Direction Finding Rules

Start Time: 19.00BST for 19.30BST start.
Finish time: 21.00BST
Start Location: You may start from anywhere
Map Required: OS Landranger 173 Swindon & Devizes 1: 50 000.
Hunting Area: Anywhere on above map.

On completion of the event, the “Fox” will reveal the location of the Pub on the event transmit frequency. If any of the “Hounds” do not hear the pub location for some reason e.g. receiver failure, they can, in emergency, phone the “Fox” on 07810317750.

We would really appreciate you indicating before the event that you are taking part. This ensures we know when to end early.

Schedule of Rules

Part 1 “The fox”

  1. Transmit Frequency : 145.275 MHz (Unless notified during event or in event of QRM).
  2. Callsign : G8SRC/Mobile
  3. Location : On public or common land, or in sight of a public highway.
    At end of event, or when all “Hounds” concede or find the transmitter, the “Fox” will transmit the location of the pub and then close down.
  4. Transmissions: The “Fox” will transmit a vertically polarised signal. Each transmission will include a period of unmodulated carrier (F3N) and a period with a tone. Transmissions will be 10 minutes long.
  5. Transmit Schedule (Times BST) : 19.00 to 19.10; 19.15 to 19.25; 19.30 to 19.40; 19.45 to 19.55;20.00 to 20.10; 20.15 to 20.25; 20.30 to 20.40; 20.45 to 20.55

Part 2 “The Hounds”

Teams can be single or multi-operator.

Any communications between the “Hounds” must not be on the “Fox’s frequency” or close to it. Use S20 and then switch to another agreed frequency. The “Fox” will not respond to CQ’s.

At all times participants shall observe the Highway and Country Code and if licensed their licence conditions.

Suggested Equipment List

Receiver/Transceiver; DF antenna; attenuator; antenna switch; coaxial cable; coaxial adapters/connectors; pole/mast (non-metallic); OS map; tracing paper/ acetate as map overlay; pencils/pens; board for map mounting; straight-edge; compass; fuel in tank.
Points To Remember

A dual band rig can be useful, as it can be used to take bearings on the 3rd harmonic of the “Fox” frequency, when working close in. Try building a “sniffer” – a 145MHz crystal set with DC amplifier and meter, this is an insensitive RX, that copes well in strong RF fields. Try to shield the RX from strong RF fields. Watch out for local phasing/reflections caused by buildings, hedges, hills, cables, car bodies, etc giving rise to anomalous S meter readings. When taking bearings, walk a few meters from the first and then take another, this may help to average out the anomalies. Try to take bearings at 90 degrees to the previous. Make a mental note of S meter readings on your reference antenna – e.g. your mobile whip. Before the event, study the area for suitable points from which to take bearings.

Remember to subtract approximately 5 degrees from your compass bearing, prior to plotting your beam heading. If you can, reference your beam heading to a landmark or feature, which can be identified on the OS map.

Deryck G3YKC

(The above DF contest information is based upon that used by the Trowbridge & District Amateur Radio Club)