A Microwave Oven as the Device Under Test
At the Gauss Instruments booth at the EMC exhibition in Cologne this January, the DUT had changed.
In the previous demo — the TDEMI ULTRA — it was a table lamp. A small LED driver with a switch-mode power supply, generating switching harmonics from 50 kHz through the hundreds of MHz.
Here, next to the TDEMI G Series instrument, sat a Toshiba microwave oven.
The choice is deliberate, and the contrast with the lamp is instructive. A microwave oven is not just a more complex EMI source. It is a fundamentally different class of EMI problem — one that illustrates precisely why 225 MHz of real-time bandwidth, combined with 1 Hz to 44 GHz total coverage, describes something specific about what this instrument family is designed to handle.
Gauss Instruments TDEMI G Series · 225 MHz real-time bandwidth · 1 Hz – 44 GHz · Toshiba microwave oven as DUT · "Full Compliance Measurements for All EMC Testing and Requirements" · EMC exhibition, Cologne, Germany, January 2026 Alt text: Gauss Instruments TDEMI G Series 225 MHz real time bandwidth EMI analyzer with Toshiba microwave oven as device under test at EMC exhibition Cologne Germany 2026 Photo: Thomas · @SignalByThomas (X)
Why a Microwave Oven Is a Serious EMI Test Subject
A household microwave oven contains a magnetron — a vacuum tube oscillator that generates the 2.45 GHz microwave energy used for cooking. The magnetron does not generate a clean, stable carrier. It produces a broadband noise-like emission centered on 2.45 GHz with sidebands that can extend hundreds of MHz in both directions, plus harmonics at 4.9 GHz, 7.35 GHz, and beyond.
Additionally, the microwave oven's power control circuit — typically a TRIAC-based phase controller that chops the AC mains waveform to reduce average magnetron power — generates conducted and radiated emissions at mains harmonics (50 Hz, 100 Hz, 150 Hz...) and at the TRIAC switching edges, which contain energy up into the MHz range.
The result is a device that simultaneously produces:
→ Low-frequency conducted emissions from the power control circuit (150 kHz – 30 MHz CISPR range)
→ Broadband microwave emissions centered at 2.45 GHz with wide spectral spread
→ Harmonic emissions of the magnetron fundamental into the 5–10 GHz range
→ Intermittent behavior — emissions change with magnetron duty cycle, power level setting, and load conditions
A microwave oven is therefore not a simple EMI test case. It is a multi-decade, multi-mechanism emission problem that must be characterized across the full CISPR frequency range simultaneously if the measurement is to be meaningful. The 225 MHz real-time bandwidth of the TDEMI G, positioned within a 1 Hz–44 GHz total range, is built for exactly this kind of measurement challenge.
The TDEMI G: The Entry Point to the TDEMI Architecture
The TDEMI G Series is the fourth instrument in the Gauss Instruments TDEMI family shown at this exhibition — and the most accessible entry point into the real-time EMI measurement architecture.
Across the booth, the bandwidth progression tells the product story:
→ TDEMI G Series (this demo): 225 MHz real-time bandwidth · 1 Hz – 44 GHz
→ TDEMI S Series (Article 020): 510 MHz real-time bandwidth
→ TDEMI Ultimate (Article 021): 1000 MHz real-time bandwidth
→ TDEMI ULTRA Series (Article 022): DC – 40 GHz real-time scanning
The G Series shares the core TDEMI® architecture — real-time IQ capture, density display, multi-detector analysis, replay capability — at a real-time bandwidth that covers the primary radiated emissions compliance range (30 MHz – 1 GHz) and the 2.4 GHz ISM band within a single capture window positioned at the right center frequency.
The white chassis distinguishes the TDEMI G visually from the darker S and Ultimate units. The front panel layout is recognizable across the family: GEN output for stimulus injection, RF 1 and RF 2 measurement inputs for two-channel or differential measurement configurations. The software interface — visible on the instrument's built-in display — carries the same tab structure across all models: Spectrogram / Receiver / SP Analyzer / RT Analyzer.
The product card's claim — Full Compliance Measurements for All EMC Testing and Requirements — positions the TDEMI G not as a pre-compliance or development tool, but as a complete compliance platform at its tier. The 44 GHz frequency coverage, extendable to THz via external mixer, preserves the architectural continuity of the family even at the entry level.
Reading the Display: Two Layers of the Same Measurement
The TDEMI G's screen shows the same dual-layer display architecture consistent across the entire TDEMI family.
Upper layer: EMI spectrum with colored peak markers
Multiple emission peaks are visible across the frequency span, each highlighted with a color-coded marker. The trace shows the emission profile of the microwave oven's operating state at the moment of capture — a mix of switching noise from the power control circuit at lower frequencies and the magnetron's broadband emission structure at higher frequencies. Limit lines would be overlaid in a compliance measurement configuration to show margin against the applicable standard.
