RSM1 Remote Spectrum Monitor System

The RSM1 remote spectrum analyzer was originally designed for monitoring IF feeds at satellite ground stations, however it can be adapted for many other remote spectrum monitoring functions. For off-air monitoring, preamplifiers/downconverters and antennas can also be provided to form a self-contained system.

The basic RSM1 remote spectrum analyser allows several IF feeds at a satellite ground station to be monitored over a TCP/IP network. It consists of a server, installed in the ground station, and client software that will run under Windows or Unix/X11.

Server

The server comprises:

• A standard spectrum analyser. Currently HP856x and E440x analysers are supported. Others can be added to the list of supported analyzers as required.
• One or more cascadeable 8-way IF/RF switches (Giastar IFS1) to provide IF feed selection.
• A system controller (Giastar RPC1).

The system controller's operating system is Linux, and all RSM1 software except the GPIB (HPIB) device driver is programmed in Python.

The modular system has been designed for easy modification and customisation, so that application-specific functions, or support for other devices (e.g. vector signal analysers) may easily be added.

The server can be controlled and interrogated over TCP/IP using a standard text-mode telnet or SSH (Secure Shell) client if required, however the graphical client program provides more features:

Client

The graphical client software uses a cross-platform language (Python) and GUI libraries, and can therefore be ported to various operating systems. Currently Windows 98/NT/2000/XP and Unix/Linux are supported. Mac OSX clients can be provided if required. The client software may be downloaded from the server either via a web browser or ftp client. When used over untrusted networks security can be tightened by allowing only https and SSH (Secure Shell) connections.

At first sight the client screen looks like little more than a duplication of the spectrum analyser display, however the displayed image has been recreated "from scratch" from the raw data and there is a lot going on behind the scenes:

• Frequency and level are converted from monitored IF values (not particularly useful) to the corresponding RF values. Frequency may be entered as uplink or downlink, L-band or C-band, and the necessary conversions are done transparently. Alternatively, channel numbers can be entered instead of frequencies.
• Span, bandwidth etc can be automatically set according to the signal type being examined, decreasing the risk of inappropriate analyser parameters giving misleading trace displays.
• Signal C/No levels are automatically calculated and displayed (top right).
• The currently selected IF signal is shown on the display (bottom left).
• Several concurrent traces are displayed, expanding the display features of the basic analyser.

This image shows the system control menu. Many of the menu items are self-explanatory, except for "Auto-cal":

The Auto Calibrate function provides continuous level calibration of the entire system, to give accurate level measurements by compensating for gain drift throughout the space and ground segments. This is done by using alternate analyser sweeps to monitor the main signal and a calibration pilot signal. The calibration sweep is done in the background and is not displayed. The trace and associated measurements are adjusted to compensate for errors.

This image shows the trace (display) options. Several traces may be displayed:

• The main trace (yellow): Updated once per sweep.
• Max hold trace (red).
• Memory trace (blue). This may either be recalled from disk or be a "frozen" main trace. Whenever "Freeze" is selected the main trace is transferred to the memory trace. This is useful for comparison purposes.

Other application-specific options may be added if required, including:

• Waterfall display
• Superposition of forward and return signals
• Out-of-limits alarm. If a signal falls outside specified amplitude or frequency limits an alarm can be raised, via:
  • visual/audible alarm
  • email
  • SMS
  • voice message via phone or radio
• Automatic switch-over to backup equipment in the event of an out-of-limits alarm.

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