Introduction

Signal Surveyor 4D is high-speed signal monitoring software designed to find and collect information on wireless communications. Surveyor 4D, when combined with the N6841A RF sensor, M9391A vector signal analyzer (VSA), and M9393A VSA creates an automated spectrum monitoring system for signal search and survey functions. It covers the spectrum from 100 kHz to 50 GHz (depending on the hardware configured) with sweep rates up to 4 GHz per second across multiple antennas. The Surveyor 4D has all the basic capabilities including energy detection and alarm processing and user libraries to enhance signal characterization and identification. It also includes a well-developed interface to the PostgreSQL database and signal external triggering schemes and recording options. It can also be used as a development platform for creating new User-defined libraries. A brief introduction of the N6841A RF sensor is presented in this link [1].

Key Features

• High-speed, high-resolution spectrum search

• Automated signal survey and classification tools

• Powerful triggering and masking functions

• Scheduled alarm functions and flexible tasking

• SQL database for long-term logging and analysis

• Built-in spectrum recorder

• Flexible multi-band search modes

• Geolocation – Automatic tasking of RF signal location sub-systems

• ITU-RSM.1600 Technical identification compliance

• IQ capture and recording of RF signals

Applications

• Spectrum monitoring and logging

• Spectrum management

• Interference detection and location

• Band clearing

• Signal development

• RF Survey

• Special signal intercept and collection

• Satellite downlink monitoring

As shown in the diagram below, Surveyor 4D works by first receiving high-resolution, high-speed spectral data from the hardware. RF signals are separated from the noise by using configurable energy detection and thresholds. Next, the parametric data of the RF signals are measured and stored in the energy history database. Specific parametric information can be used to trigger alarms, and actions can be taken through the defined alarm tasks.

Hardware Description

For signal surveying applications requiring a small, rugged time-enabled receiver, select the N6841A RF sensor which operates standalone or synchronously with other RF sensors in fixed, temporary, and mobile deployments capable of making TDOA emitter location measurements.

For applications requiring wider bandwidths, higher search speed, or 50 GHz frequency coverage, select the M9391A (or M9393A) PXI module.

For applications requiring portability and extended frequency range, select from the FieldFox handheld RF analyzers. Hence, it is recommended to select hardware that will best meet the application requirements. Hereinafter, we will consider a Signal Surveyor 4D combined with an  N6841A RF sensor and report some key hardware specifications below.

Specifications: 

• Frequency range: 20 MHz to 6 GHz

• Memory: 1 GB

• Sweep speed: 4 GHz/sec

• Noise figure: 13 to 26 dB

• Digital Downconverter Channels: 8

• Streaming bandwidth: FFT = 20 MHz, I/Q = 1.56 MHz

Surveyor 4D Software Description

Energy Detection

As stated earlier, Surveyor 4D conducts high-speed, high-resolution RF searches across single or multiple radio bands processing energy that meets detection criteria. Detecting energy is a core feature of the Surveyor 4D software. A spectral threshold line is required for energy detection, and Surveyor 4D provides a variety of options, including Level, Auto, Environmental, Point Average, Segment Average, and File. The ability to choose energy thresholds is particularly useful for dealing with a variety of circumstances that arise in real-world spectral events [1]. 

When the energy threshold is exceeded, an entry is made into the Energy History Database (EHD).  The EHD is used as an interim repository where intercept data is further processed and refined through filtering and alarms. Each entry of EHD contains over 20 precisely measured parameters based on signal externals associated with the detected energy. Parameters include, but are not limited to frequency, bandwidth, amplitude, power, field strength, duration, and occupancy [1].

Energy History Filters

Surveyor 4D can apply Energy History Pre- and Post-Filters designed to restrict or open the flow of detected energy data into, or out of, the EHD. For example, the Post-Filter “Age” removes entries after the energy drops below the threshold for a user-defined number of seconds. The most commonly used Pre-Filter is the Universal Signal Detector (USD) which has several key signal characteristics that can be used independently or together to perform signal isolation and classification [1].

Energy Alarms

An Energy Alarm is a system-level trigger. The alarm criteria are based on one or more of the parametric data elements collected and stored in the EHD. These parameters can be used independently or together by an Alarm to isolate a spectral event of interest. When the Alarm triggers, one or more actions (referred to as “Tasks”) are executed. These tasks can include:

• Handoff the frequency to an external receiver which could demodulate the signal and play or record the audio.

