Multifeed
Multifeed systems (or cross-eyed systems) are satellite reception systems that consist of a mirror, the multifeed bracket and at least two LNBs .
This makes it possible to receive two or more satellites (e.g. Astra 19.2 ° East and Hotbird 13 ° East). A separate LNB is required for each satellite. These are attached to a multifeed holder. This can be a simple mounting plate. Depending on the satellite, the distance between the LNBs must also be dimensioned accordingly. If only two satellites are to be received, a monoblock LNB can also be used. This has two horns which are exactly the distance (e.g. 6 ° or 3 °) to the satellites to be received, and often also an integrated multi-switch so that several receivers can be connected independently of each other. The disadvantage of monoblocks compared to real multifeed systems is that the exact angle between the satellites ( azimuth difference) depends on the location.
To switch between the satellites, a DiSEqC switch is required for simple LNBs . With Quattro LNBs, a so-called multi - switch with multiple LNB input is required. Monoblock LNBs have already integrated the multiswitch. In the past, 22 kHz switches were used instead of DiSEqC switches. However, this signal is used in digital systems for high-band / low-band switching, so DiSEqC is unavoidable in digital systems.
Compared to a motorized rotating system, a multifeed mirror has the advantage that when switching between the satellites there are neither noises nor noticeable delays and it can be used by several users independently of one another by means of a multi-switch. On the other hand, such an installation is always a compromise compared to LNBs installed in the center of individual mirrors or a rotating system. With a cross-eyed installation you have to decide on which of the satellites you want to focus the mirror and which satellite you want to receive cross-eyed (with a slight loss of reception power). Usually the mirror is focused on the less powerful satellite and the stronger satellite is received with a cross-eyed look. In Central Europe, multifeed installations with a focusing mirror at Hot Bird 13 ° East and squinting at Astra 19.2 ° East work very well for mirrors with a diameter of 60 cm or more. With cross-eyed systems, the price increases with the number of satellites to be received. DiSEqC switches for up to 10 positions, multifeed holders and LNBs are available cheaply for one-participant systems. With small mirrors, the minimum distance between two satellites is about 4.5 ° and decreases with increasing mirror size and lower latitude of the place of residence. The distance can also be reduced with LNBs that have a feed horn diameter of only 23 mm instead of the usual 40 mm (previously 60 mm was common).
Multifeed systems can easily be combined with multiswitches if a Quattro LNB is used per satellite, whereby multiswitches can sometimes be very expensive for many satellites and many participants. There are multiswitches with up to 32 IF levels and 12 participants. Since many satellites do not cover all four IF levels, multiswitches can then cover more satellites than would be expected (in this case more than 8).
In addition to the aforementioned combination of Hot Bird 13 ° East and Astra 19.2 ° East, the following combination of four satellites is common:
- Eutelsat Hot Bird , 13 ° East: free-to-air channels from almost every European and North African nation
- Astra 1, 19.2 ° East: many free-to-air channels from Germany and encrypted channels from Spain and France
- Astra 3, 23.5 ° East: channels from the Czech Republic and the Netherlands, both mostly encrypted
- Astra 2, 28.2 ° East: many free-to-air channels from Great Britain, although the major channels can only be received in western Germany without great effort
For this combination, TechniSat offers a fully assembled antenna with a diameter of 45 cm under the name Multytenne, but with such small mirror diameters there is no bad weather reserve. Since it is a monoblock of 4, the above restrictions apply. Any digital receiver with DiSEqC 1.0 support is suitable as a receiver for up to 4 positions.
The example opposite uses a parabolic mirror, which is relatively large for Central Europe with 125 cm. This became necessary because the desired satellite positions required a very close assembly of the LNBs and therefore required a relatively distant focus of the parabolic mirror. From Astra 19.2 ° East via Eutelsat 16 ° East, Hotbird 13 ° East, Eutelsat 10 ° East, Astra 4 5 ° East to Thor / Intelsat707 on 1 ° West, three satellite positions are fed into a house system via a multi-switch and another three LNBs supply a single recipient. This "Balkan solution" means that all programs from Bulgaria available via satellite are received on the single receiver.
There are also mirrors that are shaped in such a way that instead of a focal point, there is a focal line. With a 55 cm wavefrontier toroidal antenna, approx. 40 ° of the satellite sky can be covered. The reception power for each satellite should correspond approximately to a 60 cm dish (35.7 dB antenna gain ). If 3 ° satellite spacing is desired, there are also larger antennas, e.g. B. the T90, which has a gain of about 39.7 dB gain. With special LNBs, distances of 2 ° can then also be achieved for some satellite positions.
Since the complete conversion to digital transmission , many of the satellites have lost their importance for private television reception. If you do not want to receive very special exotic programs, two to a maximum of four satellite positions are usually sufficient.
Further meaning
In addition, multifeed refers to the switching of channels with several option channels associated with an option button, for example ESPN (American sports channel), Sky Sports Portal, Sky Select and many more.
See also
Individual evidence
- ↑ Mounting plate for up to three satellite positions
- ↑ EMP-Centauri Profi Line MS33 / 12PIU-6 with 32 IF levels for 12 participants
- ↑ see satellite allocation with programs on www.lyngsat.com