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New, the Firmware is available free on this page
If you do something with this let me know by an Email: on7fi@skynet.be

Concept :

This device computes distance between two QTH LOCATORS as well as antenna azimut. For short distances, precision is limited by the accuracy of World Wide Locator systems.

Zero distance is given for two LOCATORS in the same square. In this case, contest regulations usually give a certain number of points.

Computing precision depends on mathematical routines. QTH-mate provides the same accuracy as most PC programs.

Users Instructions:

Hit 'Enter-ON' to switch on device. Display shows 'Power ON'. You now have a delay of 30 seconds before automatic power off.
To enter 'My Locator', after power-on, push the left bottom switch until 'My QTH Locator' appears on display. Hit different keys to enter your locator.
Hit'Enter' once to store data in Eeprom memory. Your device is ready for use.

In 'Select a Locator'-mode, you have 4 minutes to enter a second locator, before automatic switch off.
'Enter' initiates computing, all other keys send to 'Select a Locator'-mode.
Push and Hold a key for several seconds for manual switch-off.

The device can be powered by an external 8 to 12v DC source. Input voltage is regulated internally to 5v. Power is dissipated accordingly.

While changing battery, the reference Locator remains in memory. Accidental polarity inversion does not damage the circuit. Battery should always be insulated by means of its plastic sleeve, to avoid short circuits.

Specifications :

Weight : without battery : 155g - with battery ~ 190g.
Power : 9v internal battery or 8 - 12v external supply.
Current : 12 mA computing or keyboard access.
8 mA stand-by
.1 µA OFF-mode

Schematic diagram

Schematic diagram download in pdf

Componants listing

PCB Layout

Silkscreen Layout

QthMate download here the firmware to put in the 80C52

The understanding of the schematic is easy. Each of the top 6 pushbuttons increase the corresponding character on the display 0,1, 2, 3,... including the letters and each of the bottom 6 pushbuttons decrease the corresponding character.

The pushbutton S13 labelled ENTER-ON has 2 functions. The first is the power on. When depressed, the base of the V2 PNP transistor is connected to the ground, which make it conductive and the battery voltage is then connected to the voltage regulator N1. This regulator lower the battery voltage from around 9V to 5V and the delivered current start the 87C52 micrcontroller. After the reset time, the microcontroller put a high level (5V) on pin 15 to saturate the V3 transistor. This one replace the action on S3 which can be now released, the power supply stay on the circuit. It is now the microcontroller which can choose the moment of his power off.

The remaining circuit is simple, the microcontroller drive a 2 lines / 16 characters LCD display to indicate the commands and the results.

A serial EEPROM memory (24C02) store the reference LOCATOR to avoid to introduce it each time you turn on the QTH mate. The modification and saving of the reference LOCATOR is explained in the user manual.

The crystal oscillator is simply made of 2 ceramic capacitors and 1 small flat Xtal. The reset circuitry is classical with one diode for the fast discharge of the capacitor in a way that a reset is done after any short power interruption.

PCB Cu side

L'implantation :


Assembly :

Click here to download the assembly drawing.

The PCB, the programmed microcontroller 87C52 or the LCD display can be ordered separetly.

PCB = 10 € + 2.1 € postage

87C52 = 10 € + 0.7 € postage

Display = 12 € + 2.1 € postage

U can pay via PayPal with my Email : michel.dewyngaert@skynet.be


If you are interested, contact us ON7FI or ON4KEN

Some Pictures


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