• Take a frequency Snapshot of a user-defined portion of the spectrum.

• Send an IQ time-series record of the energy to the Modulation Recognition algorithm.

• Give the operator a visual indication on the computer screen that the alarm was tripped.

• Take an IQ time-series recording on the frequency that tripped the alarm with a user-specified bandwidth and length.

• Task a network of N6841A RF sensors to locate the emitter that tripped the alarm.

• Give the operator an audible indication that the alarm tripped.

• Add/Remove the frequency that tripped the alarm to/from one of ten configurable frequency lists.

• Custom, user-defined alarms can be created by Keysight or trained partners for special cases. For example, send an email or call a pager.

Signal Database And Reporting

Some Alarm tasks will generate an entry in the signal Database (SDB). The SDB contains information from signal processing tasks such as Universal Signal Detection (USD), Modulation Recognition (MR1), Direction-Finding (DF), emitter Location (GEO), Time or Frequency recording.

Surveyor 4D Tools

Surveyor 4D Spectrum Record and Playback Tool

The spectrum record and playback tool can be loaded as part of the N6820ES extensions and requires no option or license. It provides a record and playback feature for Surveyor 4D’s high-speed spectrum trace data. Recorded files include sequential, time-stamped spectrum traces acquired in either swept or tuner-locked modes. The record and playback feature is ideal for interference and survey applications involving short-duration transmissions. Alarm tasks can be used to start or stop the spectrum recording.

SnapView Software

The SnapView software loads with Surveyor 4D software and enables playback of IQ and Frequency snapshot recordings. SnapView provides a quick and easy way to evaluate time-varying characteristics of a signal, with the spectrum, or real/imaginary time-series views.

Spectrum Survey Tool

The Survey function collects and exports all system findings, including Energy History and Signal Databases, to a format that can be prioritized, sorted, and filtered in Microsoft Excel. With one click, create a full survey report in Microsoft Excel with Surveyor 4D's Spectrum survey tool.

PostgreSQL Database and SQL Visualizer Tool

Surveyor 4D’s integrated PostgreSQL database enables users to understand trends and changes in spectrum use. The SQL visualizer tool enables the creation of plots, charts, graphs, and tables using the spectrum data over long periods of time.

Surveyor 4D Options

User Programming (Option ASD)

Option ASD provides documentation and libraries to customize the Surveyor 4D graphical user interface, such as custom controls, menus, and user panes. Custom energy features, filters, and alarm tasks can also be created. The ASD option requires training and consulting services to implement successfully [1].

Modulation Recognition (Option MR1)

Option MR1 provides an analysis of signal internals to identify modulation formats, frequency deviation, and symbol rates. It can be used in an automated mode, operating as an Alarm task, or in a manual mode, operating on live signal energy or previously recorded IQ data [1].

Universal Signal Detection (Option USD)

Option USD comes with a tool that allows you to make your own signal detectors. It divides the RF spectrum into essential external parameters for each energy (bandwidth, frequency, and shape). These parameters are used to extract and categorize signals of interest. There is no need to program. To develop these bespoke signal detectors, a simple graphical user interface is given. A USD narrowband confirmer can also classify a signal further depending on internal factors (modulation recognition, frequency deviation, and symbol rate) [1].

Narrowband Recorder (NBR)

NBR is a standard part of the Surveyor 4D software and requires no special license. NBR enables the recording of up to eight narrowband RF channels simultaneously. In single-channel mode, up to 1.5 MHz bandwidth can be recorded. In multi-channel mode, up to eight 156 kHz bandwidth channels can be recorded [1].

Starting with Surveyor 4D

Click Start > Keysight N6820ES 4.4> N6820ES with RFSensor. You will be prompted to identify the sensor on which to run the software. Use either the IP address or the Sensor Hostname. After entering the IP address and clicking the 'Finished' icon, the default setup of Surveyor 4D will start. If more than one sensor needs to be connected in 1 instance of Surveyor 4D, or a “multi-sensor” configuration, then click the “More” button. Up to 4 sensors can be connected.

