Unit of competence:-install and repair

antenna and satellite system

Information sheet of Satellite dish
A satellite dish is a dish-shaped type of parabolic antenna designed to receive microwaves from
communications satellites, which transmit data transmissions or broadcasts, such as satellite television.
The parabolic shape of a dish reflects the signal to the dish’s focal point. Mounted on brackets at the dish's
focal point is a device called a feedhorn. This feedhorn is essentially the front-end of a waveguide that
gathers the signals at or near the focal point and 'conducts' them to a low-noise block downconverter or
LNB. The LNB converts the signals from electromagnetic or radio waves to electrical signals and shifts
the signals from the downlinked C-band and K u-band to the range. Downlink means receive and uplink
means transmitting.

Coaxial Cable
Coaxial cable is manufactured with a single copper wire at the center. This copper wire is surrounded by a
plastic sleeve. The plastic sleeve provides insulation between the single copper wire and a braided metal
mesh wrapped around the outer portion of the sleeve. The layer of metal mesh acts as a shield to block
interference from sources outside the cable, and prevents the center wire from radiating needless electrical
frequencies, thus maintaining steady power within the communication line. Some types of coaxial cable
contain an additional plastic layer, which provides protection against moisture reaching the center copper
wire.

Coaxial cabling has a single copper conductor at its

center. A plastic layer provides insulation between the
center conductor and a braided metal shield (See fig. 3).
The metal shield helps to block any outside interference
from

Fig. 3. Coaxial cable

 Coaxial Cable Connectors
The most common type of connector used with coaxial cables is the Bayone-Neill-Councilman (BNC)
connector. Different types of adapters are available for BNC connectors, including a T-connector, barrel
connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid
problems with your network, always use the BNC connectors that crimp.

Low noise block ( LNB )

The abbreviation LNB stands for Low Noise Block. It is the device on the front of a satellite dish that
receives the very low level microwave signal from the satellite, amplifies it, changes the signals to a lower
frequency band and sends them down the cable to the indoor receiver.

The expression Block refers to the conversion of a block of microwave frequencies as received from the
satellite being down-converted to a lower (block) range of frequencies in the cable to the receiver.
Satellites broadcast mainly in the range 4 to 12 to 21 GHz.

Low noise block down converter (LNB) diagram

The diagram shows the input waveguide on the left which is connected to the collecting feed or horn. As
shown there is a vertical pin through the broad side of the waveguide that extracts the vertical polarisation
signals as an electrical current. The satellite signals first go through a band pass filter which only allows
the intended band of microwave frequencies to pass through. The signals are then amplified by a Low
Noise Amplifier and thence to the Mixer. At the Mixer all that has come through the band pass filter and
amplifier stage is severely scrambled up by a powerful local oscillator signal to generate a wide range of
distorted output signals. These include additions, subtractions and multiples of the wanted input signals
and the local oscillator frequency. Amongst the mixer output products are the difference frequencies
between the wanted input signal and the local oscillator frequencies. These are the ones of interest. The
second band pass filter selects these and feeds them to the output L band amplifier and into the cable.
Typically the output frequency = input frequency - local oscillator frequency. In some cases it is the other
way round so that the output frequency = local oscillator frequency - input frequency. In this case the
output spectrum is inverted.

Examples of input frequency band, LNB local oscillator frequency and output frequency band are shown
below.

Input frequency
Local Oscillator Output L band into
band from satellite Input band GHz Comments
(LO) frequency cable.
waveguide
inverted output
C band 3.4-4.2 5.15 950-1750
spectrum
3.625-4.2 5.15 950-1525 "
4.5-4.8 5.75 950-1250 "
4.5-4.8 5.95 1150-1450 "

Ku band 10.7-11.7 9.75 950-1950

10.95-11.7 10 950-1700
Invacom SPV-
10.95 - 12.15 10 950-2150
50SM
11.45-11.95 10.5 950-1450
11.2-11.7 10.25 950-1450
Invacom SPV-
11.7-12.75 10.75 950-2000
60SM
Invacom SPV-
12.25-12.75 11.3 950-1450
70SM
11.7-12.75 10.6 1100-2150

More complex LNBs exist, particularly for satellite TV reception where people wish to receive signals
from multiple bands, alternative polarizations, and possibly simultaneously.

Dual-band LNBs
These will typically have two alternative local oscillator frequencies, for example 9.75 GHz and 10.6 GHz
with the higher frequency option selected using a 22 kHz tone injected into the cable. Such an LNB may
be used to receive 10.7 - 11.7 GHz using the lower 9.75 GHz LO frequency or the higher band 11.7 -
12.75 GHz using the higher 10.6 GHz LO frequency.

