- What you should know before buying a telemetry system!
When choosing a receiver you must take into account two important aspects: Sensitivity & Dynamic Range
Sensitivity
This is the ability of the receiver to get the faintest /weaker signals. As regards telemetry receivers it is
defined as the "Minimum Discernible Signal" and it is stated in dBm or microvolts.
The sensitivities are within the range
-130 dBm to -150 dBm (-130 dBm = 0'071µV; -150 dBm = 0'007µV)
Since they are negative figures, the higher is the dBm figure the higher is the sensitivity. In the 216 Mhz
band higher sensitivities can be obtained than in the 430 Mhz one.
130 dBm is the minimum sensitivity used in compact, handy receivers. If we use a receiver with a sensitivity
of -140 dBm, it is as though we had a transmitter ten times as powerful as in the first instance. With a
sensitivity of -143 dBm, it is as though the same transmitter were twenty times as powerful as in the latter
instance. When the transmitter is consuming the maximum energy from its batteries (which is likely to happen with the most powerful falconry and pidgeon-breeding transmitters) it is utterly impossible to obtain powers (caacities) ten to twenty times as high because the batteries cannot yield more energy. The only solution is to get more range by increasing the receiver sensitivity and/or processing the signal.
List of sensitivities:
-140 dBm. 10x as sensitive as -130 dBm (which is tantamount to multiplying the transmitter power by 10)
-143 dBm. 20x as sensitive as -130 dBm (which is tantamount to multiplying the transmitter power by 20)
-146 dBm. 40x as sensitive as -130 dBm (which is tantamount to multiplying the transmitter power by 40)
-149 dBm. 80x as sensitive as -130 dBm (which is tantamount to multiplying the transmitter power by 80)
Dynamic range
The dynamic range of a receiver is defined as the proportion between its "MDS" and the maximum signal it can receive without any distortion. This proportion is measured in dB. A good receiver must have a minimum d.r. of 100 dB. When this rate is not high enough the receiver gets saturated when it is a few metres from the transmitter, getting the signal either from all directions or from too wide an angle. But when the animal is hidden amidst the vegetation much more precision is required. This is a common defect with most old receivers, which sometimes have recourse to an additional (damper, silencer, dimmer, muffler) which can be started by a switch and relatively improves their performance.
A modern receiver must be able to receive powerful 50km-range transmitters from a distance of just a few
centimetres without either getting saturated or having to have recourse to additional dampers for close
distances. The VOL-GAIN control must be of the 'fine multi-turn adjust' type in order to get the best adjust
from the pointer, so that neither the receiver gets saturated nor the signal lost at the slightest turn from the control, as is the case with the conventional 310¡, single-turn controls. A receiver with such a low sensitivity as -130 dBm is more sensitive to get very close to the transmitter without getting saturated, since it doesn't amplify the signal so much, while it has a lower range.
- Our Famous Signal processing PT-3. The signal processing means several improvements both in the receiving and the reproducing of the signal, making it possible to increase its sensitivity and/or its quality. We have worked this out. With our PT-3 system we can get distinct, loud and long, even if the transmitter is many kilometers away. We can as well greatly improve precision by reducing the receiving angle which allows us a margin for error of very few centimeters.
This device, placed within our most advanced telemetry receivers, provides us with the following advantages:
1.- A three position switch .
- Low position: PT-3 is off. Only conventional system works.
- Middle position: PT-3 is on, as well as the conventional system.
- High position: PT-3 is on, as well as the conventional system and the light of the meter blinks at the rate of the received signal, to make night tracking easier.
2.- New signals are regenerated and produced out from the received signals. Thus the sound comes out louder, clearer and much longer, even from noisy signals.
The typical sensitivity of this system is 130 dBm.
3.- The reception angle can be greatly reduced up to the PT-3 performance limit, which can be reached by lowering the GAIN/VOL control.
4.- By using this device we can discriminate direct signals from reflected ones, because the latter are weaker than the former. Tiny differences which are imperceptible by the ear or even the pointer, will be etected by the PT-3 and thus transformed in large acoustic and visual differences, for a better appreciation.
Should we have to know where our bird is hiding, PT-3 enables us to find it with an error of just a few centimetres. PT-3 is also very helpful in order to discern whether the bird is getting closer or away from us
Learn How To Use The Signal Tone Processor PT3.
Smaller angle = higher precision
By using a receiver with a PT3 the angle is considerabluy reduced, so that we can better precise where the transmitter is.
Rebounds will no longer deceive us !
PT-3 enables you to precisely establish the actual direction the emitting signal comes from when it is apparently received from several directions.
A few inches forth and again back
We can precise determine whether the transmitter is getting closer or away from us by moving the receiver just a few inches to and away from the transmitter
- Finally, the truth about batteries!
Don't keep the batteries along with other metallic objects, because they will short-circuit and eventually
loose life-time.
- Don't preserve them with adhesive tape, because it can form an insulating coat that prevents the current from passing through them.
- Instead, a soft plastic pipe must be used, which is included with the transmitter. The batteries must placed in it in order for their outer perimeter to be preserved from electrical crossings. If just one battery is needed it must as well thus preserved, for otherwise it could be activated even without the lid having been screwed up, because the battery could be in contact with the walls of the tube. In placing the two batteries within the insulating pipe, care must be taken to prevent any possible electrical crossing between them.
