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System Enhancements - Optional Design Features

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    Posted: 07/August/2015 at 23:00
System Enhancements - Optional Design Features
 
In these tutorials we will look at the various component parts that make up a satellite ground station and the typical practices that engineers employ during satellite ground station engineering projects.
 

System Enhancements

Matrix Switch
As mentioned in the IF Equipment Tutorial, a matrix switch is simply a patching system which is used at IF frequencies to connect modems to converters in both transmit and receive paths. It is essentially a set of combiners and splitters with switches that connect the inputs to the outputs in almost any combination.

These units have replaced traditional patch bays which required human interaction to connect modems to converters using patch cables and patch panels. Due to repeated use the cables became damaged and the connectors on the panels also suffered resulting in system faults which then required expensive repair. Matrix switches can be automated and are designed to handle repeated switching often with redundancy built-in.

Redundancy
In order to safeguard against system failures and loss of communications, the ground station should be designed to include redundancy. The most basic redundancy is 1 to 1 in which there is one back up unit for one operational unit. In the case of HPAs and LNAs this is automatically switched in to take the place of a failed operational HPA or LNA.

For dual polarisation systems there are two transmit paths so either a dual 1:1 redundant system is required which uses 4 HPAs and LNAs or a 2:1 system can be used that has one back up switchable between either of the other two units. There are also more redundancy systems such as 3:1 or 4:1 dependant on the number of signal paths.


Carrier Spectrum Monitoring (CSM) or Carrier Monitoring System (CMS)
When operating a large ground station or a number of large ground stations it is often useful to have a semi-automated monitoring system that keeps watch over the RF transmissions. Just like the M&C system watches over the equipment, a carrier monitoring system watches the RF spectrum.

A typical CSM consists of an L-Band IF Switch which is connected to a standard L-Band Spectrum Analyser. Both devices are connected to the CSM computer via an Ethernet IP network. The operator can view any spectrum by selecting carriers and transponders from a drop down list. Alarms are initiated when any abnormal condition arises:


• Occupied Bandwidth
• Center Frequency
• EIRP (RF Power) and C/No outside of a certain tolerance
• Spectrum shape alarm which is based on the shape of the displayed trace


There are typically two types of automatic monitoring functions:

The first is the "Spectrum mask" as it is often called, or the "Reference Trace monitoring".
The second is parameter monitoring.

Reference Trace monitoring is the simplest method. This compares the displayed trace to a stored reference that contains upper and lower trace limits.

Parameter monitoring provides a comprehensive comparison of the measurement parameters to the defined limits.

This concludes Course 8 of the Tutorials.



Edited by Satcoms UK - 30/August/2015 at 22:45
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