PROVISIONAL DESCRIPTION

21/09/2026 : waiting to validate a later iteration of the PCB before a full description is published.

nb. Prototype version shown

A 2m micro transmitter for casual ARDF events, demonstration or training.

The transmitter is incorporated into the hub of a cross dipole with plug-in antenna elements, and then ready to hang from a tree branch.

Accessible battery which can be removed when unused.

Approximate output 20mW.
Tested range at 2km , audible S5 across a clear path using a simple ARDF receiver.

Sends MO continuously, or either MOe, Moi, MOs, MOh, MO5 in a 1 minute slot. Specific MO ident, is set in eeprom memory, and can be user changed.

Default output is 144.65Mhz from a ICS501 8x multplier using a standard 18.08Mhz crystal.

Dip switch settings

OFF 5 TX classic format. Transmitter on for 1 minute every 5 minutes. Option to automatically synchronize 5 transmitters sequentially.

ON 2 TX training format. Transmitter on for 1 minute every 2 minutes. (no synchronize option)

Manually start.

(5T and 2TX modes) The transmitter starts immediately. For multiple transmitters, manually switch on each transmitter in order every 1 minute, or switch on using an accurate time piece.

Automatic Synchronized Start, with a 90 minute delay.

The delay allows the event planner to seed each transmitter without revealing its location before the start of an event.

Requirement- A daisy chain of 2.1mm power plugs, (widely available pre-made). Install a switch on the female socket end, so it can can short and open the lead.

• Monitor the transmitters with a 2m receiver.
• Insert the daisy chain plugs into all the Transmitters.
• Close the shorting switch.
• Switch on all the connected transmitters.
• Open the shorting switch at exactly 90mins before the first transmitter (MOe) is required to heard. Each transmitter will then broadcast a single burst of its ID at 5 second intervals.
  The burst sequence is repeated each 10 minutes during the 90 minute delay period.

Changing the MO ident.

Can be MO, MOe, MOi, MOs, MOh or MO5

• Monitor the transmitters with a 2m receiver.
• Set the DIP switch to ON
• Hold down the tactile button switch then … Power switch ON … release button.
• Transmitter will broadcast warning dits and then the current MO ident. eg MOe.
• Press the tactile button to cycle through each MO ident until the required one is broadcast.
• Switch off the power.
• Return the DIP switch to the required position.

Changing the Callsign.

By default, the end-of-transmit callsign is set to ‘ARDF’ and is held in EEprom memory. There is no function to enable manual user editing of the callsign. It can however be edited using a PIC programmer.

• Read/Load the PIC program into the PIC programmer.
• Edit the relevant EEprom bits
• Re-program the PIC.

EEprom memory location 0 stores the MO ident. (eg. MO=0, M0h=04).
EEprom memory location 1 onwards stores the callsign up to a final bit value of ff.

See below for the Morse encloding (HEX), with acknowledgment to VE2EMM for the source code.

eg. G3ZOI is :- 0b 38 13 0f 04 ff

MORSE ENCODING

One morse character per BYTE, bitwise, LSB to MSB.

0 = dit, 1 = dah. The byte is shifted to the right bit by bit, until the last 1 is left, this 1 is an END OF CHARACTER indicator. A maximum of 7 elements can be encoded, (error) is excluded.

• / 29
• 0 3f
• 1 3e
• 2 3c
• 3 38
• 4 30
• 5 20
• 6 21
• 7 23
• 8 27
• 9 2f
• A 06
• B 11
• C 15
• D 09
• E 02
• F 14
• G 0b
• H 10
• I 04
• J 1e
• K 0d
• L 12
• M 07
• N 05
• O 0f
• P 16
• Q 1b
• R 0a
• S 08
• T 03
• U 0c
• V 18
• W 0e
• X 19
• Y 1d
• Z 13
• EOM ff = End of Callsign