Lower layer: density/spectrogram display
The green-to-yellow-to-red spectrogram shows the statistical distribution of emission events across frequency over the measurement duration. For a microwave oven, this display tells the compliance engineer something a single peak-hold sweep cannot: which emissions are present consistently across all magnetron duty cycles, and which appear only in specific power control states. An emission that appears red (constant) requires a different engineering response than one that appears green (occasional) — even if their peak amplitudes are identical on the upper trace.
This behavioral dimension of the measurement — not just what the device emits, but how reliably and under what operating conditions — is the direct product of real-time IQ capture. The density display is not a post-processing visualization. It is generated continuously from the live acquisition stream, updating in real time as the microwave oven cycles through its power control states.
The DUT Choice as a Teaching Tool
Across the four Gauss Instruments demos at this Cologne exhibition, the DUT choices form a deliberate sequence:
→ TDEMI S (510 MHz): Mini-ITX industrial board + LISN — conducted EMI from embedded electronics, standardized test chain
→ TDEMI Ultimate (1000 MHz): No specific DUT — 3D spectrogram demo via biconical antenna, radiated emissions characterization focus
→ TDEMI ULTRA (DC–40 GHz): Table lamp + small appliance — consumer electronics LED driver, broad-spectrum conducted + radiated
→ TDEMI G (225 MHz): Toshiba microwave oven — multi-decade, multi-mechanism, magnetron + power control emissions
Each DUT was chosen to illustrate a specific measurement challenge that the corresponding instrument's real-time bandwidth and frequency coverage addresses. The microwave oven is the most electromagnetically complex of the four — and it demonstrates the TDEMI G's compliance-oriented positioning most directly. A device that requires simultaneous characterization from conducted emissions at 150 kHz through magnetron harmonics at 7+ GHz is precisely the kind of DUT for which "full compliance measurements for all EMC testing and requirements" is the relevant specification.
225 MHz in Context: Why This Number, for This Application
The 225 MHz real-time bandwidth of the TDEMI G is not a compromised version of the 510 MHz S Series. It is a specific engineering specification for a specific measurement use case.
The CISPR 11 standard for industrial, scientific, and medical (ISM) equipment — which covers microwave ovens — defines limits in two frequency ranges: conducted emissions (150 kHz – 30 MHz) and radiated emissions (30 MHz – 1 GHz, with additional requirements at the ISM frequency 2.45 GHz). The radiated emissions measurement window from 30 MHz to 1 GHz spans approximately 970 MHz of frequency range.
A 225 MHz real-time capture window, positioned and stepped through the 30 MHz – 1 GHz range, covers the complete CISPR radiated range in a small number of capture positions — each position capturing 225 MHz of the range simultaneously, with no swept scanning within that window. For the 2.45 GHz magnetron emission, the same 225 MHz window centered at 2.45 GHz captures the magnetron fundamental and its immediate sidebands in a single capture.
The result is a real-time characterization capability that covers the primary compliance frequency ranges for appliance and ISM equipment without requiring either a swept receiver (which misses intermittent events) or a wider instantaneous bandwidth than the application requires. The G Series is not under-specified for its intended market. It is specified for it.
The Compliance-First Positioning of the TDEMI G
The product card language for the TDEMI G — Full Compliance Measurements for All EMC Testing and Requirements — is a more direct compliance claim than the other instruments in the family. The TDEMI S and TDEMI Ultimate are positioned more explicitly toward pre-compliance and development use cases. The TDEMI G claims compliance-grade measurement capability at the entry tier of the family.
This is the relevant positioning for the appliance and consumer electronics markets. A compliance test lab testing microwave ovens, LED luminaires, and power tools under EN 55014, CISPR 11, and CISPR 15 needs an instrument that produces results directly comparable to the certified EMI receivers those standards reference — not a development tool that approximates compliance but requires a formal receiver for final certification.
Whether the TDEMI G's real-time architecture fully satisfies the CISPR 16-1-1 receiver requirements across all detector modes and all frequency sub-ranges is the technical question a compliance lab would evaluate before adopting it as the primary measurement instrument. The Gauss Instruments claim is that it does. The deployment data from labs that have made that substitution is the ultimate evidence.
What the demo in Cologne showed is the measurement in action: a microwave oven being characterized in real time, with simultaneous spectrum and behavioral density visualization, on an instrument that fits in a compact desktop chassis and covers 1 Hz to 44 GHz. For a product category that has historically required a rack of separate instruments and a lengthy swept measurement sequence, that is a meaningful compression of the measurement workflow.
Instrument observed: Gauss Instruments TDEMI® G Series · 225 MHz Real-Time Bandwidth · 1 Hz – 44 GHz · TDEMI® Technology · "Full Compliance Measurements for All EMC Testing and Requirements" · with Toshiba microwave oven as DUT
All photos: Thomas · @SignalByThomas