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Integrated Receiver Decoder (IRD)

IRD: IRD stand for Integrated Receiver Decoder. This is ultimately a signal receiver. The operational  sequence of IRD is reverse than that of the earth station. The received RF signal by LNB (low noise  blocker) is converted to low band frequency that is operational for IRD.The IRD process this low  band frequency then demodulate it and then decode it according to the encoding system (while  transmitted). And thus the desired base-band signal is recovered.


Figure: Down link System of a TV Channel


A professional IRD commonly used in satellite TV channel is Proview 7000 of Harmonic brand.


 Figure: Harmonic IRD Proview 7000

Azimuth and Elevation Angle (Antenna Look Angle) for Satellite tracking

Azimuth (Az)

The earth station needs to know where the satellite is in the orbit. Then the earth station engineer needs to calculate some angles to track the satellite correctly. These angles are called antenna look angle. The look angles for the ground station antenna are the azimuth and elevation angles required at the antenna so that it points directly at the satellite. With the geostationary orbit the situation is much simpler than any other orbit. As the antenna beam width is very narrow and tracking mechanism is required to compensate for the movement of the satellite about the nominal geostationary position. Three pieces of information that are needed to determine the look angles for the geostationary orbit are

a. Earth station latitude
b. Earth station longitude
c. Satellite orbital position

Using these information antenna look angle can be calculated using Napier’s rule (solving spherical triangle). Azimuth angle denotes the horizontal angle measured at the earth station antenna to north pole. Elevation is such angle denotes the vertical angle measured at the earth station antenna end from ground to satellite position.


Figure : Antenna azimuth angle


Equation for Azimuth (Az) determination

Here G = Difference between satellite orbital position and earth station antenna.
          L = Latitude of your earth station antenna. 



Elevation (El)

In the above picture Az means azimuth angle required to track the satellite horizontally. In the figure below the elevation angle has been shown.
 
Figure : Antenna elevation angle



Equation for Elevation (El) determination









Here 0.1512 is constant


Note
1) If the satellite orbital location is in east (E), then G = Antenna longitude  - Satellite orbital position.
2) If the satellite orbital location is in West (W), then G = Satellite orbital position - Antenna longitude


Online azimuth and elevation calculator

Sun Outage Problem in Satellite TV Channel


Sun Outage or Sun Transit or Sun Fade
Geostationary satellites are fantastic means of communication except for one little problem called sun outage or sun transit or sun fade. It is an interruption in or distortion of geostationary satellite signals caused by interference from solar radiation.  Because the sun is a powerful broadband microwave source and has a noise temperature. The elevated temperature of the sun causes it to transmit a high-level electrical noise signal to the receiving systems. For that reason when the sun passes directly behind the satellite (when viewed from earth) that means the sun is in direct line with a communication satellite,  reception of the relatively weak satellite signals is affected. Due to the many differences in ground station equipment, some stations may experience a complete loss of signal while others may only experience a tolerable degradation of signal.


Figure: Graphical representation of sun outage problem.

A most common video on sun outage problem


When it Occur
A sun outage typically occurs around the time of the equinoxes. This natural  illusion happens twice a year when a satellite and a receiving earth station come directly in line with the sun. In the northern hemisphere, sun outages occur before the March equinox (February, March) and after the September equinox (September and October), and in the southern hemisphere the outages occur after the March equinox and before the September equinox. The sun radiates strongly across the entire spectrum, including the microwave frequencies used to communicate with satellites (C-band, Ku band, and Ka band). So the sun swamps the signal from the satellite.

How long do they last?
For geostationary satellites, the solar outage can typically cause disruption to the received signal for a few minutes each day for a few days. It will last longer the smaller the antenna involved. A 40cm dish will have a longer period of interference than a 120cm dish. This is because a small dish has a greater signal acceptance angle than a big dish.

How do they affect watching TV?
The effects of a sun outage range from partial degradation (increase in the error rate) to total destruction of the signal. During this time interference may occur with picture quality and sound when watching television. Sun outages do not affect internet or phone service. 

Sun Outage Prediction Parameter
Time, date and duration of sun outage problem depends on some parameters.
  • Latitude of the receiving antenna
  • Latitude of the satellite
  • The diameter of the receiving antenna
  • The beam width of the receiving antenna
  • The apparent radius of the sun as seen from the Earth (about 0.25°)
  • The RF energy given off by the sun
  • The transmitter power of the satellite
  • The gain and S/N performance of the ground station receive equipment and other factors
Outage Angle
Those parameter can be used to determine the outage angle of the receive antenna. Outage angle is defined as the separation angle (measured from the ground station antenna) between the satellite and sun at the time when sun outage or signal degradation begins or ends.



Figure: sun outage angle.







Frequency = Down link Frequency in GHz.
Diameter = Dish diameter of ground station receive antenna in meters.



Connector used in TV Channel Part-1

In broadcast engineering industry, there have to use various connector and cable for different purpose. Here I will describe some connector with image and usage.

Connector # 1
Connector Name: XLR Connector
Usage: It is mainly used for audio signal connectivityBeside this it is used for stage lighting equipment,  low-voltage power supplies and other applications. It has 3 to 7 pins.
Image:
 Figure: XLR Connector

 Figure: Cable connection of 3 pin XLR Connector.



Connector # 2
Connector Name: BNC (Bayonet Neill–Concelman or British Naval Connector or Bayonet Nut Connector) Connector
Usage: BNC connector is attached to the ends of coaxial cables. It can be used for connecting RF signals, aerospace electronics and video (analog and digital) signals. It is the alternative to RCA for professional video. Home usage electronics appliance such as televisions and DVD players etc. have BNC connectors as long as RCA connector to deliver composite video.
Most commonly used BNC connector are two types depending on their impedence, 50 ohms and 75 ohms. These connector are matched with the cable of same characteristic impedance. Video (particularly HD video signals) use 75 ohm BNC connectors, whereas 50 ohm connectors are used for data and RF.


Figure:  75 ohms and 50 ohms BNC connector.

Difference between 50 and 75 Ohm BNC connectors: Dieletric material at the interface of the 75 Ohm version is absence. Another difference is 50 ohm impedance for applications up to 4 GHz and 75 ohm impedance up to 2 GHz.

 Figure: Difference betwen 75 ohms and 50 ohms BNC connector.

Image: 
 

 Figure:  BNC connector


 
  
Figure:  Various parts of BNC connector.


Connector # 3
Connector Name: BNC inline coupler video connector or BNC I connector.
Usage: To connect two BNC male connector.
Image:
  Figure: BNC I connector.




Connector # 4
Connector Name: BNC T Connector (BNC Male to BNC Double Female Splitter) 
Usage: To take video signal from one BNC male connector and transmit this same signal through two female BNC connector.
Image:

Figure: BNC T connector.