Mocomtech CDM-QX - Manual (Page 79)

CDM-Qx/QxL Multi-Channel Satellite Modem with DoubleTalk™ Carrier-in-Carrier® Revision 7
Front Panel Operation MN/CDMQX.IOM
5–13
5.4.2 CONFIG: Tx (Transmit)
Tx: FEC Mod Code Data Freq
On/Off Pwr Scram Clk Inv Txα
Select FEC, Mod, Code, Data, Freq, On/Off, Pwr, Scram, Clk, Inv, or Tx α
using the ◄ ►
arrow keys, then press
ENTER
. The user will then be taken to a further submenu. Each selection
is described briefly as follows:
FEC
(Forward Error Correction) This submenu permits the user to select the method of FEC
used for transmission (Viterbi, TPC, etc). FEC type takes the highest configuration priority.
Mod
(Modulation) This submenu permits the user to select the modulation type used for
transmission (BPSK, QPSK, 8-PSK, etc.). The available choice of modulation will depend on
the FEC type chosen.
Code
(FEC Code Rate) This submenu permits the user to select the FEC Code Rate used for
transmission (Rate 1/2, Rate 3/4, etc). The available choice of Code Rate will depend on both
the FEC type and Modulation type selected.
Data
(Data Rate) This submenu permits the user to select the transmit data rate, in steps of 1 bps.
The choice of data rate will depend on the FEC type, Modulation type, and Code Rate
selected.
Freq
(Frequency) This submenu permits the user to select the transmit frequency, from 950 MHz
to 1950 MHz, in steps of 100Hz for L-Band units, or from 50 MHz to 90 MHz and from 100
MHz to 180 MHz for 70/140MHz units.
On/Off This submenu permits the user to control the output state of the transmit carrier.
Pwr
(Output Power level) This submenu permits the user to control the output level of transmit
carrier, either manually, or using the AUPC (Automatic Uplink Power Control) feature.
Scram (Scrambler) This submenu permits the user to select whether or not data scrambling is used.
Clk
(Clock Source) This submenu permits the user to select the clock source for transmission.
This can be from the internal source, from an external source, or from the distant-end of the
satellite link (loop timed).
Inv
(Inversion) This submenu permits the user to invert the sense of the transmitted spectrum,
or to invert the sense of the transmitted baseband data or data clock
Tx
α
(
α-Factor) This permits the user to select the modulator’s roll-off factor either 20% or 35%.
The FEC type takes the highest configuration priority, and the selection
here depends on what, if any, optional plug-in Codecs are installed. The
choice of FEC type then determines what modulation types, code rates,
and data rates are available. The order of hierarchy is therefore:
FEC type ► Modulation type ► Code Rate ► Data Rate
(Highest) (Lowest)
If the user changes a parameter within this hierarchy, the other parameters may become invalid.
In this case, the software will change those other parameters, in order to maintain a valid
configuration at all times.
Example: Suppose the user has selected Viterbi + Reed Solomon, QPSK, Rate 1/2. Now, the
user changes the modulation type from QPSK to 16-QAM. In this case, Rate 1/2 is no longer a
valid code rate, and so it will be automatically changed to the nearest valid code rate (Rate 3/4).
Detailed descriptions for each of the Tx configuration submenus follow.
IMPORTANT