Comtech EF Data CDM-570A - Manual (Page 152)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Front Panel Operation Revision 2
6–48
6.3.4 SELECT: TEST
TEST: Mode BERT
Use the ◄ ► arrow keys to select Mode or BERT. Press ENTER.
6.3.4.1 TEST: Mode
TEST: Norm IF ↓ Dig ↓ I/O ↓
RF ↓ Tx-CW Tx-1,0(◄ ►,ENT)
Use this menu branch to execute a variety of test modes. Use the ◄ ► arrow keys to select a
Test Mode. Press ENTER.
Mode Description
Norm
(Normal) This clears any test modes or loopbacks, and places the modem back into an operational
state.
IF ↓
(IF Loopback) This test mode invokes an internal IF loop. This is a particularly useful feature, as it is
used 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. During an
IF Loop, the Tx carrier continues to be transmitted. See Figure 6-3.
When Norm is again selected, all previous values are restored.
Dig ↓
(Digital Loopback) This test mode invokes a digital loopback, which loops data at the output of the
framer/scrambler on the transmit side and back into the deframer/descrambler on the receive side. If
concatenated Reed-Solomon FEC is being used, this is also included in the digital loop. See Figure 6-3.
I/O ↓
(Inward/Outward loopback) This test mode invokes two distinct loopbacks:
• The Inward Loop 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. See Figure 6-3.
RF ↓
(RF Loopback) Useful for performing a satellite loopback, this test mode is almost identical to the IF
loop mode: All receive configuration parameters are temporarily changed to match those of the transmit
side; however, no internal connection is made.
When Norm is again selected, all previous values are restored.
TX-CW (Transmit CW) Used for measuring phase noise, this test mode forces the modulator to transmit a pure
carrier (unmodulated).
TX-1,0
(Transmit an alternating 1,0,1,0 pattern) Used to check the carrier suppression of the Modulator. This
test mode 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.
If OQPSK is selected as the modulation type, the test produces a spectral pattern suitable for the
measurement of SSB rejection – useful in determining the phase and amplitude accuracy of the
modulator.