- The placement of the batteries in the transmitter is the same for all makes (except in some rare cases) - the negative pole of the first battery must be placed in contact with the centre of the battery-holder, and its positive one, that of the body, must be in contact with the negative pole of the second battery. This is called configuration in series, so that the voltages are summed up.
- The battery checkers for conventional batteries don't help much as regards our confidence after having checked the batteries of a transmitter. The reason is that the conventional checkers don't show the percentage of the battery power. When a battery that is due to be used in a watch is checked the checking is valid, because the consumption is so low that the watch can still work when the battery is at 10% of its capacity. Unfortunately, transmitters (excepting some used in wildlife) consume much current, because the question is to get the maximum range for few days of lifetime. This leads us to the conclusion that we may be using batteries that have satisfactorily passed the checking and within just a few hours stop working. As a rule, the batteries should be replaced at half the lifetime indicated by the maker. Even if there are much more sophisticated checking systems, more often than not they are not available because they are either very expensive or very hard to manage. If in spite of everything a conventional checking system have to be used, the battery must be connected as little time as possible, because there is a partial discharge while connected. On the other hand, if a set of batteries is used, each of them must be checked individually.
Mainly four different kinds of batteries for the transmitters are used:
1°) Silver oxide batteries (button-type, 1.5 V)
They are the most commonly used on account of the large range of models available, which means a great flexibility when deciding which one is most suitable for each transmitter. The batteries must always be those recommended by the maker, because there are basically two types, low-drain batteries (which are used in alarm- and light-less watches, but never in transmitters), and high-drain ones, the kind we must use. Since the dimensions of both types are identical, there can be some confusion. Let us take Maxell 357 battery as a reference, with a capacity of 165 mA/H, and then compare the four categories.
They can be kept for up to three years with a minimal lifetime loss.
2°) Litium batteries (button-type, 3 V)
They are not as extensively used in falconry as silver-oxidum ones, because there is a shorter range of small diametres and they are more expensive than the latter. Their instant energy, especially as regards the button-type ones, is limited, so they are not suitable for high-power transmitters. Special, larger models exist, with a higher instant current, which are widely used in wildlife transmitters.
One instance of a litium batery for falconry is the 2L76 by UCAR, 165 mA/h, with quite the same performance as two 357 joined together - 3V 165 mA. A litium battery can be kept for as long as 10 years with a minimal lifetime loss
3°) Mercury batteries (button-type, 1.4 V)
Even if they have a higher capacity than the former, they are falling into desuse out of their pollutant efects to the environment, so the makers are relinquishing their production.
The capacity for the mercury battery 675 is 270 mA. They produce higher instant currents.
4°) Air-zinc batteries (button-type 1.4 V)
They have the highest capacity. They are widely used in deaf aids. There is an abundant range of sizes, similar to that of silver-oxide batteries. Taking as a reference the size 357 (silver-oxide) we have the ZA675, with 520 mA., which means two times the life-time of the mercury battery and three times that of the silver-oxide ones. Unfortunately, these batteries usually have an adhesive label stopping one or two holes of the flat face of the battery, which prevents the air from passing through it. If the holes are stopped by attaching two batteries, they will not yield the maximum current capacity. Eventhough the maker advises to remove the label just a few minutes before using the battery, we have verified it is better to do so at least one day before. If we wonder why the label is placed, we can say that it is in order to preserve it, because in a way it is as though removing the label would be the last phase of the making of the battery. If we want to get the maximum performance of the battery, we should always have a set of batteries in reserve ready at hand, without fastening them together, their labels removed.
When they are due to be used, it would be highly recommendable, in order for the batteries to have air, to have thin metallic washers of a good conductive material, 0.1 mm thick, the diameter slightly smaller than that of the battery, with a cutting so as to better let the air pass through. One washer should be placed for each battery, and the plastic pipe designed to fasten two batteries together and insulate them from the aluminum tube must be cut in such a way so as to let the air in both of the batteries independently. It seems very complicated, but if done with precision, a lifetime of up to 24 days can be achieved for our 50-km-range transmitters, instead of the 8 days with two batteries 357.
216 MHz or 432 MHz (VHF or UHF) ?.
216 MHz Advantages.
- The receiver is cheaper than the 432 MHz one.
- Proportionally the transmitters work with higher lifetime and power.
- The penetration in vegetation is higher than with the 432 MHz reveiver.
- The range is theoretically higher than that of the 430 MHz receiver (but it is usually lower because of the electrical noise, much higher than that of the 430 MHz receiver).
- The difraction is higher.
216 MHz disadvantages.
- In order to get the maximum range, the transmitter antenna must be 35 centimetres long, which corresponds to 1/4th of the wavelength, even though 23-cm-long antennae (compensated) are made, but with a loss of 50% of the range if compared with the 35-cm-long one. With the 430 MHz band the transmitter antenna is 17 cm long, without loss of range because that is the suitable size for the frequency.
This is very important, in order to prevent the bird from getting electrocuted.
- Interference from industrial machinery, high-tension cables, etc. may prevent the reception of weak signals. This can be to a certain extent avoided by using a 432 MHz receiver instead.
- The receiver antenna is somewhat cumbersome for the 216 MHz model. Instead, our 432 MHz model has a compact two-element folding antenna, as well as a comfortable handle, which is extraordinarily easy to use, proving very agile in the tracking, since it is as well possible to use it from inside the car.
- Lower reflection than the 432 MHz model. Higher difraction with trees, whick provokes errors in the tracking, especially in vertical polarization.
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