Taal: [nl]

Cascade operation can be studied in the four-satellite example system to the right. A program is received from the fourth antenna, which is in high band and vertical. This results in the following:

Option = 1
Position = 1
Polarization =0
Band = 1

Command 38 should be used for control. Its data byte is comprised of the first nibble to erase the previous condition byte and the second nibble, which forms the new condition bits. When the second half byte contains the complete IF-path description, all "old" condition bits can be erased with the nibble byte for simplification. The nibble becomes "F".

The example bits for setting are put together in decreasing order (1101) result in the nibble "D". "FD" results as a data byte.

Let’s say we are on antenna 2 and want to switch to antenna 4, the receiver sends the DiSEqC message E0 10 38 FD, which is received by all components in the path to LNB 2.

LNB 2 and the left universal relay can respond to the message if need be, but the bottom relay - which is configured as an option switch and therefore only evaluates the option bit - switches the IF path to the right relay.

Since the right universal relay (configured as position changeover switch) was only switched to the IF path after the DiSEqC message, it is still in its initial position. The path leads therefore to LNB 3.

The receiver must now send the DiSEqC message a second time. This is simultaneously received by the bottom and right universal relay, as well as by LNB 3. The bottom universal relay again finds the option bit set and keeps its switch position. The right relay receives the position bit and switches to LNB 4. After the second DiSEqC message the remote voltage is switched over and the 22kHz audio tone is switched on (for high band selection, as in the example). With DiSEqC LNBs, the DiSEqC message is sent a third time before that.

Receivers with the DiSEqC logo must be able to repeat the messages. The number of repeats often can be set in the installation menu of the satellite receiver and must at least equal the number of cascading levels, but too many repeats slow down switching.

over de inhoudsopgavevorige paginavolgende pagina

Pagina 24 / 29

  Printversie

Naar boven