Receiver Will Not Acquire Signal - Wegener DR95 Instruction Manual

4. Receiver Will Not Acquire Signal

a. Check that the receiver is set to receive correct frequency. "Desired frequency" at top of
terminal's 'RC' response screen is the satellite downlink frequency. THIS SHOULD
BE EXACTLY EQUAL TO THE ROTARY SWITCH SETTING ON THAT RF
CHANNEL'S ID96 CARRIER-IDENTIFIER AT THE TRANSMIT SYSTEM.
b. The "Desired Frequency" displayed on the terminal may not be correct because the
receiver has timed out into either a (Table) SEARCH or HEADER-search mode and is
looking for other carriers in its pre-loaded Search Table. Set MODE switch 8 down and
cycle the AC line power to the receiver. Then issue a 'PERM' frequency command for
the correct frequency, allowing a full minute for acquisition to take place.
c. If the receiver still does not acquire, check the signal path from the antenna LNB. If the
receiver's AGC LED remains lit continuously while the receiver searches, there probably
is a very low noise floor being input. (In practical downlinks, the LNB would output
noise at a level high enough to turn off this LED.) If the cabling looks OK, check that the
receiver is putting the >+15VDC on the RF INPUT connector's center-pin (if applicable)
and that that voltage is being passed through appropriate DC power-pass devices all the
way to the LNB.
d. On the response screen for 'RC P,' note the "LNB LO Frequency." The difference
between that and "Desired Frequency" is the expected L-band input frequency. Verify
that this is the frequency available at the receiver's RF input. Use a calibrated spectrum
analyzer to check the frequency and occupied bandwidth of the signal. This signal must
be within ± 1 MHz of where the receiver expects to see it. The occupied bandwidth (6
dB) of the signal should be about 2.5 times the MPEG-encoded data-rate (see procedure
1, steps i and n). If it isn't, you may be looking at someone else's signal, or the transmit
and receive systems are at incompatible data-rates.
e. If receiver still does not acquire, check the response screen to the 'RC' command for
"Acquisition Difficulties." If no Acquisition Difficulties are given, proceed to step l (L).
If only "No MPEG," proceed to step k. If it reads "Incorrect Tag," re-verify the check
performed in step a above because the Carrier-Identifier at the transmit site and the
receiver are not in EXACT agreement on the receive frequency.
f. If the Acquisition Difficulties are "No Tag," this often indicates some failure or
misconnection of the ID96 Carrier-Identifier in the transmit system. It also could indicate
that the receiver's tag-reading routine has been disabled for testing and never re-enabled.
First check the receiver by cycling the AC line power and observing the initial screen. If
MPEG or TAG are disabled, it will be so indicated. They will need to be re-enabled by
Wegener Communications personnel. If it is possible to establish a modem link from the
receiver back to the factory, a service return may be avoided.
g. If the receiver settings are OK, try substituting a spare receiver if possible. If the same
symptoms occur, the transmit system must be the next suspect.
h. To troubleshoot the transmit system, it is again recommended that the Transmit System
Checklist be performed. If OK, check to see if the ID96 Carrier-Identifier shelf is getting
DR95/DR96-001 4-6