Norfolk Amateur Radio Club

DF100 direction finder project for “Foxhunting”

The DF100 is a simple direction finder designed for ‘Fox Hunt’ events on 2 metres, although could

be adapted for other bands. Basically it works by using 2 identical Dipoles parallel with each other and

alternately switched so that the signal picked up by each can be heard alternately by the receiver. As

the Dipole is rotated there comes a point in which the signal reaching both dipoles is exactly the same

and in this way the direction can be ascertained. Although simple in design the circuit is remarkably

effective, the only real flaw being that the signal direction could be either in front or behind the

dipole! By using a reflector (even your body!) and a careful ear the real direction can be discovered

and there is plenty of scope for experimentation in this and other aspects of the design. For more

information on Fox hunting/DF equipment check out the web - there's plenty there!

We hope this NARC kit with encourage members to venture both into some construction work and

also take part in the fun event that is fox hunting - it does not have to be just a once a year event!

Making it easy......

A NARC club kit of the all electronic parts, including PCB, is available as a service to club members -

the other materials required to make the Dipole etc are readily available DIY materials you will probably

already have at home. The kit of parts is entirely optional - you can just have all the information if you

want to make it entirely yourself, including PCB artwork (although it should also work on veroboard).

What the NARC kit contains:

1 x NE555 Timer

1 x IC socket

1 x 1K resistor

1 x 100K resistor

4 x 470R resistor

2 x 10nF capacitors

3 x 1nF capacitors

2 x 1N916 equiv diodes

1 x 2 Pole 3 position centre off toggle switch

1 x PP3 Battery clip

1 x DF100 PCB (needs to be drilled)

1 x BNC plug prewired to long length of RG58 50

Ω coax (connection to receiver)

Coax cable to link Dipoles to PCB - these are made from the ample

Cost for kit of parts as above £5

What you need to provide:

Handheld or other portable 2M radio receiver or transceiver

1 x Tobacco tin or similar (Mustard?) for case (must be metal for screening)

4 x Lengths of stiff wire for Dipoles (eg wire coat hanger)

Wood for mounting Dipoles

Wood screws

Small pieces of scrap copper clad PCB for Dipole connections

General information

Whilst the club is able to loan basic hand and soldering tools we ask members to bring as much of

their own equipment as possible so that those without tools can take part. We have permission to do

basic electronic assembly at the club QTH but ‘hardware’ work like drilling and wood cutting must be

done at home.

DF100 Direction finder concept and design by Doug G3HUL

Engineering and club project coordinator David Palmer G7URP

Home 01953 457322 / Office 01953 458844 / eMail dpalmer@dcpmicro.com

Version 1.2 26.5.03 (coax braids reversed)

Publication © David Palmer G7URP

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