ARDF transmitters

For 2m and 80m including controller/timer

Thanks to the great work of Rik ON7YD, Jacques VE2EMM, Francois VE2JX and Leo PA0LEZ I have been able to assemble some of their fine designs and put a bit of my own into a project for making a complete set of 2 and 80m ARDF transmitters and fox controller/timer.

So many credits go to the designers. All of this was done without commercial interest and only for radioamateurs.

(by Edwin PE5EDW, and read the disclaimer on the bottom of this page....hi)

2m transmitter and fox controler/timer

(Source: ATX2 designed by ON7YD and MFC3 and software designed by VE2EMM/VE2JX)

The 2m ARDF transmitter that was selected for this project is the ATX2 and is partially used, because there was no need for an on board tone generator (and the pcb trace was cut at the modulation input). However the tone gen components can still be put in place and are made optional. The modulation tone is generated by the ARDF timer itself and directly fed into the modulator in the collector line of the RF output stage. Another modification was to incorporate a series resonance circuit connecting the output of the ICS501 to the base of the RF output transistor (this IC delivers about 40mW with 26 Ohms Z out). This was done to filter out unwanted harmonics generated by the ICS501 and only keep the 2m signal. The transmitter runs on 12VDC and generates about 350mW of RF power (depending on which transistor is used. (It seems that the 2N3866 delivers the most RF power).

The newer schematic has a BLT50 smd transistor that needs about 10V power supply and outputs about 800mW. So less batteries needed and more power. The BLT50 fit without modification to the PCB on the copper side of the ATX2 print.

The ATX2 was married to an MFC3 (Montreal Fox Controller v3). The software that drives the PIC16F84A was modified by PE5EDW in order to get more options, like switchable 30 sec./ 60 sec. fox transmission duration, which is currently popular in the Ukraine and gives a healthy boost to those who want to go even faster in the course. Because of this I had no room anymore for the external programming of the hider's callsign (this is now hardcoded in the software, but easily changed and re-written to the PIC's).

The schematic is of course available, but is only a copy of what was already made by ON7YD and VE2EMM/VE2JX, somewhat modified and put in sPlan 6.0. The PCB for this transmitter/timer combination is made in Sprint Layout 5.0.

The whole setup was put on a pcb strip of 160 x 35 mm, making it suitable to be put in a pipe of about 50mm diameter. It has been design so that if necessary the timer can be separated of the ATX2 section. (Thought it might be usefull).

Click for full size PCB
MFC3 and ATX2 married on one pcb (160 x 35mm)

The software for the timer was written in C by VE2EMM and VE2JX and modified by me to host a number of changes that I find myself particularly nice to have (hi). See the listing below for all software modifications (it reflects the "type 4" software that is currently my preferred version). I made several version with incremental updates and modifications. You can download the type 4 C-code and hex files that I prepared with "ARDF" as the hider's callsign (can be changed on request), just browse through the C-code for fun ;-)

The original software can be found on VE2EMM's website.

------ FOXHUNT TIMER / Montreal fox controller 3 / Type 4 (for PIC16F84A)

Auteur of original software: VE2EMM (Date: Jan 2003)
Modified by: PE5EDW for personal customizing (Date: Sep 2007)

1) steady key and tone after hiders callsign until end;
2) hardcoded PE5EDW in EEPROM, any callsign can be set on request;
3) translated and added info lines in English;
4) steady LED first sec during delay time on selected fox minute;
5) no intermittent LED during delay time;
6) MO has only call_id and no TX OFF between minutes;
7) normal cw speed 8 WPM (IARU ARDF rules Part B, rev.1);
8) interval set to 5 sec to compensate for 8 WPM;
9) delay time 0/0.5/1/1.5/2/3/4/6 hrs. selectable (dip sw. 0..7);
10) multiple hiders callsigns in remarks;
11) added 30 sec. cycle when RA3 is low else 60 sec. cycle;
12) only call_id's when 2,5 min. mode is selected, no steady key;
13) in 2,5 min. cycle MOE starts with hider's callsign;
14) Exchanged 16F84.h file by 16F84A.h for suitability (no impact).

80m transmitter

(Source: 80m transmitter is designed by PA0LEZ)

The somewhat unusual design of this high power 80m transmitter incorporates two BS170 N-channel FET running in parallel having their own gates driven by a separate NAND gate buffers (HEF4011BP). The same IC also generates the 80m RF signal and switches the RF output on and off. The power to the HEF4011BP is removed when the fox controller/timer is in TX OFF state by a FET switch with a BS250 (P-Channel).

The oscillator/driver with the HEF4011BP was originally used as FoxOring transmitter. The early design of this 80m transmitter contained a TTL IC and had to be run from a 5VDC source. I have replaced it by the CMOS IC to make it run on 12VDC. The transformer was originally 1:2, but has been set back to 1:1 with this higher power supply voltage configuration.

The pcb contains space for a antenna tuning coil, but can be replaced by a jumper when an external antenne base loadingcoil is used. The tuning is done in the earth lead going to the radials or earth pin.

The circuit design matches with the fox controller/timer circuits on the 2m board, so they can be put in on housing to make a dual band ARDF transmitter set with one controller. The 80m PCB is sized to 70 x 35mm.

The transmitter runs perfectly on 6 to 12 VDC and generates about 2W of RF power (but it can go even higher with these FETs, hi)

Click for full size PCB
80m fox transmitter (70 x 35mm)

The schematic shows also the tuner used in some field experiments and shows good performance. In the latest testruns an earth spike (pin of about 30cm) was used in stead of the usual radials. The signal was still very strong and stable. I have seen this being used also during the 13th ARDF World championships in Bulgaria in 2006, where they used a 50cm threaded iron rod of about 8mm diameter driven in the ground. And let me tell you, the foxes could be heard everywhere in the area with lots of hills and valleys.


I have prepared some documentation to go with the whole thing.

80m transmitter pcb layout and schematics

2m transmitter and controller/timer pcb layout and schematics


Print layout masks for photographical pcb production on request (email me).

HAVE FUN ! ! ! ! If you need more information, don't hesitate to contact me.


Edwin Verburg PE5EDW

Last update: 25-Aug-2010

Disclaimer: I will take no responsibility for any errors in the layouts, diagrams and/or design flaws that might lead to any kind of damage or financial loss. This is because of the "A" in HAM and the non-commercial nature of this project. So no guarantee, but remarks and suggestions for improval are happily received (hi).