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QMultiFlex-400™ Installation and Operating Handbook
8.3.4.1 Enable Hub Outbound Carrier and Canceller
Enable the Hub Modem's carrier. The remote Modem demodulators will lock, at the same
time the hub multi-demodulators will unlock. Configure the Hub Canceller: Enable the Hub
Canceller: (Edit > Paired Carrier)
Heading
Parameter
Paired Carrier
Paired Carrier Enable
Earth station longitude
Earth station latitude
Min round-trip delay
Max round-trip delay
8.3.4.2 Hub Canceller Configuration
Round Trip Delay: The configuration of the Hub canceller round trip delay depends on
whether the Round-Trip Delay (RTD) from the hub to the satellite is known or not. If you
already know the RTD, simply set this to `Set delay` and enter an RTD sweep range into
the canceller. This delay range needs to be wide enough to encompass the actual RTD
swing, but not so wide that the canceller takes an extended time period to acquire. So, if
the mean RTD is known, enter a minimum delay of 0.5ms below the mean and a maximum
delay of 0.5ms above the mean.
Set Location: If you don't know what the RTD is, specify the geographical location of the
Hub-station and the satellite longitude. An estimate of the RTD will be displayed given
your satellite and ground-station co-ordinates. The Hub Canceller is then able to derive a
suitable delay sweep range for the canceller to operate.
Use GPS: Alternatively, if the modem is connected to a GPS tracker via its rear-panel serial
port, the station co-ordinates can be read by the modem from the GPS serial "NMEA"
messages. With the GPS geo-location data, together with the satellite longitude entered by
the user, the modem can automatically program the canceller with a suitable delay sweep
range. The use of a GPS tracker is sometimes used in Comms-On-The-Move (COTM)
mobile systems or terminals. As the terminal moves and its geo-location changes, the
modem will update the minimum and maximum delay sweep range settings for the
canceller automatically.
In addition to the Round-Trip Delay entries covered above, there is a fourth method, where
the Hub canceller is set to `Auto Acquire`. Once enabled, this involves the Hub canceller
finding out for itself what the RTD is for the looped satellite communications path, without
any user involvement. Auto-acquisition may take a few seconds longer compared to the
above methods where a narrow delay sweep range is defined. When `Auto-Acquire` is
selected, it will grey out the other delay methods and prevent them from being selected.
The control page has an extra element over the standard Paired Carrier of SCPC Modems,
termed `Rx Carrier Frequency`. Ascertain the centre frequency of the returned echo and
enter this in the Rx Carrier Frequency field (the carriers overlap on satellite, so the returned
echo frequency may be different to the configured Modem Tx frequency!).
When the method for establishing the round-trip delay is set to Set location then the satellite
delay calculated by the modem will be displayed. This can be used to reduce the
Round-trip delay
Satellite longitude
Table 8-5 – Hub Canceller Menus
Options
On / Off
Set Location/delay/GPS
-180 to +180
-180 to +180
-90 to +90
0 - 300ms
0 - 300ms
8-12
Configuration
On
Set delay
N/A
N/A
N/A
(0.01ms for Bench test)
(0.05ms for Bench test)
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