Quantum and Evolution Series Installation and Operating Handbook
7-102
8. At each modem, set either location information or, alternatively, the
round trip delay to satellite (Main, 2:Edit, 3:Rx, 7:Carrier, 4:Advanced,
2:PCMA, 2: Round Trip Delay). If location information is entered for the
modem position then the satellite delay will be calculated automatically.
To minimise acquisition time when using a round trip delay, the delay
should be specified to within ±1ms of the nominal value that you have
calculated.
9. Enable the Tx carrier in the first modem. Both demodulators should
lock (Rx traffic LED should go green).
10. Enable the Tx carrier in the second modem. Both demodulators should
go out of lock (Rx traffic LED should go out). Please note: the combined
carrier power will increase by 3dB when the second carrier is enabled.
11. Enable
Paired Carrier
in the first modem (Main, 2:Edit, 3:Rx, 7:Carrier,
4:Advanced, 2:PCMA, 1:Enable and set to ON). Its demodulator should
lock (Rx traffic LED should go green).
12. Enable
Paired Carrier
in the second modem (Main, 2:Edit, 3:Rx,
7:Carrier, 4:Advanced, 2:PCMA, 1:Enable and set to ON). Its
demodulator should also lock (Rx traffic LED should go green).
13. Enable the BER test and check for data transparency in both directions.
Inject errors via the BER testers in both directions and ensure they are
received correctly.
14. If the modems do not lock or are not data transparent then
•
Ensure there is no spectral inversion in the RF chain. If there is,
then this must be corrected by re-inverting it for
Paired Carrier
operation to work.
•
Check the modem/satellite location information or round trip
time that has been set in each modem. The range entered for
the round trip time must cover the actual distance to the
satellite. Try widening out the round trip delay to ensure that it
definitely covers the actual time delay to satellite. Try switching
from location to round trip delay or vice versa.
•
Switch
Paired Carrier
off and on again in each modem (to
counter the possibility of a false lock).
•
If this does not work then switch the carrier off and on again in
each modem.
•
Check the receive signal level and Eb/No are correct.
•
Check the spectrum and constellation for signs of signal
degradation such as noise or interference.
•
Otherwise check the general modem settings for correct
configuration and overlap of the two carriers (note that there are
restrictions on the supported level of power asymmetry and
symbol rate asymmetry).
15. If the modems take a long time to lock then
•
Narrow the difference between the minimum and maximum
round trip delay times (if these are being used) to minimise the
uncertainty in the range to the satellite (Main, 2:Edit, 3:Rx,
7:Carrier, 4:Advanced, 2:PCMA, 2: Round Trip Delay). This has
a significant effect on acquisition time. If using a round trip delay
then try switching to using location information.
•
Check for signs of signal degradation such as poor Eb/No
values or poor spectrum and constellation.