Surveyor 4D Main Window

Graphic User Interface Introduction

The Surveyor 4D window is made up of a menu bar (1) and panes (3- 6), as shown in the following image. Panes are added to or removed from the main window with the Display Layout dialog box or the 'View' Menu and may be organized in many ways.

1. The Menu Bar contains the controls for Surveyor 4D.

2. The Tool Bar offers quick access to three of the menus.

3. A Trace Pane displays sweep data as a spectrum, spectrogram, or color spectrogram. Four trace panes are available, and they can be configured independently or coupled with one another.

4. The Frequency List Pane is used to view, create, and modify lists of frequencies for trace grids and alarm criteria.

5. The Signal Database pane displays the results of signal processing.

Other than these, there are several interesting panes such as the Energy History Pane which displays information on the detected energy, and the Signal Database pane which displays the results of signal processing. 

Undocking and Docking Panes

Individual panes in the Surveyor 4D’s main window can be undocked and positioned separately on the display. They can later be re-docked into the main window.

To undock a pane from the main application window, double-click the vertical bar icon (marked below) located at the left of the pane’s Trace Identifier. The application redisplays the pane as a separate window. To re-dock a pane, double-click the vertical bar icon at the far left of the pane’s menu bar. The application replaces the pane in the application’s main window. To close a pane, click on the “X” close icon in the pane’s top right-handed corner.

Tool Bar

The tool bar offers quick access to the features found in the Configure, Search, and Display menus. Any item in the Configure, Search, and Display menus that is accessible (as defined in Menu/Toolbars) has a button in the tool bar.

1. Antenna Configuration

2. RF Sensor setup

3. Handoff Receiver Configuration

4. System Reference

5. PostgreSQL Database Export (separate manual)

6. Search On/Off (turns the sweep on or off)

7. Search Type (general or directed), Sweep Interval, Tuner Lock

8. Search Setup

9. Energy Detection

10. Energy History Filter

11. Alarms Setup

12. Modulation Recognition

13. Display Layout

14. USD

15. Export and View Results

16. Step Icons

Further Resources

1. KeySight Surveyor 4D N6820ES

2. Understanding the Signal Processing Chain: Energy Detection and Databases

3. Techniques for collection and use of Big Data for Spectrum Management

4. Installation Document

5. Universal Signal Detector (USD)

* While using the tool, click on the ‘About’ icon and Help will open. You can search the keyword there and get useful links.

Below, we provide supplementary information in detecting an RF source, modulation recognition, exporting data for post-processing, setting automatic alarms, and use of universal signal detector. For further information about these tools, please consult the corresponding user manuals from Keysight. 

1. Detecting an RF Source

After opening the software, you will see ‘Color Spectrogram’ and ‘Spectrum’. You may adjust the layout depending on your requirements.  One of the features of Surveyor 4D is to detect any nearby RF source. The steps for detection are as follows.

• There are three main parameters to be adjusted:

1. 1. Desired signal strength - The average signal strength has to be checked first. According to that, the range can be adjusted. In the figure above, the rage is set from -169 dBm to -33 dBm. The signal strengths were very low for that particular frequency range.

   2. Frequency Resolution - RF sensors have a frequency range from 20MHz to 6 GHz. It is difficult to detect a signal if the resolution is very low (i.e. the whole range is observed in a small window of a computer). Using the icon mentioned as 2 in the figure, switching between different frequency windows is possible provided you have a high-frequency resolution.

   3. Desired Frequency range - Depending upon the application, the frequency bands are chosen. The starting and stopping frequencies can be set using the icon mentioned as 3 in the figure.

An example snapshot is provided below where the frequency window is from 91 MHz to 92 MHz. If we observe the second window of the figure, the red line is the threshold signal strength which can be adjusted according to the requirement. There are three picks that are greater than the threshold. The marker is pointing at the highest peak. So, there is a transmission at that frequency.

• There are few options to view which are listed below. Two useful windows among them are ‘Energy History’ and ‘Spectrum Database’ for signal detection. Spectrum database gives few important parameters like the timestamp when the signal was detected, frequency, signal duration, bandwidth, etc. Energy history gives all the energies from 20MHz to 6GHz. It also gives the signal amplitudes at every frequency detected. For setting 1.1 or 1.3, you can observe all the signal amplitudes from this window and decide your desired frequency band. Both the windows get updated continuously in real-time.

