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There are different frequency bands to work with in radio tracking.
Nowadays, there are receivers build in different frequency bands, which will let us cover the channels’ range that we were more interested in to carry out our animal tracking.
Apart from technical considerations regarding each frequency band (such as: sensitivity, radio-electric background noise, ease of obstacle penetration or interferences), we should know which is the frequency allocated to radio-tracking in each country. For instance, the current allocated frequencies to radio-tracking in the European zone are in the UHF band (433/434 MHz). In the same way, there are other countries where the allocated frequencies are in the VHF band (216 MHz/173 MHz/150 MHz). So, the frequency band that we will choose will depend on the current legislation of the country where we want to work with our radio-tracking equipment.
The range at VHF is, theoretically, superior to that at UHF due to better penetration of the flora. However, we should clarify that into practice, and because of the electrical noise which exists at the VHF band (much higher than the one at UHF), we often get better range at UHF if we are well placed.
-Background noise and interferences:
Trees and small obstacles between emitter and receiver produce a signal fading. The background noise existing at VHF can jam signals if the obstacles cause an excessive signal fading. If the signal is not above the background noise, we will not be able to distinguish the transmitter pulsing signal from the background noise and the signal reception will become impossible. This doesn’t happen at UHF because the background noise is much weaker at this frequency band. As a result, in many occasions we will get better range at UHF than at VHF. The interferences proceeding from industrial machinery, high tension lines, etc. will also avoid the proper reception of weak signals. This effect is importantly reduced when working at UHF.
At VHF, antennae are large and bulky (around 80 cm). On the other hand, at UHF these are small and easy-to-use (35 cm approximately). This fact allows us to use them really easily and with much more agility when we are tracking an animal.
The use of VHF antennae, or lower frequencies, can remarkably difficult the activity especially in closed areas with lush vegetation.
When while we are searching we find different signals in different directions, we have to know which one is the correct signal and which signal is a rebound to start the research in the correct direction. In cases like this, we can use the digital tone processor (PT-3). This device is especially designed to distinguish between direct signals and rebounds. The PT-3 will let us know the correct direction to follow so we can reach the animal with no losses or unnecessary wasting of time.
This device is placed inside our more advanced telemetry receivers and it can process digitally the received signals. The PT-3 takes a received signal, processes it and creates a new signal. As a result, we obtain a clean, strong and longer sound, even if the received signal was weak and with a lot of background noise.
The utilization of this device allows us to differentiate between direct signals and reflected signals since the last are much weaker. Those little differences that are perceived neither by the hearing sense nor by the pointer are detected by the digital tone processor (PT-3), and it turns them into great acoustic and visual differences which can be easily distinguished.
Due to its great precision, the reception angle lessens in a considerable way. So, we can get a better precision when determining the direction of the obtained signal. PT-3 allows us to find the place where an animal is hidden with almost perfect exactitude, just with a few centimeters error.
When the batteries are not correctly used, you can get upset with the emitter’s performance.
Practical advice for a correct battery handling:
• Don’t keep batteries with other metallic objects since they can short-circuit causing a loss of their charge and, consequently, their autonomy.
• Don’t protect batteries with adhesive tape as there could be rests of glue which will difficult the current transmission when you want to use them.
• Do use always the supplied plastic sheath so the external perimeter of the battery remain protected of electric short-circuits which can be produced through the emitter’s battery compartment. In case that you use a tube emitter, you will also have to place this protection because, otherwise, the emitter can remain switched on even if the cap is not screwed in (since there is contact between the battery and the tube’s wall).
• When you place two or more batteries in the insulating sheath, you must be very careful to avoid them to be crossed.
• The collocation position of the transmitter’s batteries is the one indicated by the manufacturer. It is specified on the corresponding user’s guide for each transmitter.
It normally consists on placing the negative pole of the first battery contacting to the battery’s compartment centre and the positive pole (which corresponds to the body) touching the negative pole of the next battery. This type of assembly is known as “connection in series” and it is useful to add up batteries’ voltages.
Nevertheless, sometimes it is different. For instance, the hunting dogs’ emitter has the negative pole on the cap.
Conventional battery testers are not very helpful to test transmitter’s batteries. The reason is the following: these testers don’t show the battery’s charge rate that is remaining; they only give us the battery’s voltage.
Despite the existence of much more elaborated testing system, these are too complex to use and, generally, not easy to access. In case that, and spite of this, if you want to use these systems, you should consider that the battery mustn’t bee connected to the tester for a long time as a partial discharge is produced every time that it is tested. Otherwise, if you use a group of batteries, remember to test them separately.
