by Andras Paal, HG0HK Stockholm ARDF Club (SRJ) DEC 2018

Beginning with the 2012 ARDF World Championships in Serbia, two new events are being added; Sprint and Fox-Oring.
For ARDF Sprint and Fox-oring training sessions and competitions an automatic 3.5 MHz transmitter has been designed and built according to the IARU Region1 ARDF Rules -V2.10B/2012.

The new transmitter's timer is compatible with the earlier SRJ one (Olle Nilsson, SM0KON, MINI-FOX/3.5, 2007, ) and uses a Montreal Fox Controller.

Twelve transmitters were used and tested in Sprint competitions in  Stockholm, April 2012, Hungary: AH Cup, April 2012, the Nordic ARDF Championships 2013, Sweden and also in the Foxoring competitions, Stockholm, 2013.

For the Finnish ARDF Radio Clubs twenty ARDF Sprint/Foxoring 80m transmitters have been built and twelve for the Hungarian MRASZ(2014). One set of the transmitters has been tested in the Hungarian Sprint and Foxoring Championships 2014 as well as in Stockholm.


Power supply: built-in Li-Ion accumulator 3.7 V/3400 mAh
Charger: built-in with automatic, supplied from any 5 V DC source
Charging current: 300 mA
Operating temperature range: -10 ... +50 °C
Dimensions: 70 (W) x 50(H) x 110 (D) mm
Weight: 200 g

Carrier frequency: 10 channels (3.51 ... 3.60 MHz)
Mode: A1A (CW)
Output RF power: HI: 1.7 W, LO: 0.5 W
DC current: max 0.8 A (@4V)
Internal loading possibility: 47 pF series with 68 Ohm
Antenna: vertical wire 7m + 2x7m counterpoises
                Fox-oring (Fo): 0.3m vertical wire
Antenna tuner: manual with output power indication
Total hunt time: 6 hours (software limited)

Transmitted codes: MOE, MOI, MOS, MOH, MO5, MON, MOD, MO and S 
Keying speed: 60 or 75 PARIS 
Continuous (Fox-oring)
12s transmit, 48s space (Sprint) 
60s transmit, 240s space (Classic 1/5 min) 
60s transmit, 360s space (Classic 1/7 min) 
Time base accuracy: ±10 ppm (1s/day)
Start delay: 0...21 hours, in 3 hours increments.

See Sprint/Fox-Oring circuit diagram, Board layout (reference), Front panel, Code table, Parts list


The modified Montreal Controller allows the PIC to be programmed and then tested without having to remove the PIC16F628A.
I got programming help from Geza Szekely, Jozsef Kujbus, YO5AT and Istvan Vanyi, YO5OFJ.
Here is the code for PIC controller type PIC16F628A (628.HEX).


1958 I started my ARDF "career" constructing and competing with a 144 MHz super-regenerative receiver using a 6J6 tube in Hungary.

1959 I passed the UHF-VHF examination and got licensed as HG0HK in 1961.

1964 I designed a 144 MHz ARDF receiver using 2SA229 transistors.

1968 We designed a TTL controlled timer for ARDF transmitters using prototype ICs from Texas Instruments. We built 500 of them for ARDF Clubs in Hungary. The timer and 3.5 MHz transmitter was published in Radiotechnika, 1971 (in Hungarian).

1973  7th European/IARU R1 ARDF Championships in Hungary

Transistorized, automatically controlled fox transmitters, published in Radiotechnika, 1971 7/8 were used. The five foxes called MOE up to MO5. Remarkable is the statement in Funkamateur 1973/11, and DL-QTC 1973/12, that the five foxes worked, both at 80 m and 2 m, all on the same frequency. Only the finish beacon (MO) that was constantly in the air worked on a different frequency. The transmitters had a time control which was derived from a crystal oscillator with TTL frequency dividers, and shift registers. Also the call signs were transmitted automatically.

1986 I won Individual and Team silver medals in the 144 MHz competition in Yugoslavia, 3rd World ARDF Championships.

2008 Team leader and competitor in the Hungarian ARDF team; 14th World ARDF Championships, Korea ARDF.

2010 16th World ARDF Championships, Croatia; competitor in the Swedish ARDF team.

2011 Montreal Fox Controllers program written for sprint and fox-oring events for SRJ Club 3.5 MHz ARDF transmitter (Olle Nilsson SM0KON, MINI-FOX/3.5, 2007, ).

2012 Twelve ARDF 80m transmitters were tested in sprint competitions in Stockholm and in Kecskemet, Hungary.

2012 Team silver medal in the 3.5 MHz competition in Serbia, 16th World ARDF Championships.

2013 Team bronze medal in the 3.5 MHz competition in Poland, 19th World ARDF Championships.

2014 Team gold medal in the 144 MHz, team bronze medal in the 3.5 MHz competitions in Burabay (Kazakhstan), 17th World ARDF Championships.

2015  Construction of an Automatic ARDF Transmitter for Classic, Sprint and Fox-Oring events.

Winners from 1961 to 2012

Courtesy of Jan Hoek, PA0JNH
Table of results of ARDF IARU Championships


Andras SRJ