Technical information

User Interfaces MM200 High-Speed Microwave Modem
4-6 TM086 - Rev. 4.1
4.3.3 DEMODULATOR (menu)
The Demodulator Menu Screens are listed below:
Screen Name Selections and Descriptions L2
FREQUENCY (Hz)
{50 – 90 MHz}
Displays the current center band of the
operating frequency width.
RW
CHANNELS
{Auto, 1 – 4, Debug}
Controls the number of channel cards
where 0 = auto, and 1 – 4 = the number of
cards. Increase this number for better
performance. Lower this number for
better bandwidth efficiency.
RW
SYMB RATE (SPS) {3.5 – 28 Msps}
Controls the total Symbol Rate.
RO
DEMODULATION {QAM4, QAM16, QAM32, QAM64,
QAM128, QAM256}
Displays the current Demodulation
Scheme.
RO
BANDWIDTH (Hz)
Displays the frequency difference between
the highest channel’s upper 3-dB point
and the lowest channel’s lower 3-dB point.
RW
UTILIZATION (%)
Displays the percentage of the data being
transferred that is being used by the
selected interfaces. Must be less than
100%. Maximize this number for best
bandwidth efficiency by lowering the
symbol rate, QAM Mode, or the number of
channels.
RO
MAX PAYLOAD (Hz)
Displays the maximum total data rate that
is useable for the current settings.
RO
SPECTRUM
{Normal, Inverted}
RW
ATTENUATION
{0 - 31}
Sets the Demodulator Input IF Attenuator
in 1 dB steps.
RW
ACQUISITION (menu):
The Demodulator Acquisition Frequency
range can be set by the user. This is
required at higher QAM rates when using
radios with significant frequency drift. As
QAM rates increase, the ability of the
receiver to acquire to a signal that is offset
from the programmed demodulator
frequency is reduced. At QAM256 the
acquisition window can be as low as ± 50
kHz. Yet at QAM4, the window can be
over ± 1 MHz. This range can be further
reduced by noise or degraded receive
signals.
When trying to acquire a signal, the
MM200 follows this procedure:
1. Try to acquire at the Demodulator
Programmed Frequency.
2. Continue to try to acquire for the length