Dual polarization LNBs

The LNB shown above has one wire going into the waveguide to pick up vertical polarization. If the input
waveguide is circular is can support two polarizations and it can be arranged for there to be two input
probes at right angles, thus allowing two alternative polarizations to be selected (vertical or horizontal, or
left hand or right hand circular polarization, LHCP or RHCP), either one or the other. Dual polarization
LNBs may commonly be switched remotely using two alternative DC supply voltages. e.g. 13 volts
makes it receive vertical polarization and 19 volts make it receive horizontal polarization.
Multi-LNBs
If both input probes have their own LNB amplifiers etc you have effectively two LNBs in the same
module, which will have two output cables, one for each polarization. Many variants on this theme exist,
with options also for multiple bands. Such a "Quad LNB" might thus have 4 outputs, for each polarization
and each of two bands. Such an arrangement is attractive for a block of flats, head end antenna, which
need to feed multiple indoor satellite TV receivers with the viewers all wanting all permutations of the two
polarizations and two frequency bands.

LNB supply voltages

The DC voltage power supply is fed up the cable to the LNB. Often by altering this voltage it is possible
to change the polarization or, less commonly, the frequency band. Voltages are normally 13 volts or 19
volts.
Perfect weatherproofing of the outdoor connector is essential, otherwise corrosion is rapid. Note that both
the inner and outer conductors must make really good electrical contact. High resistance can cause the
LNB to switch permanently into the low voltage state. Very particular effects can occur if there poor
connections amongst multiple cables to say an LNB and to a transmit BUC module as the go and return
DC supplies may become mixed up and the wrong voltage applied across the various items. The electrical
connections at the antennas between the LNB and the BUC chassis are often indeterminate and depend of
screws in waveguide flanges etc. Earth loop currents may also be a problem - it is possible to find 50 Hz
or 60 Hz mains currents on the outer conductors - so be careful. Such stray currents and induced RF fields
from nearby transmitters and cell phones may interfere with the wanted signals inside the cables. The
quality and smoothing of the DC supplies used for the LNBs is important.

How to test an LNB:

Check with a current meter that it is drawing DC current from the power supply. The approx number of
milliamps will be given by the manufacturer. Badly made or corroded F type connections are the most
probable cause of faults. Remember that the centre pin of the F connector plug should stick out about
2mm, proud of the surrounding threaded ring.

Use a satellite finder power meter. If you point the LNB up at clear sky (outer space) then the noise
temperature contribution from the surroundings will be negligible, so the meter reading will correspond to
the noise temperature of the LNB, say 100K (K means degrees Kelvin, above the 0 K absolute zero
temperature). If you then point the LNB at your hand or towards the ground, which is at a temperature of
approx 300K then the noise power reading on the meter should go up, corresponding to approx 400K
(100K +300K).

Note that LNBs may fail on one polarization or on one frequency band and that the failure mode may only
occur at certain temperatures.

Low-noise block down converter

A low-noise block downconverter (or LNB) is the receiving device mounted on satellite dishes used for
satellite TV reception, which collects the radio waves from the dish. Also called a low-noise block, LNC
(for low-noise converter), or even LND (for low-noise down converter),the device is sometimes
wrongly called an LNA (low-noise amplifier).

The LNB is a combination of low-noise amplifier, frequency mixer, local oscillator and IF amplifier. It
receives the microwave signal from the satellite collected by the dish, amplifies it, and downconverts the
block of frequencies to a lower block of intermediate frequencies (IF). This down conversion allows the
signal to be carried to the indoor satellite TV receiver using relatively cheap coaxial cable; if the signal
remained at its original microwave frequency it would require an expensive and impractical waveguide
line.

The LNB is usually a small box suspended on one or more short booms, or feed arms, in front of the dish
reflector, at its focus (although some dish designs have the LNB on or behind the reflector). The
microwave signal from the dish is picked up by a feedhorn on the LNB and is fed to a section of
waveguide. One or more metal pins, or probes, protrude into the waveguide at right angles to the axis and
act as antennas, feeding the signal to a PCB inside the LNB's shielded box for processing. The lower
frequency IF output signal emerges from a socket on the box to which the coaxial cable connects.

LNBF disassembled (All Parts). The waveguide carrying the

microwave radio signal collected by the dish passes through
the hole in the center. The pins visible at the top and left
side of the hole project into the waveguide and receive the
signal, converting it to radio frequency alternating currents
which are processed by the circuit board.

The LNB gets its power from the receiver or set-top box
inside the house. This phantom power is sent "up" the same
coaxial cable that carries the received signals "down" to the
receiver, eliminating the need for a separate power cable.

A corresponding component, called a block upconverter

(BUC), is used at the satellite earth station (uplink) dish to
convert the band of television channels to the microwave uplink frequency.

Amplification and noise

The signal received by the LNB is extremely weak and it has to be amplified before downconversion. The
low noise amplifier section of the LNB amplifies this weak signal while adding the minimum possible
amount of noise to the signal.

