The feedhorn is a device that collects the signals at the focus of the satellite dish and channels them to the LNB (Low Noise Block Down Converter). The LNB amplifies the received signals (3.6 - 4.2 GHz for C-band or 12.25 - 12.75 GHz for Ku-band) and converts them to lower frequency in the range between 950 and 2150 MHz, and are then sent down a cable to the satellite receiver.
To receive both C-band and Ku-band signals, you need a dual band feedhorn with both C-band and Ku-band LNBs. If you want to receive programmes from both vertical and horizontal polarisations, you will need a feedhorn providing outputs for both polarisations. Furthermore, by installing a dual-band and dual-pol feedhorn, you can receive signals from both C and Ku bands and each band having signals from both vertical and horizontal polarisations simultaneously
A satellite receiver is a unit which takes signals from the LNB(s) and decodes the TV video and audio so they can appear on TV. Because both C-band and Ku-band LNBs normally have the same output frequency, which is from 950 - 2150 MHz, a receiver shall be capable of receiving either C-band or Ku-band programmes.
An analogue receiver is needed for the reception of analogue channels whereas a digital receiver to receive digital channels. To watch television channels that are encrypted or conditional access, you need a special Integrated Receiver Decoder (IRD) which is normally supplied by the broadcasters or cable operators.
Since a domestic satellite receiver is designed for 1:1 reception, i.e. one input and one output, you need more receivers and use a n:1 AV selector to collect all signal inputs if your system has more than one incoming signal e.g. dual polarisation or dual band
How to Retrofit Existing Single Feed TVRO?
Set Up Configuration
Retrofit the existing C-band TVRO dish that has a single feed and LNBs pointing to either AsiaSat 3S or AsiaSat 5
Install a secondary feed assembly and LNBs to the existing TVRO dish
Connect the IF cable to the additional LNBs
Align the secondary feed horn and optimise the additional feed position for best quality signal
Rotate the secondary feed to get the right polarisation angle
Once obtain the best C/N ratio, fix the LNBs at the selected position
Installation of the secondary feed is complete when achieve the maximum signal levels of both satellites
Details of Aligning the Additional Feedhorn
To receive more than one satellite simultaneously using one dish antenna, you need to find out two additional angles to fix the supplementary feedhorn besides the Azimuth and Elevation angles of the primary satellite. They are the "Relative Separation Angle" and "Feed Offset Angle".
The relative separation angle is used to align the supplementary feedhorn on the transversely displaced feed point of the secondary satellite. Feed offset angle is used to find out the position of the supplementary feedhorn.
Imagine that there are two planes, Plane 'A' and Plane 'B', along the antenna axis. Plane 'A' is at the back of the antenna and Plane 'B' is in front of the feedhorn. If AsiaSat 5 is the primary satellite, align the dish antenna with AsiaSat 5 first. Then find out the position of the secondary satellite (i.e. AsiaSat 3S) on plane 'A' and the position of the secondary feedhorn on plane 'B'. Align the secondary feedhorn with the secondary axis by connecting these two points.
To receive both AsiaSat 3S and AsiaSat 5 using a 2.4m dish antenna in Hong Kong, and assuming AsiaSat 5 is the primary satellite and AsiaSat 3S the secondary satellite, the
relative separation angle will be5.24° H2.43° Vfeed offset angle will be-0.102m H-0.047m Vwhere H is horizontal direction and V is vertical direction
In the case of receiving two satellites with a single dish, the receiving gain for the secondary satellite will be lower than that of the primary satellite. In order to compensate this loss, a large antenna or signal booster may be needed.