This is the last of a five-part series from Keysight Technologies on using real-time spectrum analysis to overcome RF/microwave interference in the field. You can download the entire series in a single app note here.

Part 5: Carrying precision into the field

Every piece of gear in a field kit has to prove its worth — and that’s the driving idea behind Keysight’s FieldFox family of handheld analyzers. In applications such as interference troubleshooting, FieldFox analyzers help engineers and technicians quickly detect issues, locate the source of the problem — whether it is an interfering signal or faulty component — and, after implementing a fix, verify system performance.

The analyzers deliver precise microwave and millimeter wave measurements and possess key attributes that support routine maintenance, in-depth troubleshooting and virtually anything in between:

• Frequency coverage: 5 kHz to a maximum of 50 GHz
• Multiple capabilities, including cable and antenna tester (CAT), spectrum analyzer, real-time spectrum analyzer (RTSA), power meter, vector network analyzer (VNA), power meter, independent signal source, frequency counter and GPS receiver
• Rugged design meeting MIL PRF 28800 F class 2, type tested for IP 53 and MIL-STD 810G 511.5 process 1 (explosive environment)
• Field ready, weighing 7.1 lb (3.2 kg) with a typical battery life of approximately 4 hours.

A built-in interference analyzer provides the ability to record and play back captured signals. FieldFox can also perform pulse measurements using its spectrum analyzer mode and a USB peak power sensor.

The FieldFox RTSA specifications are exceptional in field testing. The analyzers fare quite well when assessed versus the key indicators of RTSA performance. For most over-the-air (OTA) applications, the maximum real-time bandwidth (RTBW) of 10 MHz is more than sufficient, because external interference typically occurs within a much narrower band. Another crucial spec is probability of intercept (POI), which is the minimum duration of a signal of interest that can be detected with 100 percent probability and measured with the same amplitude accuracy as when observing a CW signal. A FieldFox with RTSA has POI performance of 12.2 µs (best case with 10 MHz span and max RBW) and can detect signals as narrow as 22 ns.

The driving force behind modern communications systems is providing the highest capacity at a given bandwidth. To meet this goal, networks are time division multiple access (TDMA) in nature, so many users can share the same channel. In addition to the bursty nature of signal characteristics, tight frequency reuse is widely deployed to increase overall network capacity. This introduces co-channel interferences inside networks. Gap-free spectrum analysis or RTSA is necessary to enable field engineers and technicians to troubleshoot interference issues.

Radio systems are getting more and more complex, and they are required to support multiple radio formats. For example, public safety radios need to support 6.25, 12.5 and 25 kHz channels for both analog and digital modulation. System field engineers need to verify both the spectrum performance of the network, as well as the timing profiles of control and traffic channels. RTSA density display with persistence provides unique insights on signal operation, which are not possible with traditional spectrum analyzers.

Interference is a symptom, and there are deeper root causes. Hardware failures like problems with the antenna, cables, diplexer/duplexer and low noise amplifier can and will induce interference in the network. A FieldFox handheld analyzer, which combines the functions of a spectrum analyzer, RTSA, cable antenna tester, vector network analyzer and independent signal source, used with a directional antenna, is a valuable tool for detecting, locating and fixing interference issues in the field.

End of Part 5. Read Part 4.

FieldFox RTSA software, Option 350, is designed for engineers and technicians performing interference hunting and signal monitoring, specifically in surveillance and secure communications, radar, electronic warfare and commercial wireless markets.