Here is a fun exercise that has practical applications...
No Ham license needed
Amateur radio direction finding (ARDF, also known as radio orienteering, radio fox hunting and radiosport) is an amateur radio sport that combines radio direction finding with the map and compass skills of orienteering.
Fox hunting involves searching for a hidden radio transmitter using radio direction-finding equipment. The objective is to be the first to locate the hidden transmitter(s), often referred to as the "fox." The fox can be located anywhere within a designated area, such as a park, forest, or urban area.
The origins of fox hunting can be traced back to the early days of radio communication. Radio direction-finding was used in the early 1900s to locate ships in distress and to track down enemy radio transmissions during wars. In the 1920s, amateur radio enthusiasts started using the technique to find hidden transmitters, which led to the development of the sport of fox hunting.
Today, fox hunting is a popular activity among amateur radio operators, with competitions held around the world. On the international level, the sport requires a combination of technical skills and physical fitness, as participants need to be able to navigate through different terrains while using their radio direction-finding equipment to locate the hidden transmitter. Locally, it becomes a ‘walk in the park’ and doesn’t require a high level of physical fitness.
There are different types of fox hunts, each with its own set of rules and objectives. In some hunts, the fox transmitter is located in a fixed position and participants must find the transmitter's exact location using direction-finding equipment. In other hunts, the fox transmitter is mobile and participants must track its movements through a designated area. The fox transmitter typically emits a Morse code (CW) signal with dits indicating the ID of one of a series of foxes, thus making it easier to locate.
The gear
One of the key components of fox hunting is the radio direction-finding equipment. This typically consists of a directional antenna and a radio receiver. No license is required because you do not send any RF signals yourself. The receiver’s directional antenna is used to determine the heading to the fox transmitter, while the radio receiver is used to pick up the transmitter's audio signal. By rotating the antenna and listening to the signal strength, participants can determine the general direction of the fox transmitter.
ARDF events use radio frequencies on either the two-meter or eighty-meter amateur radio bands. These two bands were chosen because of their universal availability to amateur radio licensees in all countries. The radio equipment carried by competitors on a course must be capable of receiving the signal being transmitted by the five transmitters and useful for radio direction finding, including a radio receiver, attenuator, and directional antenna. Most equipment designs integrate all three components into one handheld device.
On the VHF two meter band (~144 MHz), the most common directional antennas used by competitors are two or three element Yagi antennas made from flexible steel tape [pictured top right]. This kind of antenna has a cardioid receiving pattern, which means that it has one peak direction where the received signal will be the strongest, and a null direction, 180° from the peak, in which the received signal will be the weakest.
On the eighty meter band, two common receiver design approaches are to use either a small loop antenna or an even smaller loop antenna wound around a ferrite rod [photos right].
These antennas have a bidirectional receiving pattern, with two peak directions 180° apart from one another and two null directions 180° apart from one another.
The peak directions are 90° offset from the null directions. A small vertical antenna element can be combined with the loop or ferrite rod antenna to change the receiving pattern to a cardioid shape, but the resulting null in the cardioid is not as sensitive as the nulls in the bidirectional receiving pattern. A switch is often used to allow the competitor to select the bidirectional or cardioid patterns at any moment.
This ARDF receiver equipment is designed to be lightweight and easy to operate while the competitor is in motion as well as rugged enough to withstand use in areas of thick vegetation.
ARDF is a sport that continues to evolve, with new technology and techniques emerging all the time. The future of the sport is likely to be shaped by advances in radio technology, including the use of software-defined radios and artificial intelligence. The sport is also likely to become more accessible and inclusive, with efforts underway to encourage more women and young people to participate.
In addition to being a fun and challenging sport, fox hunting also serves a practical purpose. Radio direction-finding is an important skill for emergency responders, search and rescue teams, and other organizations that need to locate people or objects in difficult terrain. By participating in fox hunting, amateur radio enthusiasts can develop and refine these skills, making them better equipped to assist in emergency situations.
On a local level, fox hunting is a rewarding sport that requires minimal training and average fitness. It's a great way to explore the outdoors while also honing your radio communication and direction-finding skills. The sport also provides an opportunity to connect with other ham radio enthusiasts and participate in a friendly competition.
What do you do when you find a fox?
Generally SARC puts out 5 foxes in a large park. Each has a Morse code signature of dits from 1 to 5 to identify it. There is a punch attached to each fox and you punch the corresponding fox number on your card to validate the find. When you have all 5 you return to the start point.
[below] Anton VE7SSD locates a fox and punches the card
SARC has a number of receivers for loan during the event, or you can tag along with an experienced hunter. At the end we have a barbecue to cap off the event.
If you're interested in trying out fox hunting, there are many resources available online to help you get started. You can find information on local clubs and events, as well as tips and tricks for improving your direction-finding skills. Surrey Amateur Radio Communications and many other ham radio organizations also offer training and events for fox hunting enthusiasts [see the poster below].
So grab your radio and head out into the outdoors for a great Amateur Radio family event – the foxes are waiting to be found!
Remember, all you need is a receiver, no ham license required.
SARC member Les Tocko VA7OM designed a top notch contest grade ARDF 80m receiver that is now available. Inquiries may be sent to VA7XB@myrac.ca. Les and Amel presented a SARC meeting program on ARDF and the receiver in April 2022, following up on a presentation first given on March 11, 2020, when the receiver was still in development. The development team included his cohorts Amel Krdzalic VA7KBA and Dave Miller VE7HR. He has shared his presentation slides and two videos. Here are some links:
A video on the use of the new receiver
~ John VE7TI
No comments:
Post a Comment