General Description for a Top Band DF, Multi Tx
Apr 2012)Printer friendly version is here.
1. The Principle
This style of radio direction finding uses relatively powerful transmitters (Txs) to lead
you to areas where less powerful Txs may be heard. The term parent is
used below to indicate this action.
2. Types of Transmitter
– manned, normal power, should be audible at the start; intended to
bring you to a site where other types of Tx may be found. A Maxi may
act as a parent to several Minis or Micros.
Mini Tx –
Lower power (range just over a Km), automatic Morse and timings.
Frequency 1.96 MHz (the allocated frequency for an unattended station).
A Mini may act as parent to a Micro.
– very low power (just over 200 metres) not requiring licence,
continuous ‘beeping’ signal
In the picture
Maxi A attracted competitors from the start location 20Km
Maxi A was 'parent' to Minis H, I, J, K, L and Micro Y.
Mini H was parent to Micro W
Mini J was parent to Micros X and Z.
site spread over three wooded areas with several different parking
places. The red dotted line shows one of the important
Once they arrived some competitors completed
the event on
foot, others used their cars to save some walking. The winner
67 at the time!
3. Transmission Times are based on a five minute
Tx transmits for the first minute of each cycle.
Transmissions may be extended as the event progresses.
Mini Txs will transmit in a sequence, each being on for one minute of
Micro Txs will be on continuously.
(Note - if two sites and two Maxis are used then then they will also be
synchronised - see the organisers information.)
4. Location and Distances
A Mini Tx will be less than 1Km from its parent Maxi Tx
A Micro Tx will be less than 200m from its parent which could be either
a Maxi or Mini Tx.
To avoid theft, Minis and Micro Txs will be extremely well hidden and
no attempt should be made to uncover them. It is the tickets that are
searched for, see below, these will be located within 3 metres of the
a Maxi Tx is located in a car or building then a green DF sticker
will be placed in the bottom left of a window. Do not trouble an
occupant unless you spot the sticker! (Note - this is rare, but may be used if the transmitter is particularly valuable).
This is achieved by numbered tickets located close to each transmitter.
When a competitor finds the tickets the highest value left is taken.
All tickets must be handed in at a Maxi Station before the end of the
competition. The winner is the person with the highest total score. In
the event of a tie, the person who has the most Maxi points wins. If a
competitor finds Minis or Micros but no Maxi and thus can’t hand in
tickets, they are ranked after all those who do find a Maxi.
Jokers are used to encourage individual searching and to provide some
help for beginners.
6. Tx Identification and Transmission Format
Each station is identified by a single letter. For legal reasons each
Maxi or Mini is also identified by the operator’s callsign sent in fast
Morse. Note that since an operator may have several Minis on his site,
using the operator’s callsign, it is of no value in the competition.
Listen for the slow single letter.
A sample transmission for station J, operator G4ABC is below (fast slow)
TEST DF J DE G4ABC/P J J carrier
until 30s J carrier
to 40s J carrier
to 50s J carrier
Txs may follow each other with no obvious gap. The fast Morse indicates
the start of a new transmission. Recordings of the Txs may heard here.
It will also be possible to identify a station by the time it is on
within the 5 minute cycle. An accurate watch is a big help!
7. The Object of an Event
The winner is the person with the highest total score. However, the
tickets show which stations have been found, so event organisers can
set up some easy stations and offer other prizes to encourage beginners
and the less physically adventurous.
you are considering coming along to a event check out the greater
detail provided by each of these links: