Two devices. Same model. Same show. Same table.
Both were Keysight FieldFox Microwave Analyzers — the N9953B, rated to 54 GHz.
But they were showing completely different things.
The left one: a pulse sequence generator running at 14,000.00 MHz, amplitude set to −5.00 dBm, displaying the structured timing of a pulsed waveform. Clean pulse edges. Defined on/off intervals. The kind of signal used in radar systems where timing is everything.
The right one: a live spectrum capture, center frequency 94.000000 GHz, resolution bandwidth 10 Hz, video bandwidth 10 Hz — with a VDI PSAX frequency extender (Model No: PSAX, S/N: PSAX 001) mounted on top of the instrument. A gold horn antenna pointing up. The screen showing a signal peak rising above the noise floor, surrounded by the characteristic roughness of a real-world mmWave measurement environment.
One device was generating and characterizing a time-domain pulsed signal. The other was detecting and analyzing a 94 GHz spectral environment.
Same chassis. Completely different measurement world.
What the VDI WR12 extender actually does
The VDI WR12 module on the bench — labeled clearly: WR 12, 60–90 GHz — is a frequency extender made by Virginia Diodes Inc. The second unit mounted on the N9953B showed Model: PSAX, operating around 94 GHz.
This is not a trivial accessory.
The FieldFox N9953B is rated to 54 GHz natively. To measure signals in the 60–90 GHz W-band or beyond, you need a frequency extender that: → Takes the analyzer's output at a lower intermediate frequency → Multiplies it up to the target mmWave band → Down-converts the received signal back for the analyzer to process
The WR12 waveguide aperture is approximately 3.1 mm × 1.55 mm — small enough that you're handling something that feels almost like a precision optical component rather than a microwave connector. The gold horn antenna visible in the photos is a standard gain horn for W-band, providing a known antenna factor for the calibration chain.
This combination — a rugged handheld analyzer plus a waveguide frequency extender — turns a field instrument into a mmWave measurement system that you can carry in a backpack.
That is not something that was possible at reasonable cost a decade ago.
The interference hunting scenario
The wall behind the booth said it directly:
"Precision RF Field Test" → Deploy the lightest μW analyzer → Analyze in real time → Scan 5G OTA and beyond
And the screen to the left of the devices showed something more concrete: a Dynamic Spectrum Sharing test (5G NR / LTE FDD / TDD) capture, with GPS coordinates visible (38° 14' 16.973" N, 122° 35' 15.546" W — somewhere in California), elevation 36.40 meters, antenna locked.
The scan results table below showed cell-by-cell measurements: RSRP, RSRQ, RSSI, SNR — across multiple carriers, with values ranging from −74.25 dBm down to −107.31 dBm.
This is a real deployment scenario.
An engineer with a FieldFox in the field, walking a site, capturing the actual over-the-air signal environment of a 5G NR / LTE coexistence deployment. Not a lab simulation — a GPS-tagged, time-stamped measurement of what's actually transmitting, at what power, from which cell.
The second screen next to it displayed a FieldFox running direction-finding mode — a polar plot showing bearing and signal strength, with "Antenna Connect" and "Bearing Colors" visible on the softkey menu. That's interference localization: you rotate the antenna, the bearing plot updates, you triangulate the source.
→ This is what "field test" means in practice. → Not bench verification. Physical space. Real interference. Unknown environment.
Image 3: the directional antenna on the bench
The flat panel visible in Image 4 in front of the two devices is a directional antenna — a log-periodic or Yagi-style flat panel used for bearing measurement and signal source localization.
It's easy to overlook in a trade show context. But it represents the complete field measurement chain:
→ Horn antenna or omni for initial spectrum survey → Directional antenna for bearing determination → FieldFox for logging, GPS tagging, and display
The fact that Keysight brought this antenna to the booth, alongside the mmWave extender and the 5G NR DSS demo, is telling. The target user for this setup is not sitting at a lab bench. They are on a rooftop, in a parking lot, at a cell site, or inside a building trying to find out where an interference source is — and they need equipment that can travel with them.