The low-noise quality of an LNB is expressed as the noise figure (or sometimes noise temperature). This
is the ratio of the amount of noise in the output to the amount in the input, in decibels (dB). The ideal LNB
would have a noise figure of 0dB. Every LNB introduces some noise, although clever design, expensive
components and even individual tweaking of the LNB after manufacture, can reduce noise levels to very
low levels.

Block down conversion

Satellites use comparatively high radio frequencies (microwaves) to transmit their TV signals. The
purpose of the LNB is to use the superheterodyne principle to take a block (or band) of relatively high
frequencies and convert them to similar signals carried at a much lower frequency (called the intermediate
frequency or IF). These lower frequencies travel through cables with much less attenuation, so there is
much more signal left at the satellite receiver end of the cable. It is also much easier and cheaper to design
electronic circuits to operate at these lower frequencies, rather than very high frequencies of satellite
transmission.
The frequency conversion is performed by mixing a fixed frequency produced by a local oscillator inside
the LNB with the incoming signal, to generate two signals equal to the sum of their frequencies and the
difference. The frequency sum signal is filtered out and the frequency difference signal (the IF) is
amplified and sent down the cable to the receiver:

C-Band: IF frequency = local oscillator frequency - received frequency

Ku-Band: IF frequency = received frequency - local oscillator frequency

The local oscillator frequency determines what block of incoming frequencies is down converted to the
frequencies expected by the receiver. For example, to down convert the incoming signals from Astra 1KR,
which transmits in a frequency block of 10.70-11.70 GHz, to within a standard European receiver’s IF
tuning range of 950-2150 MHz, a 9.75 GHz local oscillator frequency is used, producing a block of
signals in the band 950-1950 MHz.

For the block of higher transmission frequencies used by Astra 2A and 2B (11.70-12.75 GHz), a different
local oscillator frequency converts the block of incoming frequencies. Typically, a local oscillator
frequency of 10.60 GHz is used to down convert the block to 1100-2150 MHz, which is still within the
receiver’s 950-2150 MHz IF tuning range.

In a C-Band antenna setup, the transmission frequencies are typically 3.7-4.2 GHz. By using a local
oscillator frequency of 5.150 GHz the IF will be 950-1450 MHz which is, again, in the receiver's IF tuning
range.

For the reception of wideband satellite television carriers, typically 27 MHz wide, the accuracy of the
frequency of the LNB local oscillator need only be in the order of ±500 kHz, so low cost dielectric
oscillators (DRO) may be used. For the reception of narrow bandwidth carriers or ones using advanced
modulation techniques, such as 16-QAM, highly stable and low phase noise LNB local oscillators are
required. These use an internal crystal oscillator or an external 10 MHz reference from the indoor unit and
a phase-locked loop (PLL) oscillator.

Polarization
It's common to polarize satellite TV signals because it provides a way of transmitting more TV channels
using a given block of frequencies. This approach requires the use of receiving equipment that can filter
incoming signals based on their polarization. Two satellite TV signals can then be transmitted on the same
frequency (or, more usually, closely adjacent frequencies) and provided that they are polarized differently,
the receiving equipment can still separate them and display whichever one is currently required.

Throughout the World, most satellite TV transmissions use vertical and horizontal linear polarization but
in North America, DBS transmissions use left and right hand circular polarization. Within the waveguide
of a North American DBS LNB a slab of dielectric material is used to convert left and right circular
polarized signals to vertical and horizontal linear polarized signals so the converted signals can be treated
the same.

The probe inside the LNB waveguide collects signals that are polarized in the same plane as the probe. To
maximise the strength of the wanted signals (and to minimise reception of unwanted signals of the
opposite polarization), the probe is aligned with the polarization of the incoming signals. This is most
simply achieved by adjusting the LNB's skew - its rotation about the waveguide axis. To remotely select
between the two polarizations, and to compensate for inaccuracies of the skew angle, it used to be
common to fit a polarizer in front of the LNB's waveguide mouth. This either rotated the incoming signal
with an electromagnet around the waveguide (a magnetic polarizer) or rotated an intermediate probe
within the waveguide using a servo motor (a mechanical polarizer) but such adjustable skew polarizers are
rarely used today.

The simplification of antenna design that accompanied the first Astra DTH broadcast satellites in Europe
to produce the LNBF extended to a simpler approach to the selection between vertical and horizontal
polarized signals too. Astra type LNBFs incorporate two probes in the waveguide, at right angles to one
another so that, once the LNB has been skewed in its mount to match the local polarization angle, one
probe collects horizontal signals and the other vertical, and an electronic switch (controlled by the voltage
of the LNB's power supply from the receiver: 13 V for vertical and 18 V for horizontal) determines which
polarization is passed on through the LNB for amplification and block-down conversion.

