Building a custom satellite system & choosing a non-proprietary satellite receiver

Choosing the dish and receiver

Unlike Sky Digital, there are several things to consider when choosing equipment for viewing encrypted European TV channels. With Sky Digital, they have a basic fixed dish set-up and the choice of either a standard digital receiver or a Sky+ receiver that incorporates a hard drive based digital video recorder.

The main thing to consider is what type of dish will be required. For a fixed dish set-up with up to four dishes, a DiSEqC 1.0 capable receiver would be sufficient. For a steerable dish set-up, at least DiSEqC version 1.2 is required. DiSEqC is a signalling system that the receiver sends out over the LNB cable to tell the DiSEqC switch or motor which satellite to choose. DiSEqC motors require additional power to be fed on the LNB cable to power them. For larger motorised dishes (over 1 Metre) it may be worth considering a 36 volt actuator and positioner.

The next choice is deciding whether to go for a PC based satellite receiver or a set-top box. A set-top box would be best suited for watching satellite TV on a standard television set similar to a Sky based system. A PC based system uses a DVB PCI card to receive the satellite transmissions and has several advantages such as easy and cheap to update, PVR as standard and easy to use. The main disadvantage with a PC solution is that the PC is always in use while watching TV and it is rather difficult to set-up a remote control for.


Components

Whether choosing a PC based or set-top box solution, there are several stages to converting the beamed down satellite signal to a viewable picture. The following sections explain each step on the path between the dish and receiver.


Satellite Dish Set-up

A satellite dish works similar to a TV antenna with the exception that it is intended to pick-up the weak ultra high frequency satellite transmissions, down-convert the frequency and place them on the coaxial cable. The Dish is made up of several components – The dish itself, an LNB and an actuator for motorised dishes.



Satellite Dish

The purpose of the satellite dish is to focus the signals down to a fine point on the LNB. The greater the surface area of the dish is, the greater the signal received gets. The size of the dish is important when it comes to receiving weak signals.

LNB - Low Noise Block

The LNB down-converts the high frequency satellite signals (10.7GHz to 12.75GHz) down to a lower frequency band (around 2GHz to 3Ghz) to carry on the coaxial cable. The LNB runs on two different voltage levels and uses a 22kHz tone to determine which band to select. Satellite signals are transmitted in either horizontal or vertical polarisation and the voltage sent down the coaxial from the receiver tells the LNB which polarisation to choose. A Universal LNB will either convert 10.7GHz to 11.7GHz or 11.7GHz to 12.75 GHz to the lower band, which can be transferred on the coaxial cable. If the LNB detects a 22kHz tone on the cable, it will choose the higher band; otherwise the lower band will be down-converted.

Due to the different bands and polarisation the receiver has to choose from, only one LNB output feed can be tuned per satellite receiver. If two or more receivers must be connected to the same dish, a LNB is required with at least enough outputs to connect to each receiver without splicing the cable.

LNB’s come in different noise levels. The lower the noise level, the better the signal to noise ratio gets. Lower noise levels help improve the reception of weak channels when the dish size cannot be easily increased. Note that it is important to go for the maximum dish size affordable or allowed before deciding on paying out for a lower noise LNB.

DiSEqC 1.2 Motor / Actuator

Satellite dishes can only pickup transmissions from a fixed point in the sky. For example a dish pointing to Astra 19.2E will not pickup transmission at 16E at the same time. To pick-up multiple satellite positions with a single dish, a mortised system is required to move the dish to the required position.

There are various DiSEqC 1.2 motors available to suit the majority of small and large dishes on the market. They are all require at least DiSEqC 1.2 support on the satellite receiver and enough power output to drive the motor. DiSEqC 1.2 provides the power on the same cable that picks up the signal, however larger 36 volt actuators use a separate power cable and dish positioner to move the dish.

Due to the length of time it takes for a DiSEqC switch to move the dish from one satellite point to the next, it may be worth considering a multiple LNB / dish set-up if 4 or less satellite positions will be required. For example, moving a dish from BBC Digital at 28.2E to Hispasat at 30W can take several up to several minutes for a basic DiSEqC 1.2 motor.

DiSEqC 1.0 / 2.0 n-way Switch

The purpose of a DiSEqC switch is to allow multiple satellite dishes (or multi-LNB dishes) to be connected to a single satellite receiver. The advantage with a multi LNB / dish set-up over a mortised solution is fast switching between channels across multiple satellite positions.

A-B n-way switch

Like a DiSEqC switch, an A-B switch allows multiple dishes to be hooked up to a single satellite receiver, however the user must manually select the satellite to use by the switch. Some switches can also work in reverse to allow multiple receivers to operate from the same dish or set of dishes, however only one receiver may operate at a given time. This is useful when connecting a PC DVB card and set-top box to the same dish when only one is in use at a given time.

Signal Meter

The main purpose of a signal meter is to indicate if a signal is being received on a cable from a dish. Signal meters range from vary basic models which just beep when a signal is detected all the way up to high end models which show the satellite position, signal strength, diseqc signals, polarity and signal to noise ratio.

