- CRFS – Spectrum Monitoring and Geolocation - https://www.crfs.com -

Angle of Arrival (AoA)/Direction Finding (DF) FAQs

In the case of mountains, can the antenna system be detached to be installed on the reverse slope?2020-06-15T13:25:14+00:00
CRFS has several different models of DF Arrays ranging in size from large to small. While all DF arrays can be relocated, the method of installation will dictate the ease with which an array can be moved to a new location.
What are the reasons for DF inaccuracy in Mountainous Terrain?2020-06-15T13:24:10+00:00
The greatest contributor to errors in such conditions is multipath which can adversely affect the DF accuracy. There are techniques that can be employed to minimize multipath such as moving position, but perhaps the best approach would be to use a different geolocation mode, such as TDOA.
In RFeye Site> Display Geolocation Mode> Elevation Data Enable. Is default topographical data available in Open Street Maps or does the data need to be loaded from another source?2020-06-15T13:23:31+00:00
The topographical data can be SRTM data as supplied by CRFS map servers or LIDAR data that can be loaded by the user.
Can the user include elevation data from LIDAR sources to be used simultaneously with lower resolution elevation data for surrounding areas (e.g. SRTM)?2020-06-15T13:23:00+00:00
Yes, the Rfeye Site software can import and use LIDAR data. It takes the large data files and creates its own elevation map tiles from the data. The LIDAR data will result in far more accurate modeling than the 30 meter SRTM data. Typically to less than 1m.
How accurate is the GPS?2020-06-15T13:22:07+00:00
The standard system uses conventional GPS for both location and timing. Standard GPS accuracy is typically 35-40 ns RMS. If required, an external SyncLink system (proprietary to CRFS) can further improve this to 10 ns accuracy. The system is also capable of accepting external timing references.
Is post-collection DF processing possible with detached, portable systems (e.g. SenS Portable, Stormcase, Backpack)?2020-06-15T13:21:39+00:00
Yes, post processing of synchronized data is possible with CRFS systems.
How do you align the Array to true North?2020-06-15T13:21:04+00:00
The preferred method is to align it mechanically to true North. If this is not possible, any variation between actual and true North can be compensated for using a configuration file setting
Is calibration required on the van or whatever mobile platform is being used? If so, what does that process look like?2020-06-15T13:20:32+00:00
All DF arrays undergo a rigorous calibration process before leaving the factory. When mounted on the vehicle the impact of the vehicle is minimal compared to the environment. Some customers have conducted post installation calibrations and the CRFS system can support this. However, generally environmental factors such as multipath have a greater impact on ultimate system accuracy than the platform if good installation practices are adhered to.
How many lines of bearing can each array generate simultaneously?2020-06-15T13:20:04+00:00
There are no limits applied to the number of LOBs that can be used at one time, however in practical terms, you would likely want to limit this based on the number of PC screens available, processing time spent at each array, network bandwidth, computer specs, etc.
How far off the ground is the system looking and to which altitude?2020-06-15T13:19:33+00:00
The beams from the arrays are formed with a 60-degree beampattern that is symmetrical in azimuth as well as elevation. For systems requiring elevation data at all elevations, 3D TDOA should be used. CRFS simulation tools include terrain.
How does signal duration / integration processing affect AoA accuracy?2020-06-15T13:19:05+00:00
The DF array uses a number of techniques to build up a picture when considering very short amplitude pulses. The array system essentially does not mind if the signal is pulsed or not. The trade-off is for pulsed signals the system will take a number of samples of the pulsed transmitter to form a LOB.
5G plans to develop a higher frequency component running at 86 GHz. Does CRFS plan to field DF equipment covering any part of the spectrum greater than 18 GHz?2020-06-15T13:18:25+00:00
Yes, we currently plan to release a 40 GHz receiver later this year and we will continue to evaluate the need to go higher as technology and market need dictate.
What techniques do the arrays use to generate lines of bearing?2020-06-15T13:17:23+00:00
The DF array uses two different techniques. For signals below 300MHz it uses beam forming techniques with five omni-directional antennas. Above 300Mhz, it relies on antenna patterns to form the beams and processing from there on in to create LOB. Both these techniques make use of the fast scanning of the RFeye receiver to form wideband bearing estimates for every frequency bin in the FFT. With wider band signals the frequency selective fading can be represented on a polar chart.
Is there a way to combine AoA and TDOA?2020-06-15T13:16:13+00:00
Yes, the system can use several geolocation techniques, including AoA, PoA and TDOA, simultaneously. The software is smart enough to be able to use any combination of these if appropriate and enabled. The results can be overlaid on a moving map display.
What if the transmitter changes its position continuously?2020-06-15T12:50:37+00:00

The system is capable of tracking moving targets, or moving node sensors. CRFS regularly tracks moving targets, and has also tracked targets using a mobile DF array (e.g. rabbit-hunting missions).

How can DF performance be improved in a noisy environment?2020-06-15T12:36:23+00:00

There are a number of techniques that can be used to eliminate or isolate interference and noise, including squelch (above and/or below the signal), frequency exclusion zones (essentially a frequency mask to block certain areas), intelligent averaging and several proprietary algorithms used to improve accuracy.

Watch the AoA Webinar [17]

Want to find out more about Angle of Arrival/Direction Finding?

Watch the AoA Webinar [17]