility in mounting, while onboard components make it simpler to build and get working.
Basic Version
The basic version requires the following parts:
C1, C2, C3, C4, C5, C6, C7, C8, C17, C18
D1, D2, D3, D4, D5, D6
J1, J2, J3
L1, L2, L3
Q1, Q2, Q3
R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, R13, R14, R15
U1, U1S, U2
X1
PB1, PB2

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Fig. 1 Assembled Basic Board
Optional components
The following components are not required and may be substituted as follows (with the corresponding change in protection, RF
immunity or feature). Required substitute action and change is indicated.
F1 –short, provides short circuit protection.
D6 –short, provides reverse voltage protection.
L1-L3 –short, provides RFI protection
D4, R6 –open, provides power on indication.

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Figure 2 PCB Component Layout
Pin 1
Pin 1
Construction Notes
Electrostatic warning: U1 and U3 may be damaged by electrostatic discharge. Ground your body using
the appropriate equipment prior to handling these components or the board once these components are
installed.
View the board component side up with lettering upright. Refer to Figure 2 for parts placement.
Use the photograph on the cover of this manual for additional parts placement assistance.
It is recommended that you use a DVM to verify the component values of the resistors. Amagnifying glass may be useful for reading
other component part numbers and values.
When looking at the front (flat side) of the 78L05 with the pins down, the pins from left to right are: Output, Ground, Input.
When looking at the front (flat side) of 2N3904 or 2N3906 with the pins down, the pins from left to right are: Emitter, Base, Collector.

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The “narrow” side of Q1-Q3 and U2 represent the flat side of the device.
All components mount on the top side of the board.
U5 and R24 are not used. These are on the board to allow for future software development with non-volatile memory.
The short pin on the LEDs is the cathode and is attached to pin 1 (square pad).
J1, J2, and J4 can use right angle connectors. This may simplify connection depending upon how the board is mounted. See the parts
list. The connector kit includes right angle connectors.
The basic version requires a jumper from pin 9 to 16 of U3. This is done to prevent the rig from keying up as the input to the
microprocessor floats.
Component Identification
Component Identification or Marking
100 ohm resistor brown-black-brown
220 ohm resistor red-red-brown
1 k resistor brown-black-red
4.7 k resistor yellow-violet-red
100 k resistor brown-black-yellow
22 pf capacitor 22
.001 uF capacitor 102
.1 uF capacitor 104
10 uH inductor Green body brown-black-black
Verification
In the following steps, a 9 volt battery may be used as a power source when the board is not connected to the AH-4 and U3 is
removed.
Initial Basic Version Checkout
After construction is complete, perform the following verification steps:
1. Verify that all components have the correct values and are wired according to the documentation.
2. Apply approximately 13.8 volts to the interface (J2 pin 5 = 13.8, J2 pin 4 = GND). Verify that the power LED lights. If it
does not, confirm correct assembly of U2 and associated components. Verify input and output voltages with a DVM.

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3. Apply approximately 13.8 volts and verify that the status LED flashes. If not, confirm correct assembly of the status LED and
the oscillator circuits (X1). Verify with a DVM that +5 volts is applied to U1 pins 4 and 14 and that ground is applied to U1
pin 5.
4. Install the preprogrammed PIC16C54C microprocessor at U1 into the IC socket. Be sure to orient pin 1 towards the upper
right. Pin 1 is indicated by a small circular dimple on the top of the chip. Be careful not to bend the leads under the chip while
installing it. Make sure all 18 pins are properly seated in the IC socket.
5. Attach a resistor (1-10K) between 13.8 volts and START-OUT (J1 pin 2). Press the TUNE button and apply power. Release
the TUNE button. Examine the START-OUT signal with a DVM. It should be at approximately 13.8 volts and decrease to
approximately 0.6 volts or less when the TUNE button is pressed.
6. Attach a resistor (1-10K) between 13.8 volts and RIG-TX (J1 pin 1). Press the TUNE button and apply power. Release the
TUNE button. Examine the TX-OUT signal with a DVM. It should be at approximately 13.8 volts and decrease to
approximately 0.6 volts or less when the UNTUNE button is pressed.
7. Press the TUNE button and apply power. Release the TUNE button. The status LED should be off. Short the KEY-IN line to
ground. The status LED should turn on.
Initial Full Version Checkout
1. Plug in U3. Attach the board to a 12 volt power source.
2. Verify that the voltage at U3-2 is approximately +8.5. If not, verify installation of capacitors C9-C12. Verify installation of
U3. Confirm that outputs are not shorted.
3. As above, but verify the voltage at U3-6 is approximately –8.5 volts.
4. Turn the power off. While pressing the TUNE button, apply power. Measure the voltage J2-2. While pressing TUNE, adjust
R12. The voltage should be adjustable over the approximate range of –0.75 to –0.5 volts. The voltage should go to zero when
TUNE is released. Press TUNE and adjust R12 for minimum output (full counter-clockwise).
Final Basic Version Checkout
This completes testing of the interface board. Connect it to the power supply, rig, and AH-4. Perform the following in-circuit tests.
1. Turn on the power supply. Adjust the rig for no power output (i.e., RF and mic gain turned down, SSB mode). Press the
TUNE button. Verify that the rig switches to transmit for about one second and then returns to receive. The status LED
should be flashing. If this test fails, verify that grounding the TX-OUT line causes the rig to transmit. Make darn sure you
didn’t connect the TX-OUT line to something that either has voltages much higher than 13.8 or something that can source a
lot of current–like the power supply.
2. Place the rig in AM, FM, or CW mode. Key the rig and adjust the power until it is about at 10 watts. Unkey the rig. Press the
tune button. Verify that the rig keys on for several seconds then unkeys. Verify that the status light is on. Check the SWR. It
should be less than 1.5:1. If this test fails, check wiring between the AH-4 and the interface.
3. Turn the RF power up to 120 watts (or whatever the radio will do, whichever is less). Transmit. Verify that the status light
remains on and the SWR is less than 1.5:1. If not, verify that RF is not getting into the control lines.
4. Reduce the RF output of the rig to less than 10 watts. Change to a frequency where it is known that the antenna has a high
SWR. Press the UNTUNE key and verify that the status light goes off. Key the rig and verify that the SWR is higher.