Assembly instructions for OZMOD ARDF PLL Controller PCB with silkscreen marking "OZMOD V3.0"

These instructions are for use with assembling the March 2004 run of OZMOD ARDF PLL controller boards that was produced by the Albuquerque Amateur Radio Club (AARC).

The build will proceed as follows:

    Install and program the CPU
    Assemble the power converter
    Test the power converter sub circuit
    Complete the build 
    Install in the RX1 and test

Mike (K5ATM) OZMOD source files

Last revised 08/22/2010

      Software:   Mike K5ATM
      Hardware: Jerry WB8WFK

      Website: Jerry WB8WFK


Caution: Some components used in OZMOD are ESD (Electro Static Discharge) sensitive. Please observe proper ESD handling procedures.

Front side view of OZMOD (V3.0)


Other related files that will assist you with assembling your OZMOD
ozmod_V3.pdf Schematic of OZMOD PLL controller
toplevel.PDF System schematic showing how to connect OZMOD to the RX1
board.pdf PCB board drawings
OZMOD_V3_parts_list.pdf Parts list



Install and program the CPU

Note: If your OZMOD board already has the CPU installed and preprogrammed as part of a group buy then go to the assemble power converter section.

Refer to the parts list while performing steps outlined in this section.


1. Install
    R25 and R26

2. Install H3

3. Install U3 PIC16F873-20/SO-ND


1.Obtain the OZMOD hex code from Mike or or mikes zip file on this website.

2. Connect the ISP programming cable to the target system. Do not connect the programmer to the computer! It is recommended that the programmer is un powered when ever making or removing connections to the target system.

3. Start the PIC programmer software. Select PIC chip load hex file and configure programmer settings as shown to the right. PIC 16F873, HS, CP OFF

Make sure that the programmer software has the LOW VOLTAGE PPOGRAMMING option disabled. LVP being enabled may cause operational problems with OZMOD. I have observed problems in other PIC based projects that were caused by this function being enabled.

4. Connect programmer to computer RS-232 port and program OZMOD.

5. Use the programmer Verify function to ensure that OZMOD is programmed.

6. Unplug programmer from RS-232 port. OZMOD is loaded.

7. Unplug ISP cable from OZMOD and continue with assembly.

NOTE: I used the Spark Fun electronics model PIC -PG2C programmer with ISP cable. The cost for this programmer was $20 when I purchased my unit. This programmer uses the RS-232 port. Caution is advised as some laptop computers have low power RS-232 ports and this programmer may not work with them as it draws its operating power from the port. I have been using it with my desk top computer that has a real RS-232 port and windows XP.

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Assemble the power converter


1. Install:

    U1 (Install this part first)
    C7 and C8


Install U1 first as capacitors C1,C2 and C3 make it hard to access U1.

Note C1,C2 and C3 are sensitive to polarity. The band marked on D1 should be on the end closest to L1

Note Do not sub low cost electrolytic for C1,C2 and C3 as these caps need to have a low ESR for the power converter to operate correctly.

2. Inspect work for assembly errors and solder bridges.


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Test the DC / DC converter

1. Verify that JP1 is not installed (to protect the PIC chip)! The PLL chip U4 should not be installed.

2. Connect a 4.5 volt power source to H2. The positive input will be pin 2 and ground will be pin 1. See schematic.

3. Connect a voltmeter to H4. The positive lead will be connected to Pin 1 and the ground lead will be connected to pin 2. See schematic. Also note the ground pin number difference between H4 and H2. This is not an instruction typo.

4. Turn on the power supply and measure the output from the DC/DC converter. It should be close to 9 volts.

5.Turn off supply.


6. Connect the positive voltmeter test lead to the Positive end of C7.

7. Turn on the power supply and verify that the 5 volt regulator is working.

8. Turn off and Disconnect the power supply and all test cables. Do not skip this testing step as a malfunctioning power converter sub circuit could damage the PLL and PIC chip!

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Continue with build

1. Install a wire jumper in JP1 position and solder in place +5 bus is now connected to the PIC chip and LCD display header.
2. Install U4 first This step starts assembly of the Phase Lock Loop and micro controller circuit.
3. Install
    C13 and R7

4. Install Crystal X1. Caution make sure X1 is elevated above the board to prevent shorts with VIA'a and circuit traces.

Note: Use hot glue to hold X1 in position above the PCB


5. Install
     C19 and C20

This assembles the loop filter for use with the RX1 receiver
6. Install
    R22 and R23

7. Install
    C11 and C14. Also use hot glue to hold X2 in position to prevent it from touching the circuit board.


8. Inspect all work. Be sure to look for any solder bridges.

This completes assembly of an OZMOD configured for use with the RX1 receiver.

