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what is Receiver?

what is Receiver?

The electromagnetic signal received by the antenna is sent to the receiver.The ideal receiver inhibits all unwanted noise, including other signals, and does not add any noise or interference to the required signal.Regardless of the form and format of the signal, it can be transformed to fit the desired characteristics of the signal processor detection circuit and then to the intelligent user interface.

structure

The receiver has two basic structures, one is superhetrodyne structure and the other is the direct transformation structure.

A superheterodyne receiver, is the received radio frequency signal with a frequency of the vibration signal mixing or next after frequency conversion output frequency of a low intermediate frequency modulation signal . The frequency of the intermediate frequency signal is the fixed frequency difference between the oscillator signal and the frequency of the received signal. The demodulation of the final signal is that the medium frequency signal is filtered and enlarged and finished by the demodulator in the middle frequency.

These receivers of direct conversion , its basic principle is same as heterodyne receiver, the difference is that the vibration frequency of the mixing  is not any given, but is equal to the carrier frequency, this  intermediate frequency is going to be zero, so there is no mirroring frequency and the mirror frequency interference, this plan is often referred to as the zero intermediate frequency.The rf part of the scheme eliminates the mirror frequency filter, while the intermediate frequency filter becomes the low-pass filter, simplifies the composition of the system, reduces the difficulty of design and implementation, and saves the cost. .However, there are obvious shortcomings in the direct conversion of the receiver, such as the frequency and carrier frequency of the vibration, it is easy to cause the leakage of the vibration.There is a direct current deviation, which has serious impact on the subsequent circuit; It can only be used for the demodulation of the amplitude modulated signal, and cannot demodulate the modulation and phase-modulation signal.The stability requirement of this vibration is high, so most are only used in low frequency band.

Function

So many main functions of the receiver from the air waves, is to find the frequency components you need, inhibit or filter out unwanted signals or noise and jamming signal, and then amplify, get useful information on the original by demodulation .

characteristic test

The IEEE 802.16 d.2004 and IEEE 802.16 e.The test requirements for the receiver were defined in 2005

(1) receiver sensitivity;

(2) suppression of adjacent and alternate channels of receivers;

(3) the receiver's maximum input signal;

(4) maximum permissible signal of the receiver;

(5) suppression of receiver image.

Test items of there five receivers can be used to measure the deviation of receiver sensitivity.The receiver adjacent and alternate channel suppression test calls for an additional rf source to interfere with the signal source.This interference source must be the standard signal of OFDM modulation.

classification

Use classification

1. Navigation receiver:This type receiver is mainly used for the navigation of sports vehicles, which can give the position and speed of the carrier in real time.This kind of receiver generally adopts C/A code pseudo distance measurement, with low accuracy of single point real-time positioning, generally being plus or minus 25mm, and the influence of SA is plus or minus 100mm.Such receivers are cheap and widely used.Depending on the application field, the receivers can be further divided into: vehicle-mounted type for vehicle navigation and positioning;Nautical type -- for navigation and positioning of ships;Aviation - for aircraft navigation and positioning.Because of the speed of the aircraft, the receiver used in aviation is required to adapt to the high-speed movement.Star carrier - navigation positioning for satellites.Because the speed of the satellite is as high as 7km/s, the requirement for the receiver is higher.

2. Geodetic receiver: Geodesic receiver is used for precision geodetic measurement and precision engineering measurement with high positioning accuracy.Instruments are complex and expensive.The timing receiver of the receiver is often used in the time synchronization of the observatory and radio communications using the high accuracy time standard provided by GPS satellite.

Carrier frequency classification

1. Single frequency receiver: The single-frequency receiver can only receive the L1 carrier signal, and measure the carrier phase then determine the position ..The single-frequency receiver is only applicable to the precise positioning of short baseline (< 15km) because of the failure to eliminate the delay effect of the ionosphere.

2. Dual-frequency receiver.The dual-frequency receiver can receive L1 and L2 carrier signals simultaneously.The delay of the ionosphere can be used to eliminate the effect of the ionosphere on the delay of the electromagnetic signal, so the dual-frequency receiver can be used for the precise positioning of thousands of kilometers.

Channel classification

1. Multi-channel receiver

2. Sequential through channel receiver

3. Multi-channel multi-channel receiver

Classification of work principles

1. Code-related receiver: Code -related receiver is the pseudo - distance observation value using code-related technology.

2. Square receiver.Square type is to use the square of the carrier signal receiver technology to get rid of modulation signal, to restore the complete carrier signal, through the determination of phase meter carrier signal and the status of the receiver to receive the carrier signal, the phase difference between the determination of pseudorange observation.

3. hybrid receiver.This kind of instrument is the advantage of the above two kinds of receivers, which can obtain the code phase pseudo distance and also obtain the carrier phase observation value.

4. Interference type receiver.The receiver is to use the GPS satellite as the radio source, and to measure the distance between the two stations.