1What a compliance survey reports

The deliverable is a document saying, with a signature on it, that a location is below a published exposure limit. A rooftop, a tower base, a schoolyard sixty meters from a macro cell. It is read by the site owner, the network operator and the regulator, and it is compared with the surveys that follow it.

Three things go wrong in such a survey, and only one is an instrument fault. Max hold on a burst without duty correction over-reads by 10 log(1/δ), where δ is the duty cycle: 30 dB on a radar at one part in a thousand. A cable loss read at the wrong frequency row loses 2.4 dB. And a survey can answer a different question from the one the limit asks.

That last case is the subject here, because it does not look like a failure. Instrument calibrated, operator careful, every number traceable, and the result low by a factor near 700 on the carrier worked in section 4.

2What is limited, and by which quantity

Standards work in two layers. Basic restrictions, the dosimetric reference limits of IEEE C95.1-2019 and ICNIRP 2020, are in-body quantities not measurable in the field: whole-body average SAR over 30 minutes, local SAR in a 10 g cube over 6 minutes, absorbed power density above 6 GHz. Reference levels are external field quantities derived conservatively from them, and they are what a survey measures.

A template written for the 1998 guidelines is therefore wrong twice over. The whole-body averaging window moved from 6 minutes to 30, and a local-exposure limit surface appeared where none existed. Neither error is visible in the final percentage.

Figure 1 plots the reference levels the rest of this paper is scored against, and the two regimes a survey has to choose between.

3From a receiver reading to a field strength

In the far field E and H are locked together by the impedance of free space, so power density follows from either alone:

Equation (1) does not apply in the reactive near field, where a power-density readout reports a quantity that does not exist. One check to carry: √3770 is 61.4 V/m, exactly the FCC occupational limit from 30 to 300 MHz, which is 10 W/m² expressed as a field. Figure 2 shows where each term of the chain enters.

Written out, the chain is:

Antenna factor is the ratio of incident field strength to the voltage across a 50 Ω load, a property of the terminated antenna. With the aperture relation, equation (1) gives the identity every calibration certificate implies:

Check it: a half-wave dipole at 100 MHz gives 40.00 − 2.15 − 29.77, or 8.08 dB(1/m), against a published figure near 8.1. Back the implied gain out of any certificate and ask whether it is plausible for that aperture. A certificate implying 15 dBi from a biconical is a typing error, caught before the survey. Figure 3 shows the correction applied inside the instrument.

4Time, traffic, and the maximum

Everything adds in power, never in field, and every source in every band is a term:

Ratios are squared before summing, so three sources each at 60 percent of their own reference level total 1.08 and the site fails with no reading above 60 percent. Every unmeasured band is a term set to zero.

Limits are on the maximum time-averaged exposure, 1800 s whole body and 360 s local. A traffic-dependent transmitter radiates what demand asks of it, and roof access is granted when it is granted. IEC 62232 and ITU-R SM.2452-1 resolve that by scaling an always-on component:

The worked example, in full

A 3.5 GHz macro cell: 100 MHz channel, 30 kHz spacing, 3276 subcarriers, an eight-beam burst set every 20 ms, a DDDSU frame, a declared 6 dB traffic-to-broadcast ratio. All values are illustrative and chosen so the arithmetic can be checked.

The receiver reads −33.2 dBm on the strongest secondary synchronization resource element, with antenna factor 35.10 dB(1/m) and 2.0 dB of cable loss. Equation (2): −33.2 + 106.99 = 73.79 dBµV, then 73.79 + 35.10 + 2.0 = 110.89 dBµV/m, or 0.3503 V/m. Equation (3) puts the implied gain at 6.01 dBi, so the certificate stands, and equation (1) gives 0.3503² / 376.73 = 3.258 × 10⁻⁴ W/m².

Then the factors. 98.28 MHz over 30 kHz is 3276. Downlink duty is (3 × 14 + 10)/70 = 0.743, taken as 0.75. No limiter is declared, and 6 dB is a factor of 4. The product is 9828, so equation (5) gives 3.202 W/m²: 32.0 percent of the 10 W/m² general-public limit above 2 GHz.

The raw reading would have said 0.0033 percent. A shaped broadband probe integrates the whole burst instead: all 240 subcarriers are on during a synchronization symbol, giving a 5.43 V/m burst, and at 5.71 percent duty the 30-minute average is 0.045 percent. Section 5 takes up what that number can and cannot support, and Figure 4 shows why the two readings differ.

Table 1 decomposes the gap term by term, and every term in it is a property of the network rather than of the instrument.

Put that carrier on a rooftop with three others and score the site against the ICNIRP 2020 general-public reference levels: FM at 15.0 V/m against 27.7 V/m, GSM 900 at 12.0 V/m against 42.32 V/m (1.375 × 947^0.5), LTE 1800 at 20.0 V/m against 59.01 V/m (1.375 × 1842^0.5). The squared ratios with the 5G term raw sum to 0.489. Extrapolating that term takes the sum to 0.809, and Figure 5 shows where the budget then lies.