The frequency range problem this setup solves
The question that these demos collectively addressed: how do you test RF systems that operate at frequencies your instrument wasn't designed for?
The FieldFox N9953B goes to 54 GHz.
But 5G mmWave is at 26 GHz, 28 GHz, 39 GHz — well within range. Automotive radar is at 77 GHz — requires an extender. Satellite communication and imaging systems operate at 94 GHz and above. 6G research is already pushing past 100 GHz, into the terahertz gap.
Each frequency band adds measurement challenges that compound: → Connector repeatability becomes critical — a loose WR12 waveguide connection changes insertion loss by several dB → Atmospheric absorption at 60 GHz is significant — oxygen absorption creates a natural propagation limit that changes how you interpret signal levels → Antenna gain factors must be applied precisely — a 1 dB error in the antenna correction changes every measurement
The VDI extender + FieldFox combination addresses the instrument side of this problem. It does not remove the physical complexity of measuring at these frequencies. But it makes the instrument chain portable, calibrated, and rugged enough to bring out of the lab.
Why this matters for applications beyond telecom
The FieldFox is marketed as a field instrument for wireless infrastructure. But the frequency range this setup covers is directly relevant to several other engineering domains:
Automotive radar — 77 GHz and 79 GHz systems in every modern ADAS platform. Interference between vehicles in dense urban environments is an increasingly real problem that requires field measurement to characterize.
Industrial sensing — Level radars, material detection, process control systems operating in the 24–77 GHz range.
Satellite and defense — W-band systems, airborne radar, electronic intelligence gathering. The FieldFox's MIL-STD-810 ruggedness rating is not coincidental.
Data center wireless backhaul — Proprietary mmWave links operating at 60 GHz and above, increasingly used for rack-to-rack wireless interconnects in hyperscale facilities.
In each of these cases, the measurement problem is the same: you have a signal at a frequency that your standard instrument doesn't reach, in an environment where you can't bring a rack of lab equipment, and you need a result that's accurate enough to make a real engineering decision.
The pulse mode demo: a different problem
The left FieldFox running at 14 GHz in pulse sequence mode was addressing a different measurement challenge entirely.
Pulsed RF systems — radar, EW, satellite uplinks — don't transmit continuously. They burst. The measurement problem is characterizing not just the frequency and power, but the timing: pulse width, rise time, repetition interval, duty cycle, and how the frequency behaves during the pulse.
The FieldFox in pulse mode can capture and display these characteristics directly. The amplitude shown on screen was −5.00 dBm — a controlled demo signal, but representative of the kind of CW or pulsed source that a field engineer might be calibrating against a reference or verifying against a specification.
→ Pulse testing and spectrum analysis are not interchangeable. → A spectrum analyzer captures the frequency content of a pulsed signal but tells you nothing about the timing structure. → Pulse mode shows you the time-domain behavior but requires knowing roughly what frequency to tune to.
Both views are necessary for a complete characterization of a pulsed RF system. The FieldFox supports both in the same handheld chassis.
What the show was really demonstrating
Standing at this booth, the message from Keysight was not primarily about specification numbers.
It was about coverage.
Coverage of frequency — from DC-capable measurements to 94 GHz and above with extenders. Coverage of application — from radar pulse timing to 5G NR cell scanning to interference localization. Coverage of environment — MIL-spec ruggedized, battery-powered, GPS-integrated, small enough to carry.
The "lightest μW analyzer" headline on the booth wall is accurate — the FieldFox weighs under 3 kg fully loaded.
But the more important claim is the one embedded in the demo setup:
A single instrument family, with the right accessories, covers a measurement domain that would have required three separate instruments a generation ago.
That compression of capability into a portable form factor is what defines the current state of RF field measurement — and what engineers working on mmWave systems in any application domain are going to need more of as signal frequencies continue to rise.
All photos: Thomas · @SignalByThomas