Such LNBs can receive all the transmissions from a satellite with no moving parts and with just one cable
connected to the receiver, and have since become the most common type of LNB produced.

Example LNBs
C-band LNB

Here is an example of a North American C-band LNB:

 Local oscillator: 5.15 GHz

 Frequency: 3.40-4.20 GHz
 Noise figure: ranges from 25 to 100 kelvins (uses kelvin ratings as opposed to dB rating).
 Polarization: Linear

Ku-band LNB

Standard North America Ku band LNB

Here is an example of a standard linear LNB:

 Local oscillator: 10.75 GHz

 Frequency: 11.70-12.20 GHz
 Noise figure: 1 dB typical
 Polarization: Linear

Universal LNB ("Astra" LNB)

Astra type LNBF

In Europe, as SES launched more Astra satellites to the 19.2°E orbital position in the 1990s, the range of
downlink frequencies used in the FSS band (10.70-11.70 GHz) grew beyond that catered for by the
standard LNBs and receivers of the time. Reception of signals from Astra 1D required an extension of
receivers' IF tuning range from 950-1950 MHz to 950-2150 MHz and a change of LNBs' local oscillator
frequency from the usual 10 GHz to 9.75 GHz (so-called "Enhanced" LNBs).

The launch of Astra 1E and subsequent satellites saw the first use by Astra of the BSS band of frequencies
(11.70-12.75 GHz) for new digital services and required the introduction of an LNB that would receive
the whole frequency range 10.70-12.75 GHz - the "Universal" LNB.

A Universal LNB has a switchable local oscillator frequency of 9.75/10.60 GHz to provide two modes of
operation – low band reception (10.70-11.70 GHz) and high band reception (11.70-12.75 GHz). The local
oscillator frequency is switched in response to a 22 kHz signal superimposed on the supply voltage from
the connected receiver. Along with the supply voltage level used to switch between polarizations, this
enables a Universal LNB to receive both polarizations (Vertical and Horizontal) and the full range of
frequencies in the satellite Ku band under the control of the receiver, in four sub-bands:[7]

Here is an example of a Universal LNB used in Europe:

 Noise figure: 0.2 dB typical

 Polarization: Linear

Supply Voltage Supply Tone LO Frequency Polarization Received Frequency Band Received IF Range Used

13 V 0 kHz 9.75 GHz Vertical Low (10.70-11.70 GHz) 950-1950 MHz

18 V 0 kHz 9.75 GHz Horizontal Low (10.70-11.70 GHz) 950-1950 MHz

13 V 22 kHz 10.60 GHz Vertical High (11.70-12.75 GHz) 1100-2150 MHz

18 V 22 kHz 10.60 GHz Horizontal High (11.70-12.75 GHz) 1100-2150 MHz

North America DBS LNB

Here is an example of an LNB used for DBS:

 Local oscillator: 11.25 GHz

 Frequency: 12.20-12.70 GHz
 Noise figure: 0.7 dB
 Polarization: Circular

Supply Voltage LO Frequency Polarization Received Frequency Band Received IF Range Used

13 V 11.25 GHz Right Hand Circular Polarization(RHCP) 12.20-12.70 GHz 950-1450 MHz

18 V 11.25 GHz Left Hand Circular Polarization(LHCP) 12.20-12.70 GHz 950-1450 MHz

Multi-output LNBs

An eight-output Octo LNBF

Dual/twin/quad/octo LNBs

An LNB with a single feedhorn but multiple outputs for connection to multiple tuners (in separate
receivers or within the same receiver in the case of a twin-tuner PVR receiver). Typically, two, four or
eight outputs are provided. Each output responds to the tuner’s band and polarization selection signals
independently of the other outputs and "appears" to the tuner to be a separate LNB. Such an LNB usually
may derive its power from a receiver connected to any of the outputs. Unused outputs may be left
unconnected (but waterproofed for the protection of the whole LNB).A special type of LNB intended for
use in a shared dish installation to deliver signals to any number of tuners. A quattro LNB has a single
feed horn and four outputs, which each supply just one of the K u sub-bands (low band/horizontal
polarization, high band/vertical polarization, low/vertical and high/horizontal) to a multiswitch or an array
of multiswitches, which then delivers to each connected tuner whichever sub-band is required by that
tuner.

Although a quattro LNB typically looks similar to a quad LNB, it cannot (sensibly) be connected to
receivers directly. Note again the difference between a quad and a quattro LNB: A quad LNB can drive
four tuners directly, with each output providing signals from the entire K u band. A quattro LNB is for
connection to a multiswitch in a shared dish distribution system and each output provides only a quarter of
the Ku band signals.

SCR LNB with three SCR taps for daisy-chaining multiple tuners