2. Modulation Recognition

Surveyor 4D also helps to recognize the type of modulation of a particular signal. The steps for checking the modulation type are listed below:

• Note the frequency and the bandwidth of the signal under observation.

• Click on the icon highlighted above.

• A new window will pop-up

• Click on Assign and enter the values of frequency and bandwidth. Click OK. The modulation histogram of the signal is shown in the right window. If you change the number of blocks for deciding the histogram, you will get more accurate results. At any point in time, you can click on Help to get more detailed information. 

• For accurate modulation information, Vector Signal Analyzer software should be used. 

3. Exporting Data for Post-Processing

For further analysis of the energy spectrum, you can export the data in a CSV file where you will get the following columns:

• Frequency

• Bandwidth

• Amplitude (dBm)

• First and last intercept

• First and last Latitude and Longitude (if Geo-location can be possible)

• Duration

If three or more RF sensors are present in the same subnet, then the location of a particular signal can be obtained and viewed in Google Earth because it gives KMZ file also. You can plot the amplitude of all the frequencies along with the locations.

4. Setting Automatic Alarm

The real data collection process takes a lot of patience and effort. To make that process easy, Surveyor 4D has an automatic alarm option. One can set alarm criteria and define the required actions to be taken, the software will do that automatically. I tried a simple example to set an alarm when the energy of the signal will be more than -80dBm. The steps are as follows:

• Click on the Alarm icon. You can use the arrow keys to set the frequency range you want to observe in the spectrogram as well as in the spectrum window.

After clicking the alarm icon the left window (in the below figure) will open. There are already 100 alarms defined but all of them except one are inactive. You need to select one alarm and click on ‘Modify Signal Alarm’.  Then the right window will open where you can define the alarm criteria according to your requirements.  I have defined an energy threshold of -80 dBm. If any detected signal has energy greater than the threshold, the system will note the frequency, timestamp, and add that frequency in the frequency list. 

You can set up all the tasks at the bottom of the window.

• Click ‘Apply’ and ‘OK’. The alarm will start working. The below figures gives the output of my alarm. To see the alarm log, adjust your view by clicking the ‘View’ option from the taskbar. The alarm log has noted all the alarm has been triggered along with the timestamps and frequencies. In the frequency lists, all the frequencies have been listed when the alarm criteria were satisfied. The bottom-most window ‘Signal Database’ gives some extra information like bandwidth, duration, and the path of the snapshot file.

5. Universal Signal Detector

A universal signal detector (USD) automatically identifies signals of interest by operating on the characteristics of RF transmissions. Agilent’s Universal Signal Detection (Option USD) includes a bandwidth filter, a frequency plan, wideband detectors, and narrowband confirmers. These wideband and narrowband technologies are combined to create universal signal detectors that efficiently sift through the crowded spectrum and significantly increase the probability of intercept. As signals of interest are detected, simultaneous gap-free recordings (or data streams) are easily handled by the multiple digital down converters (DDC) and parallel DSPs in the E3238S system. When a new threat emerges you can quickly build a detector from a recording of a new signal without programming. E6820s comes with an in-built USD which is helpful to collect real-time RF signals without setting any parameters. A typical screen of N6820ES with univ sig detector looks like below.

Here all the nearby FM radio station frequencies are clearly visible. In the bottom-most window, the signal database window, the parameters of the detected signals are listed - Frequency, bandwidth, SNR, etc. You can do all the operations that are possible in generalized N6820ES like modulation recognition, setting alarm, etc.

Snapshot Viewer: A user may initially struggle to see the snapshots because they are either .cap or .fss files. KeySight provides a snapshot viewer inside the package of the software. Set an alarm to take a snapshot and you can view it afterward using the snapshot viewer. Click on ‘File’ to open any of the snapshots and you can examine the snapshot in this window.

USD Classifier: This tool helps to differentiate between different USD signals. It gives you the frequency of the signals, bandwidth, type of modulation, frequency spacing, SNR, and symbol rate. 

You can also visualize all the parameters in the below window. It shows the channel allocation (when the channel is assigned and when not). You may assign the frequency you want to observe.