RDF Handbook V3 by VE3RDD

a very big thanks to Al Duncan Ve3RRD for sharing


Radio Direction Finding
Al Duncan – VE3RRD

v3 – March 2012
Radio direction finding or RDF has been around since before World War One. From the time of the invention of radio, there has been a desire to know from what direction a radio signal was arriving at the listener’s radio receiving antenna.
Amateur Radio has found several uses for RDF:

Hunting down interfering radio signals, both accidental and malicious interference to repeaters (affecting both ham and commercial communications, including emergency services).

Helping to locate downed aircraft by DFing their emergency locator beacons (ELT).

The entertaining sport of “fox”, “bunny” or T-hunting.
It is “fox hunting” that has spread through many ham radio clubs around the world as a very exciting and fun aspect of the hobby. Fox hunting can take many forms of transmitter hunting, from a person hiding within a few blocks of the starting point with his handheld and periodically making a transmission while others try to find him on foot using directional antennas; to a competition with multiple unmanned automatic transmitters scattered over a course that can be several hundred kilometers long – the entrants being required to find each transmitter in proper order with a minimum number of kilometers driven. Another variation called ARDF or radio orienteering is popular in Europe (just gaining popularity in North America) and includes jogging or running from one low power hidden transmitter to another while carrying RDF equipment in a timed race.
What makes fox hunting so popular?

The social aspect of getting together with others with similar interests.

Anyone can take part – you don’t need a ham license since only a receiver is required.

The satisfaction of building your own equipment such as an antenna or attenuator for use in RDFing.

The fun and competitiveness of the hunt, which also can involve both physical and mental exercise (walking while searching, and the calculations and map plotting required to determine where the fox may be located).

The outdoor aspect of the sport (sunshine and fresh air).

After the fun of the hunt, there is always coffee and conversation at Tim Hortons to look forward to.
The “fox” has several basic requirements:

Be able to move to a location unobserved by those who plan on taking part in the hunt.

Be able to hide well enough at the location he has chosen so he will not be accidentally spotted. The hunters should have to almost stumble over him in order to find him.

Be equipped with enough handheld battery capacity, water, lunch etc. for the expected duration of the hunt – it could be one or two hours or more in length, depending on the distance the fox is from the starting point and how well he is able to confuse the hunters as to his probable location.

Pleas download the complete book



One comment

  1. Mike Hohmann · March 23, 2017

    Well done, John. The reference material is appreciated. 73 de Mike, KEØGZT


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