Teledyne Q-Lite, Инструкция по установке и эксплуатации, Страница: 113 / 242

Q-Lite Satellite Modem Installation and Operating Handbook
6-80
7. Switch the second carrier off.
To avoid non-linear distortion, ensure adequate HPA back-off when
using multiple carriers through a single amplifier, particularly with
higher order modulations when testing at a single site.
8. At each modem, set either location information or, alternatively, the
round trip delay to satellite (via the Round-trip delay setting on the Edit-
>Paired Carrier menu). 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 (via the Paired Carrier
enable setting on the Edit->Paired Carrier menu). Its demodulator
should lock (Rx traffic LED should go green).
12. Enable Paired Carrier™ in the second modem (via the Paired Carrier
enable
setting on the
Edit->Paired Carrier
menu). 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