ASM 988A – Manual
9
MODULATION FORMAT
The Modulation Format menus allow changes to different modulation modes supported
by the ASM 988A. When this menu is selected, several options can be viewed by using
the Up/Down arrow keys to scroll through the settings.
The Modulation menu allows DVB QPSK, 8-PSK mode, Advanced QPSK, Adv 16-
QAM and DSS QPSK modes. All of these modes are available using Turbo Coded
forward error correction. The QPSK DVB mode also allows for legacy DVB FEC
support as well. The modulation mode and code rates are given together. In all, there are
17 combinations of modes and associated code rates that can be chosen between. To
change the modulation mode and code rate, press ENTER to edit, use the Up/Down
arrow keys to select a rate and mode, and press ENTER to save.
FEC FEC FEC FEC FEC
DVB QPSK 1/2 2/3 3/4 5/6 7/8
ADV QPSK 1/4 1/2 3/4
DSS QPSK 1/2 2/3 6/7
8SPK 2/3 3/4 (2.05) 3/4 (2.10) 5/6 8/9
Adv 16 QAM 3/4
This table is a summary of the different modulation modes and FEC available.
IF FREQUENCY
The Center Frequency of the modulated signal is centered about 70,000,000Hz. The
center frequency can be changed through the menu within a band of 50MHz to 90MHz,
in 1Hz increments. However, this signal is still restricted to a 40MHz window, where the
cutoff for the low end of the band is fixed at 50MHz and the upper end is fixed at
90MHz. To change the IF Frequency, press ENTER, using the Up/Down arrow keys, set
the new IF Frequency and save by pressing ENTER again.
SYMBOL RATE (SPS)
The Symbol Rate menu is the baud rate of the modulated signal, given in
symbols/second. This, along with the rolloff of the channel, Alpha, gives the overall
bandwidth of the channel. This parameter is also directly related to the payload rate.
Changes to either parameter will affect the other. To edit the Symbol Rate, press ENTER
to edit, using the Left/Right arrow keys to select a digit to modify and the Up/Down
arrow keys to “thumbwheel” through digits, then press ENTER to save.
PAYLOAD RATE (bits/sec)
The Payload Rate is the amount of data that is transmitted through the channel, given in
bits/second. This is related to the Symbol Rate through the Modulation Format and
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