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Install in RX1

You will need to obtain the following items to assemble and house the OZMOD on the RX1. Also refer to the top level schematic for wiring the assembled unit.


1 each BUD CU-124 ECONOBOX Hosing for OZMOD that attaches to RX1
1/8 inch thick sheet cork Forms weather seal between OZMOD and the RX1. Got a 12" X 26" X 1/8 " sheet at an auto parts store and cut to size. See photo 3
Sub mini toggle switch Radio Shack 275-613 Used for PLL / Manual switch (S6 on top level schematic).
2 each sub mini SPST switches. SW7 and SW1 on top level schematic One used for on /off and the other used for diode in/ out
1 each LCD display User interface and status. See OZMOD parts list
4 each sub mini momentary push button switches Radio Shack 275-1571 Used to input commands to OZMOD
1 each AA battery holder Radio Shack 270-409 Modified (switch removed) and hollow cavity area used to attach to original screws that held original 9V battery holder. Cavity cover replaced and hot glue used around outside of holder for additional support.
4 each 1.25 volt Ni - MH batteries LONG LIFE Power source.

First you will want to temporarily mount the OZMOD board to the display board using the spacers. This will allow you the hold the board in alignment while connecting the digital I/O lines. Header H5 will line up with the I/O lines of the display board. Connect the two boards together pin per using solid wire. The following pins are connected. Pin 1,2,3,4,5,6,11,12,13,and 14. See top level schematic.

Next connect your OZMOD controller to the 4.5 volt power source. Turn on the power source and you should get the welcome message. Shortly thereafter the operating display (VFO A/B frequency, Time on course, TX # and power status) should appear. If this step is ok you are ready to proceed.

After the display is mounted in the case connect the push button switches and all other I/O. Diode D1 on the top level schematic is mounted on the pins of SW7.

Key Functions
As marked on system schematic
Blue indicate alternate switch functions

The Radio Shack AA battery holder was modified to use the original 9 volt battery clip mounting holes and screws. The switch on the AA holder is removed and the holder is re-wired.

A hole was drilled on one end to allow the wires to exit the holder and enter the original hole that the 9V battery wire originally used to enter the RX1. The wire and both holes are covered with hot glue to protect and form a seal.

Also the hole that contained the original on / off switch on the radio shack AA holder was sealed using hot glue.

After the two mounting screws that attach the AA holder to the RX1 (inside the original AA holder switch cavity)are secured, they are covered with hot glue to prevent them from backing out. The switch cavity cover was reattached after this procedure.

Photo 1

This photo shows the housing for OZMOD and the two threaded spacers used to attach the housing to the original RX1 Cover. Note the two additional holes drilled in the original cover to allow wires to enter the RX1 cavity.

Photo 2

This photo shows how OZMOD is attached to the top of the LCD display (the hole pattern of OZMOD matched that of the display. Also the I/O header on OZMOD is over the one on the LCD display. This allows the shortest possible wire runs to be used.

Also nylon washers are used to prevent mounting hardware (nuts) from making contact with any circuits on the OZMOD board.

Notice that RG-174 U coax is used to feed back the LO VCO to OZMOD. A coax must be used for proper operation also refer to photo 1 and the top level schematic to see how the coax is attached at the RX1 end.

Twisted wire is used to make the power connections and VCO control voltage connections between OZMOD and RX1. Connect the return lines to the RX1 ground plane as close to the desired signal node as possible

Photo 3

Alignment and checkout.

1. After the unit is wired and before you re-assemble, place the PLL / RX1 switch to manual position to allow the POT to control the RX1 frequency. Verify that the RX1 covers the desired range of frequencies as connecting the coax cable to TP1 may have affected the VCO slightly. If required follow the instructions in the RX1 manual to get the desired coverage.

2. Place the switch in PLL control and if every thing is assembled correctly OZMOD will be controlling the RX1.

Note: Never operate OZMOD from 4 - 1.5Volt AA batteries. This can stress the power converter possibly causing damage to this sub circuit. Away's use 1.25 volt Ni-MH cells as the discharge curve will give you a very long operating time (over 10H). You can use the diode switch to reduce the voltage during the first two hours of operation while operating on the Ni-MH battery peak which occurs after charging. Some RX1's do not like to operate in the high 9s. Not an issue with the foxfinder-80. After about 2H the battery will be off the peak and on the flat part of the discharge curve and the diode can be switched out. A simple design was used for the power converter to reduce EMI

Assembled OZMOD unit ready for action. I made a cover in Microsoft power-point, then printed it on viewgraph transparency stock using a color laser printer.

73's and enjoy!

We also have another modification for the RX1. Over A year ago we replaced the ceramic filter in the high IF with a crystal filter. Since then off hunt frequency QRM from packet and a mountain top voice repeater has been eliminated.

Photo 4

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