There
are three ways in which the bandwidth of the channel carrier may be
altered simply. It is worth emphasising that these methods are chosen
because they are practically simple, not because they are theoretically
desirable. These are the altering of the amplitude, frequency and phase
of the carrier sine wave. These techniques give rise to amplitude-shift-keying (ASK) , frequency-shift-keying (FSK) and phase-shift-keying (PSK) , respectively.
ASK describes the technique the carrier wave is multiplied by the digital signal
. Mathematically, the modulated carrier signal
is:

Figure: Amplitude shift keying

Figure: Amplitude shift keying -- frequency domain
It is a special case of amplitude modulation (AM) . Amplitude modulation has the property of translating the spectrum of the modulation
to the carrier frequency. The bandwidth of the signal remains unchanged.
The
fact that AM simply shifts the signal spectrum is often used to convert
the carrier frequency to a more suitable value without altering the
modulation. This process is known variously as mixing , up-conversion or down-conversion .
Some form of conversion will always be present when the channel carrier
occupies a frequency range outside the modulation frequency range.
FSK describes the modulation of a carrier (or two
carriers) by using a different frequency for a 1 or 0. The resultant
modulated signal may be regarded as the sum of two amplitude modulated
signals of different carrier frequency

Figure: Frequency shift keying

Figure: Frequency shift keying -- frequency domain
FSK
is classified as wide-band if the separation between the two carrier
frequencies is larger than the bandwidth of the spectrums In this case
the spectrum of the modulated signal appears as two separate ASK
signals. Narrow-band FSK is the term used to describe an FSK signal
whose carrier frequencies are separated by less than the width of the
spectrum than ASK for the same modulation.
PSK describes the modulation technique that alters the phase of the carrier. Mathematically:
Binary phase-shift-keying (BPSK) has only two phases, 0 and
. It is therefore a type of ASK with
taking the values -1 or 1 , and its bandwidth is the same as that of
ASK. Phase-shift-keying offers a simple way of increasing the number of
levels in the transmission without increasing the bandwidth by
introducing smaller phase shifts. Quadrature phase-shift-keying (QPSK) has four phases,
. M-ary PSK has M phases,
. For a given bit-rate, QPSK requires half the bandwidth of PSK and is widely used for this reason.

Figure: Binary phase shift keying
The number of times the signal parameter (amplitude, frequency, phase) is changed per second is called the signaling rate . It is measured in baud .
1 baud = 1 change per second. With binary modulations such as ASK, FSK
and BPSK, the signaling rate equals the bit-rate. With QPSK and M-ary
PSK, the bit-rate may exceed the baud rate.
Product ID: TM01
433.92MHz ASK TRANSMITTER MODULE
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Specifications:
- SPECIFICATIONS
- DC CHARACTER
- Supply Voltage +8V?5%
- Current Consumption 20mA , Max
- RF
- RF output power ?10 dBm
- transmit frequency 433.92 MHz?150kHz
- Modulation AM
- WORK ENVIRONMENT
- Operation temperature 0 to 60 degree C.
- Storage Temperature Range -10~+85 șC
- Humidity 85%RH
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Product ID: R4D
ASK RECEIVER MODULE
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Specifications:
- SPECIFICATION
- DC CHARACTER
- Supply Voltage 2~5V
- Current Consumption 2.5mA?0.5mA
- Transportation Speed 2.4K bps
- sensitively -112dBm
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