It is generally worth considering a meter with some sort of signal strength indication such as a needle or 7 or more LEDs. These usually have a sensitivity knob for fine-tuning on both weak and strong satellites.

To use a basic signal meter, connect it inline with the LNB cable and tune the satellite receiver on to a known channel from this dish. Adjust the sensititivity until the needle or LED position is about a quarter. Then slowly move the dish left/right or up/down until the signal indicator increases. If the needle or LED position goes beyond 3/4 of the graph, lower the sensitivity knob until the indication moves to the middle and continue adjusting. Once the optimal position is achieved, tighten any nuts and finally adjust the LNB skew to give the best reading.

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Last edited by seanbyrne; 05-08-2004 at 11:08.

Note: The channel selections mentioned below are based on choosing a satellite receiver in Europe since this is what I am familiar with. Similar rules will apply to choosing receivers in other continents also


Satellite Receiver

As with Sky digital, a digital satellite receiver is required to decode the satellite transmissions into a format that can be displayed on screen. The receiver works by sending out power on the coaxial cable to power the LNB and the Diseq switch if present. It also sends out different voltage levels, tones and Diseq commands to tell the LNB which band to pick-up as well as what satellite to choose on a motorised or multi-dish set-up.

There are several types of digital receivers to choose from. Analogue satellite receivers are gradually becoming obsolete. An analogue receiver can only pick up analogue transmissions where as a digital receiver can only pick up digital transmissions.

FTA Receivers

The most basic digital receiver is known as a FTA system which means that it can only pick up free-to-air transmissions. FTA systems are relatively cheap and are mainly intended for those who just want to improve their channel selection or pick up the BBC digital channels selection where terrestrial BBC reception whether analogue or digital is weak or not available. These are also known as BBC systems or God channels receivers since both sets of channels are not encrypted.


Receivers capable of decoding encrypted transmissions

For the reception of encrypted channels, a digital receiver with either a built-in CAM or removable CI slots is required along with a suitable viewing card. For the best customisability, it is best to choose a receiver with at least one or more CI slots to allow for future expansion.


The CAM – Conditional Access Module

A CAM is a module that decrypts one or more encryption systems. In the early days of analogue transmission, a decoder (descrabler) use to be a physical set-top box which connected to the receiver. Now the decoders are in the form and size of PC Cards known as CAMs which plug directly into a receiver with CI slots. Like with a physical set-top decoder, most CAMs require a suitable viewing card in order for the CAM to derypt channel the user is entitled to watch.

The most popular encryption systems in use are Viacess, Irdeto, Nagravision, Betacrypt, Seca, Videoguard and Conax. Seca is also known as Mediaguard and Videoguard is also known as NDS. Many receivers come with a built-in cam, which can either receive one of these or all of these. For receivers with one or more CI slots, a PC-Card type CAM (PCMCIA) can be installed for decoding additional encryption systems.

The most popular multi-encryption support CAM’s at present are the Magic Module and the Matrix Reloaded CAM. Both of these are capable of decrypting most of the above encryption systems with an appropriate viewing card (and subscription). Note that these programmable CAM’s are often supplied blank for legal reasons and must be programmed with the appropriate downloadable firmware prior to use. Dedicated encryption CAM’s such as a Viaccess CAM are supplied ready for use.

Note that while Sky uses the Videoguard (NDS) encryption system, there are no PC Card CAMS available which can handle Videoguard. Decryption support is only available as an intregated CAM with a proprietary Videoguard system such as the receivers offered by Sky Digital.


Other Features

Besides TV, radio and encryption support many receivers off various other features that the consumer may be interested in looking out for. These include digital audio out or pass-thru, Teletext decoding, EPG, Diseq, PVR and 36 volt output.

Teletext – Nearly all digital receivers on the market offer Teletext decoding support. Unlike terrestrial analogue TV, the satellite video, audio and Teletext streams are separate from each other. When a receiver with Teletext support detects the Teletext stream (PID), it will add it to the field lines of the picture to enable Teletext viewing from a Teletext compatible TV.

EPG – Electronic Programming Guide is a useful feature to determine what is on next or at a later stage. Most satellite channels provide what is currently on and the next programme. Some channels even provide the schedule up to a week or two ahead. Some satellite receivers allow the user to choose programmes to record. Once a chosen programme time has reached the receiver changes over to the appropriate channel for the duration of the programme.

Diseq – Diseq is a signalling system which the receiver sends out to control Diseq switches and Diseq based motorised dishes. Diseq v.1.0 can operate either a 2-way or 4-way Diseq switch. Diseq v.1.2 operates a low power Diseq 1.2 motor with dish sizes up to around 1 metre.

PVR – PVR support allows the satellite receiver to function in the same way as a TV based PVR. With PVR support, the user can pause live broadcasts as well as select EPG programmes or a scheduled times to watch later. Note that PVR systems usually have two cables from the dish. One is for live viewing and the other is for the PVR, which allows the user to watch one channel while recording another. PVR systems with only one input will not allow the user to change channel while it is recording a programme.

36 Volt Output – Receivers with a 36 volt out allow the motorised control of a large motorised dish setup with a separate power cable to the motor. The advantage of having the power supply built in is that the user does not need to operate a separate power supply to move the dish.