It is defined as the receiver’s ability to pick up a signal input with the widest relationship with the Minimum Detectable Signal, until a maximum signal without reaching saturation. This relationship is measured in dB. A good receiver must have a dynamic range of, at least, 100 dB. When this value is not high enough, the receiver becomes saturated and, when it is placed near to the emitter, it receives signals from all directions or in a very wide angle. When the animal is hidden between weeds or bushes, we will need a very high precision.
This defect is typical from many old receivers that, in some cases, use an additional attenuator -activated by a switch- which lightly improves this behavior. A modern receiver must be capable to receive powerful emissions of a range of distance from 50 km to a few centimeters without reaching saturation and with no need of an additional attenuator for short distances.
The digital tone processor permits to introduce one or various improvements on the signal reception as well as on its reproduction, improving even the receiver’s sensitivity or the signal’s quality. We have backed the last improvement; with our PT-3 system, we get clean, strong and long signals even though the emitter is a long distance away from the receiver. We also achieve an extraordinary precision improvement, as the reception angle decreases, which only causes a very few centimeters errors.
The background noise at VHF is much more important when we place the antenna vertically. It is because most of the interference sources radiate vertically and, unfortunately, it is often the best position to receive a transmitter signal with the maximum strength. So, frequently, it is advisable to place the receiver’s antenna in a position neither vertical nor horizontal in order to lessen, as much as possible, the background noise with the minimum loss of useful signal.
It has happen that an animal has hidden itself in a big city carrying a VHF transmitter and it has been so difficult to track and find this animal because of the interferences. In these cases, it is advisable to check a searching technique called back-interference method. (How can I avoid interferences?).
When a fast animal, such as a bird of prey, chases a target, it can fly extremely quickly and, if we are not properly located (in a high place with good visibility), we could not receive the signal in the best condition. This fact might cause a misunderstanding and we may walk toward the opposite direction. If this happen, we should look for the highest position even if we go away a little bit. Signals may be very weak and the background sound measured in different situations and places is from 10 to 400 times the minimum signal that a receiver picks up at VHF -what means that the signal will not be properly received. This problem is less important at UHF.
Triangulation in radio-tracking is a technique with which we look for different reception lines (from a same transmitter) that converge in a specific geographic point. When we are searching a falcon or using radio-tracking for any other application which places the transmitters many kilometers away from the receiver, it is advisable to look for the emitter’s signal with the directional antenna. This makes possible to establish a direction on the terrain’s cartography. We should draw a line on a map (this line can be real or just imaginary) which represents the signal’s trajectory. It would be better if we take some measurements from different and separate points. All this procedure will make possible to determine the position of our transmitter since the trajectory lines will converge. This intersection will show us our emitter’s position. We will get better results if we have a 90 degrees angle formed by two of our trajectory lines. These measurements can be repeated as many times as needed.
We define top-quality conditions for transmitting as the situation where the emitter and the receiver are in open and treeless field, in a high enough position and without obstacles between them.
The emitter should be located in a high place, like a hill or a mountain. We should not place the transmitter on the floor but at 2-4 meters high. To lift it, we can hang the transmitter on a tree or raise it up with a wood stick. It would be advisable to have the emitter in open and treeless field, with no buildings around.
The receiver should be located in a high place like a hill or a mountain, as well. We will position the antenna to face the emitter, trying to find the maximum reception signal.
We will adjust the receiver to get the maximum gain; with the gain control at 10 and the fine tuning control where we got a maximum auditory signal and the maximum intensity, as well. It would be advisable to have the receiver in open and treeless field, with no buildings around.
We can fasten a transmitter to the bird’s tail by means of two main elements: the tail spring (attached to the emitter) and the tail-mount piece, where the tail spring is inserted. The tail-mount piece must be attached to the bird’s central feather, this union can be reinforced by some instant glue (non water-soluble). The spring gets into the mount piece so easily but it cannot fall out since the spring’s points are folded. To take out the spring, we should press both spring’s arms until they get together and extract it from the tail-mount piece.
This kind of fastening consists of “hanging” the emitter on the bird’s leg. By means of a leather strip, we will attach the transmitter (using the cap with a little hole) to the bird’s leg. This type of fastening is very practical but not very advisable since the transmitter will be knocking on each surface where the bird stops. All this, may considerably damage the transmitter’s electronic circuit.
With this system, when the animal is standing on the ground, the emitter’s radiation is very limited because the antenna touches the ground. This is particularly important when the ground is wet.
The harness fastening consists of the attachment of the emitter to the bird’s back.
We need a harness kit (a harness mount and a teflon strip) and a tail spring. We will fasten the harness mount to the back of the bird by means of the teflon strip. The harness collocation might be a bit difficult if our bird is a little nervous. Once we had the harness on the bird, we should insert the tail spring (attached to the emitter) into the harness mount hole.
This is the most suitable fastening system as it offers a better performance and protection to both transmitter and bird.