Rf Modulators; Rf Demodulators; Diversity (Option); Start-Up Procedures - Radyne MM200 Installation And Operation Manual

Mm200 high speed microwave modem

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MM200 High-Speed Microwave Modem

Data is always evenly divided between the number of channels selected i.e. each RF modulator

runs at the same rate.

3.1.3 RF Modulators

The number of active modulators (up to the maximum number installed in the chassis, from 1 to

4) is determined by front panel selection in which case any unused modulator is "parked" or

turned off. Each modulator is capable of modulating a carrier between 50 and 90 MHz with QAM

4,16,32,64,128 or 256 (optional). The range of symbol rates per modulator is 3.5 to 7 Msps giving

a total range of 3.5 to 28 Msps. The four outputs are combined to a single IF output. Output

power is adjusted by a 1 dB step attenuator.

The RF Demodulators mirror the RF Modulators in their specifications. The receive signal is split

four ways each going to an independent demodulator. Again, the number of demodulators (up to

the maximum number installed in the chassis, from 1 to 4) can be set from the front panel. The

Modulator and Demodulator setup must be identical for the signal to pass.

Each demodulator has a powerful digital equalizer to remove multipath and other signal

degradations.

The Demux removes the overhead and sends the appropriate data to the appropriate interface as

identified by its unique PID (Packet Identifier). The Tx interface must match the Rx interface.

When the system requires Diversity such as Space Diversity or Frequency Diversity, the receiving

site must have two independent receive signals. Each of the two MM200 chassis are required to

be optioned with a minimum of identical receivers (number of RF channels) and a diversity card.

Only one chassis needs to be optioned with interfaces if no equipment redundancy is required.

The transmit side of both chassis are completely independent from diversity operation and can

therefore be optioned in any configuration.

Data from the demux is sent to the diversity card where it is buffered and aligned in time with the

signal received from the other diversity card. Both these signals appear at the hitless switch.

Error information from all receivers is sent to the hitless switch driver where a decision is made as

to which stream to output. The output will be error-free providing one of the demodulator chassis

is receiving an error-free signal. If both chassis are receiving errored signals, the output can still

be error-free providing errors occur in different Reed-Solomon packets.

Both diversity cards send and receive data to and from the other unit, so both chassis will output

the best data stream of the two units.

Turn the unit on.

Set Tx Power to '–10 dBm'.

Set the Demodulator Attenuation to '20 dB'.

Under the Mod/Demod Test, set PRBS to '–2e23M'.

Connect IF Out to IF In via a 75Ω Coax Cable.

TM086 - Rev. 4.1

Theory of Operation

3-3

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