Interference Direction Analysis. Communication Signals

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3 1 PLC Power Line Communications I/Q Analyzer-Magnitude: The display here captures the entire signal in the time domain over a bandwidth of almost 27 MHz, making precise triggering easier. I/Q Analyzer-HiRes Spectrogram: The gapless display shows the PLC signal with a bandwidth of MHz over ms with a time resolution of 2.4 µs. I/Q Analyzer-HiRes Zoom: This uncompressed display can be scrolled over the entire range of measurement values. Initially, the service was limited to the short wave frequency band. The excluded frequency blocks protected wireless services in the corresponding bands. The frequency range has since expanded well into the VHF range and also makes use of intelligent frequency management. The analysis uses I/Q mode, which acquires and saves 250,000 I/Q pairs as a block. This allows gapless display of time versus frequency. Within this block, a POI (probability of intercept) of 100 % is offered, which can indicate results down into the nanosecond range depending on the settings.

4 2 ATC Air Traffic Control Spectrum: Simultaneous display of a 20 MHz span that is refreshed every 39 ms ensures correct classification of interference. Spectrogram: A time resolution of 500 ms was selected in order to show wireless traffic and interference carriers over a long period. I/Q Analyzer-Persistence: Display of probability density function unveils even shortest signals. It offers 100% POI (probability of intercept) down to Nano second pulses. Two opposing requirements apply to air fields. Radar may be present at a field strength much higher than 140 dbμv/m whereas an interference carrier within the air traffic control band can be well below 0 dbμv/m. The IDA is optimized to deal with these problems thanks to the 50 db range attenuator switchable in 1 db steps and the preamplifier with its high intermodulation immunity. IDA can handle field strengths of up to 100 V/m and in most cases can measure a radar signal as well as reliably detect the minimal interference carriers on the security frequency without an external attenuator.

5 3 TETRA Terrestrial Trunked Radio I/Q Analyzer-Persistence: The overview in I/Q Mode shows the continuous carrier of the fixed stations. Spectrum: Spectrum of an individual station showing the typical hump right of center. Time Domain (Scope): Signal course reveals typical TETRA single timeslot (14,167 ms) and double timeslot. The base station transmits a training sequence every ms, which is visible in time domain. In contrast to most other digital transmission methods, a TETRA signal is based on a single I/Q modulated carrier (typically 6/4 DQPSK).

6 4 PMR Public Mobile Radio (with interference) Spectrum: Display shows a modulated and an unmodulated signal as well as a small carrier of unknown origin. I/Q Analyzer-Persistence: Display shows a transmission at MHz with neighboring transmissions (blue cloud) that may interfere with adjacent channels. I/Q Analyzer-HiRes Spectrogram Zoom: The image shows more details of the transient response and how adjacent channels are affected by this. The example shows images of a case of interference caused by the transient response of a device. If the spectrum does not give any answers, other displays such as "Time Domain Scope" or "I/Q Analyzer" may help to track down the cause.

7 5 Pager Spectrum: The Max Hold trace shows all three hopping frequencies of a pager. Spectrogram: The display summarizes 500 ms in one line of the spectrogram (time resolution). By that it is possible to recognize the switching interval of 28 s between three frequencies. I/Q Analyzer-HiRes Spectrogram Zoom: The modulation becomes transparent. Transmitter overlaps would be visible, even with small time offsets on the same frequency. The service is FSK modulated (frequency shift keying), based on the POCSAG protocol. It switches every 28 seconds between three RF channels and can also be blanked. In the example, up to three stations at different distances are using each frequency in turn. The high frequency resolution shows that time overlaps (confusion areas) should not be suspected, as these would otherwise be easily seen. Use a wide span to get an initial overview and then reduce it for more exact analysis. Use HiRes Spectrogram (optimized time and frequency resolution at once) in order to indicate FSK modulation scheme.

8 6 GSM Global System for Mobile Communications (2G) I/Q Analyzer-HiRes Spectrogram: Downlink Extraneous signals are easily traced because they differ in frequency, bandwidth, and burst duration. Time Domain (Scope): The display shows the accumulated signal course of 25 channels simultaneously by applying a CBW of 5 MHz around the center frequency of 955 MHz. Time Domain (Scope): A different view shows one channel only. It reveals the GSM time slots (577 μs) and even different modulation schemes (GMSK for GSM, 8 PSK for EDGE). GSM stations are subject to the same standards worldwide. A frame is ms long and has 8 timeslots with a burst length of 577 μs. The frequency spacing is 200 khz. Since a GSM signal is broader than this, adjacent channels are not used at the same location/base station. High field strengths are present at a GSM base station. IDA works in environments of up to 100 V/m. A 20 db attenuator is recommended for above 10 V/m. Gapless monitoring for up to 24 h is possible with Time Domain (Scope). Apply the IDA I/Q Analyzer in order to even indicate BCCH signaling!

