Retro. To the day of Radio - "Fox Hunting", 1957

Very soon (tomorrow, May 7th) is Radio Day.

Maybe someone saw a fragment of the competition - when participants run around the forest with some kind of radio receivers, and did not really understand what the matter was, and what did they lose? This competition is called “Fox Hunting” (“Catching Foxes”) - officially called “Sport Radio Direction Finding”. And its essence lies in finding the source of the radio signal in an open area.
')
Radio magazine, back in 1957, was the first detailed publication devoted to this competition in the Soviet Union, this post will be a digitized version of this article, which tells all the details of this action (the publication was agreed with the editors of Radio magazine).

This summer [1957] the 6th World Festival of Youth and Students for Peace and Friendship will be held in Moscow. Thousands of friendly meetings between the young representatives of various nations will occur these days in the capital. Here will meet students, workers, athletes, teachers, sailors. In Moscow, radio amateurs of many countries of the world will gather together. They will exchange views on strengthening friendship ties, talk with their friends over the air, and meet at friendly competitions.

The program of the festival, among other sporting events, includes the ultrashort-wave competition “Catching Foxes”. This type of VHF sports has become widespread in several countries around the world. He is also of great interest to our youth. This year's competition "Fox Fishing" will be held in many cities of our country. They will select the best athletes who will join the team of radio amateurs - participants of the festival. How is Catching Foxes organized and conducted in Yugoslavia?

We addressed this question through the editorial office of the magazine Yugoslav radio amateurs Radiomater to the winner of the 1956 competition in Belgrade Zhenko Zdravko. Below we publish, with some abbreviations, the article kindly sent to them.

Competitions radio amateurs, called "Catching Fox", are perhaps the most interesting and exciting. This new type of VHF radio began to spread among radio amateurs only a few years ago, but it has already gained wide popularity.

In the Federal People's Republic of Yugoslavia, such competitions were first held at the 1st meeting of radio amateurs in Ljubljana in 1954, after which they began to organize regularly.

What is the meaning of this competition? The participants are given the task: as soon as possible to find a radio station that is pre-installed in a place not known to them. After a certain time, say, every five or less minutes, the hidden radio station - “fox” - sends its call signs on the air for 30 seconds to a minute. Taking them, the participants of this kind of hunt determine which direction they should move.

The distance between the "hunters" and "fox" depending on the area can be different - from 2 to 7 km. Consequently, the “hunters” need to have portable battery receivers and special antennas with the maximum directivity of action. It is desirable that they have a watch. This will relieve them from the need to continuously listen to call signs and they will be able to pay more attention to the terrain review.

A compass and a map can also be of great help in “hunting”, although they take a lot of time. Sometimes the competition regulations stipulate that the “hunter” must map the points where he took each of the fox's call signs, the direction from which the radio station’s signals were heard, and the route of his movement. Cards should be all the same, in good performance, with all the details. The organizing committee distributes them on the eve of the start, so that participants have time to get to know them.

In the immediate vicinity of the hidden radio station, “hunting” becomes the most difficult and at the same time exciting, especially if there are several “hunters” in front of the target. Everyone wants to win first place, and the "Fox" is silent until the next series of callsigns.

It is quite clear that the more ultra short-haired radio amateurs will take part in Fox Catch, the more interesting the wrestling will be.

When organizing competitions, it is necessary to pay particular attention to the strictest secrecy when choosing a place for the "Fox". Best of all, the team that is entrusted with the maintenance of this radio station, on the eve of the competition itself chose a place. No one should know where she disappeared. Transmitter "Fox" should run on batteries. This will place it anywhere.

The Fox team consists of two or three operators to service the transmitter and register the hunters-winners. Members of this team are also obliged to take care of hiding the “hunters” who are the first to find the “fox”, otherwise with their presence they can discover the whereabouts of the “fox” to the other contestants.

