Rev. 2 | |
Front Panel Menus | CD/CIM550.IOM |
(Transmit an alternating 1,0,1,0 pattern) This is a test mode which | |
| forces the modulator to transmit a carrier modulated with an |
| alternating 1,0,1,0 pattern, at the currently selected symbol rate. This |
| causes two discrete spectral lines to appear, spaced at +/- half the |
| symbol rate, about the carrier frequency. This mode is used to check |
| the carrier suppression of the Modulator. |
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IF LOOP | (IF Loopback) This test mode invokes an internal IF loop. This is a |
| particularly useful feature, as it permits the user to perform a quick |
| diagnostic test without having to disturb external cabling. |
| Furthermore, all of the receive configuration parameters are |
| temporarily changed to match those of the transmit side. When |
| NORMAL is again selected, all of the previous values are restored. |
DIG LOOP | (Digital Loopback) This test mode invokes a digital loopback, which |
| loops data at the output of the digital FIR filter on the transmit side, |
| back into the Viterbi decoder on the receive side. This tests all of the |
| interface, transmit baseband circuits, FEC encoder, FEC decoder, |
| and buffer. |
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I/O LOOP | (Inward/Outward loopback) This test mode invokes two distinct |
| loopbacks. The first of these is the inward loop, which takes data |
| being received from the satellite direction, and passes it directly to the |
| modulator. Simultaneously, the outward loop is invoked, whereby data |
| being fed to the transmit data interface is routed directly back out of |
| the receive data interface. |
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The three loopback modes are illustrated in the following figure.
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