9 7 LTE Long Term Evolution (4G) Spectrum: In band interference is hardly visible within the spectrum because the data space is fully utilized. Single FFT windows are offered with up to 20 MHz spans ensuring uninterrupted capture of whole signal (even with interferers) without need of stitching mode. LTE uses widely differing frequencies and various procedures. I/Q Analyzer-HiRes Spectrogram: In band interference is more easily seen in this view, depending on the occupation density. I/Q Analyzer-HiRes Spectrogram Zoom: Regular structures can still be seen even in densely occupied areas with the zoomed view. In band interference can often be made easier to see by careful alignment of the antenna or by shielding the payload signal (e.g. behind a building or vehicle). 8

10 8 DECT Digital Enhanced Cordless Telecommunications Spectrum: Since the stations only transmit for 90 µs every 10 ms, detection using Spectrum is unlikely. The Night view mode shown here reduces eye strain. I/Q Analyzer-Persistence: The display shows the expected DECT bursts (blue cloud). The yellow colored intermodulation products come from neighboring GSM downlinks. I/Q Analyzer-HiRes Spectrogram: The gapless spectrogram delivers the evidence for GSM intermodulation. The 550 µs burst can be seen at some points. Operates in Germany between 1.88 and 1.9 GHz with a CBW of MHz. The transmission is broader than the spacing. Each frame lasts 10 ms and has 24 timeslots (12 each for uplink and downlink). Fixed parts idle mode shows a 90 μs burst every 10 ms (except EcoDECT). The burst length rises to 370 μsspaced precisely every 5 ms, but not necessarily on the same frequencies for a voice link between the fixed part and portable part. The question whether an IM3 product is home made can be answered easily using the 5 db keys. True IM3 does not alter with attenuation. The origin of IM3 can only be determined with difficulty in the field. The modulation locations (gutters, rusty bolts, own radio receiver) are inaccessible.

11 9 UMTS Universal Mobile Telecommunications System (3G) Spectrum: The spectrum shows even distribution due to the dense occupancy of the message space. This can change in case of multipath propagation. Spectrogram: Shows both UMTS up and downlink. HiRes Spectrogram: No further signal information even when applying a time resolution of just 4.8 µs! In Germany UMTS uplink lies between MHz and MHz whereas UMTS downlink lies between MHz and MHz. The bandwidth of one UMTS channel is 5 MHz. Based on WCDMA access UMTS applies PSK or QAM modulation.. In band interference can often be made easier to see by careful alignment of the antenna or by shielding the wanted signal (e.g. behind a building or vehicle).

12 10 Bluetooth Spectrum: Bluetooth Inquiry Mode The device is searching for other devices. This uses every second frequency and leaves a gap around 2.42 GHz. I/Q Analyzer-Persistence: Persistence shows a7.8mssectionof25mhz. I/Q Analyzer-HiRes Spectrogram: The display shows the typical pattern for Inquiry Mode. Bluetooth uses the frequency range between and MHz in the ISM band, in which 79 channels are defined. Frequency hopping principle repeats the channel sequence only after one day! The Burst length is 625 μs. Based on packet size, frequency is swapped after ms maximum. Interference on Bluetooth is usually rare because of the changing frequency, short range, and error correction.

13 11 WLAN Wireless Local Area Network Spectrum: Display shows active channel in Max trace with typical dips. Time Domain (Scope): Time Domain shows the time behavior. This is a valuable aid to correctly establishing the trigger level. I/Q Analyzer-HiRes Spectrogram Zoom: Shows the area of importance (trigger point) in a gapless spectrogram. At 2.4 GHz among other frequencies. Time and frequency multiplexing can barely be assessed using spectrum analysis only. Analyzing short term signals such as WLAN is easier when applying Max trace in spectrum. In some cases Act trace can be useful, too, in order to indicate modulation schemes.

14 Light, portable signal analyzer for detecting, analyzing and localizing RF signals and interference in the frequency range from 9 khz to 6 GHz. IDA 2 combines a frequency scanner / receiver, transmitter detector, spectrum analyzer, signal analyzer and triangulation software in a single mobile device. The sets also include precision directional antennas with built in switchable preamplifier and electronic compass.