Call signs "foxes", regardless of how far from the radio station are the "hunters", should appear on the air at precisely set intervals. It is necessary that the transmitter power remains constant all the time. It is also undesirable to change the direction of the antenna. If possible, the polarization of the antenna should be horizontal. The duties of the special commission include a thorough check of the serviceability of the receivers of the “hunters”, especially at the finish.

The start of the "hunters", as already mentioned, is given at a distance of 2 to 7 km from the "Fox". Immediately release a large group of "hunters" is impractical because they will interfere with each other in the reception. In addition, the possibility is not excluded that there will be those who, without hearing the “fox”, simply follow in the wake of a more experienced comrade. Most often they organize one or two starts, located close to each other, and release “hunters” at five-minute intervals. "Hunter" is allowed to turn on the receiver only at the time of launch. The rest of the competitors do not have to see in which direction the starters go.

Special difficulties are created by “hunters” reflecting the “fox” wave from mountains, large buildings and other obstacles. It often happens, for example. that the “hunter” is moving in a completely opposite direction and when he reaches the “finish”, he is suddenly convinced that the “fox” is exactly where he has just come from. Thus, you can wander for a very long time, until you finally guess to step aside and explore the area.

A similar story happened to me in competitions in Belgrade. I climbed one elevation, and when I reached its summit, I became convinced that I had to go back down almost in the same direction.

Or an example. During the local competition in Ljubljana, my friend was searching for an “fox” in the bushes near a small grove for an hour, as his antenna, no matter which side he approached, always pointed at the grove. In the end, we began to worry about him, called him on the radio and advised him to go behind his shadow. He had a bewildered look when he came out of a grove 400 meters away from the real target.

But not only the forest gives "hunters" a lot of worries. It is also necessary to beware of large metal structures, telegraph lines, railroad tracks, as they are capable of reflecting and deflecting waves.

Competitors should pay close attention to all this. In addition to hearing, the “hunter” must also mobilize his eyesight in order to notice and take into account possible obstacles in time. In order not to stray from the right direction, it is recommended to outline a landmark - a tall tree, a building, etc. Having taken the next series of callsigns, the “hunter” checks whether he has not deviated from the main direction. If a significant deviation is still far from the “fox”, then the “hunter” is dealing with a reflection. Here you need to be especially attentive. When there are no major obstacles that could reflect the waves, it is best to continue on the way in the middle direction. Thus, the minimum of time is lost, and even if the “fox” is very close, all the same, it will not leave, since the “hunter” is approaching it in a spiral.

A “hunter” can have one assistant who carries a piece of equipment, if it is too bulky and heavy, maps a route, etc.

The practice of holding the Fox Fishing competition may be different. In a number of countries, motorized “hunting” is most often arranged. Of course, to do this, select the appropriate terrain. In Switzerland, competitions were held in boats on the lake: the “fox” moved among other boats that had nothing to do with the competitions. A completely new way of “hunting” was invented in Germany. "Fox" moves on the territory with a radius of 10 km. It is monitored by four special stations with goniometer-type antennas, which guide the “hunters” on the fox tracks. All competitors move on motor vehicles.

But, in my opinion, “hunting” on foot is more enjoyable, especially if the weather is good, the terrain is crossed, unfamiliar, and there are frequent reflections of the waves.

Briefly about the technical equipment "Fox". Its transmitter does not have to have much power, since it works for a short distance. An antenna can serve as a normal dipole, but a two-four-element directional antenna is more reliable. If you use a powerful transmitter, then you can use a simpler antenna, which is easier to mask.

For the "Fox" especially "tricky" can be offered, a powerful transmitter with a fairly narrow antenna pattern. The antenna focuses on an object that gives a strong reflection of the emitted signals. Such a "fox" is great to confuse the "hunters" and makes the competition especially difficult and interesting. Installing false reflector antennas makes it more difficult to search for the “fox”, especially if the antennas are clearly visible, but are located in hard-to-reach places.

Of course, it is desirable to have a transmitter with good frequency stabilization. We, for example, in the largest competitions used transmitters with quartz stabilization. This was necessary because two “foxes” were caught at once, working alternately on the same frequency. Such competitions were held during the 3rd Meeting in Belgrade.

