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What you must know before choosing a receiver
When choosing a receiver you must take into account the following
important aspects:
-Sensitivity
-dynamic range
-signal processing
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 this 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:
-130 dBm.
-140 dBm. Ten times as sensitive as -130 dBm (which is tantamount to
multiplying the transmitter power by ten)
-143 dBm. Twenty times as sensitive as -130 dBm (which is tantamount to
multiplying the transmitter power by twenty)
-146 dBm. Forty times as sensitive as -130 dBm (which is tantamount to
multiplying the transmitter power by forty)
-149 dBm. Eighty times as sensitive as -130 dBm (which is tantamount to
multiplying the transmitter power by eighty)
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 deffect 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.
Signal processing
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
distict, loud and long, even if the transmitter is many kilometres away. We can as well
greatly improve precision by
reducing the receiving angle which allows us a margin for error of very few centimetres.
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