As a transmitter, you can use the transceiver of portable stations that are used by "hunters". In this case, the receiver must be turned off so that its local oscillator does not facilitate the search for "Fox".

I have already said that in order to facilitate the movement of the “hunter” his receiver should be portable and lightweight. To power it easier and more convenient to use dry batteries. However, the main disadvantage of this method of power is its high cost, especially if the radio amateur is not able to use the battery completely after the competition. There is a way more economical, but it requires a large initial cost. In this case, the alkaline battery of a small capacity is fed by the heat of the lamps, and the anode voltage is obtained from the vibrator.

If the radio amateur can not get the factory synchronous vibrator, then he can easily make the simplest asynchronous vibrator using the contacts of a relay and a homemade bias coil. Rectifier can be assembled on selenium columns or germanium diodes.

Building a receiver only for hunting fox is inappropriate. For VHF with a small complication of the scheme, you can build a transceiver, which can always be used for communication.

The receiver must contain no more than four lamps powered by batteries. The most suitable for this purpose is a conventional superregenerator. There are several regenerative receiver circuits. The simplest and cheapest is the receiver, in which the functions of the detector and the regenerator are combined in one lamp, the so-called superregenerative detector. There are receivers in which there is a separate ultrasonic frequency generator and a kind of mixer. Setting up such a receiver is difficult, but it does not give a significant gain.

The superregenerative receiver must contain a high-frequency amplifier so that it does not radiate into the antenna and does not interfere with the “hunt” comrades. Best results can be obtained by making a simple super-heterodyne receiver, which, with the same sensitivity, has the best selectivity and does not interfere with neighboring receivers. Making a superheterodyne receiver is available to a more experienced amateur, since setting it up is much more complicated and it contains a large amount of detail.

The use of VHF in competitions will provide an opportunity to use a small directional antenna. In the simplest case, for a “hunter,” as well as for a “fox,” it can be a normal dipole, whose radiation pattern looks like an eight. Such a radiation pattern makes it impossible to determine the direction to the transmitter, since the reception is equally strong in two directions. You can get rid of this disadvantage if you put a reflector behind the dipole. In this case, the reception becomes unidirectional. Even better sensitivity and directivity are achieved with multi element antennas. It makes no sense to install more than seven elements, since too strong antenna directivity allows receiving weak reflected signals, which confuses the “hunter”.

Aluminum can serve as a material for the antenna; it considerably reduces the price and simplifies the antenna, the latter is especially important if you consider that the antenna must be carried by one person. The three-five-element antenna of aluminum weighs no more than 600 g. The antenna can be made of thin wire. It should only be taken into account that the thicker the rods from which the antenna is made, the shorter the elements must be, since the thicker the antenna is, the greater its inductance.

As a feeder, it is convenient to use a symmetrical 300-ohm cable, but it is possible to use another wire, although a slight inclusion error can, however, degrade the reception quality.

Tuning the antenna requires a lot of attention. Precise frequency tuning and good matching with the input impedance of the cable ensure maximum antenna efficiency.

All experiments on the tuning of antennas are best carried out on the ground in such a position as it is supposed to be used later in competitions. In no case can you adjust the room, you can not lean the antenna against the wall, etc. It must always be remembered that the antenna is a kind of amplifier and, when dealing with low-power transmitters and simple receivers, we cannot neglect any trifle that may seem at first glance.

Zhenko Zdravko

A source

Story

The history of the appearance of this sport is described in sufficient detail here .

It all started with an article in the popular magazine Wireless World, dated July 21, 1926. This article was called "Tracking a concealed transmitter (Shefield Society's exciting field day):



The first mention of this competition in the USSR occurred in the magazine “Radio Amateur” in 1928, here is a scan of this page , entitled “Radio Hunting” (scan courtesy of the editors of Radio Magazine).

Modern fox hunting

The current state of “Fox Hunting” can be seen in this documentary (by the way, quite an intriguing beginning)