5Where the broadband survey falls short

The method compared here is the shaped isotropic broadband probe read as one percent-of-limit number. Shaped to the reciprocal of the reference-level curve, it implements the exposure sum in hardware, and if the question is whether a rooftop has a hot spot, and where, it answers it faster than anything else. It falls short of the extrapolated maximum for four structural reasons, none of them a matter of probe quality.

• It returns a scalar where the method requires terms. A probe gives the sum in equation (4) and discards the terms, so no extrapolation factor can be applied.
• It cannot extrapolate, because it measures a different quantity. A probe reading already contains −23.80 dB of occupancy and +12.43 dB of duty, so multiplying it by 3276 double-counts both. Structure cannot be recovered from a scalar.
• The detector is non-conservative on the modern signal. SM.2452-1 notes that diode probes driven above their true-RMS range err on high-crest signals, and compression produces a low reading.
• The shaping curve encodes a standard, and the standard moved. A probe shaped to ICNIRP 1998 reports against a 6-minute whole-body assumption, and the reader of the number cannot tell which limit surface it was shaped to.

The limit holds for an ideal probe. Grant it a perfect true-RMS detector, an exact shaping curve, isotropy to a hundredth of a decibel and unlimited sensitivity. It still returns the sum rather than the terms, and equation (5) needs the terms. The limit is the quantity measured, not the precision of the measurement.

The complementary limit applies to the frequency-selective survey: without a preceding broadband scan, nine tripod points are nine samples of a field with maxima every 43 mm at 3.5 GHz. The method is both instruments, in that order.

6Derived requirements

Table 2 converts the physics into requirements a reader can score any receiver against, including ones we do not make.

Table 3 shows where the 3.0 dB in R4 comes from, and its last row is not an instrument term. Figure 6 draws the same budget as variances.

7Meeting the requirements

An exposure measurement system at scale is assembled rather than bought whole. An integrator pairs a receive module with a calibrated antenna set and software of their own, so the receiver has to hold its amplitude accuracy across the band, cover that band in one calibrated chain, take commands from someone else's software, and fit a mast or a case. A safety officer carries a handheld. The ICX-FieldHawk family covers both on one measurement set in three form factors: the handheld (4.5, 6 and 9 GHz models, and 9.5, 20 and 40 GHz models), the ICX-FieldHawk-R IP68 tablet (9.5, 20 and 40 GHz), and the ICX-200U and ICX-400U modules over USB or LAN, the USB module under 420 g. Each requirement below carries its published value and condition, and the summary table of section 9 collects them.

R3. Published single-sideband phase noise at a 1 GHz carrier and 10 kHz offset is −107.5 dBc/Hz for the 40 GHz models (ICX-400, ICX-400R, ICX-400U), −101.6 dBc/Hz for the ICX-095 and ICX-095R, and −99.7 dBc/Hz for the 20 GHz models, all at 25 °C after 10 minutes of warm-up with spur reject standard on; the ICX-090 handheld publishes −110 dBc/Hz guaranteed and −112 typical. An adjacent carrier at −10 dBm throws a skirt of −10 − 107.5 + 10 log(30,000) = −72.7 dBm into 30 kHz, so a resource element at −60 dBm is 12.7 dB clear and takes 0.23 dB of error. On the 9.5 GHz models the margin is 6.8 dB and the error 0.82 dB; on the 20 GHz models 4.9 dB and 1.21 dB; on the ICX-090 handheld 15.2 dB and 0.13 dB. R3 as written is therefore met by the 40 GHz models and the ICX-090, and the 9.5 and 20 GHz models fall 3.4 and 5.3 dB short of it.

R4. Published amplitude accuracy on the 9.5, 20 and 40 GHz models is ±2.0 dB from 9 kHz to 9.5 GHz and ±3.0 dB from 9.5 to 40 GHz, at 25 °C after 10 minutes of warm-up with spur reject standard on. Substitute ±2.0 dB into the budget for the ±1.5 dB illustrative term and the sum becomes 2.778, so U is 3.3 dB, above the 3.0 dB target of R4, and above 9.5 GHz it reaches 4.2 dB. The ICX-045, ICX-060 and ICX-090 handhelds publish ±1.0 dB from 20 to 30 °C under typical conditions and ±1.5 dB over the full temperature range and all conditions, which is the budget's own term and meets R4 as published to 9 GHz. On the other models, meeting R4 needs a site amplitude correction against a calibrated reference, which is why the published amplitude correction and Amplitude Offset functions belong in the method; Figure 7 shows the offset applied. Any receiver quoting one ex-factory figure has the same arithmetic; what differs is whether the correction path exists.

R2. The RMS detector is published on every model, and power detection records power against time at 8 ns resolution on the 9.5, 20 and 40 GHz models (16 ns on the 4.5, 6 and 9 GHz handhelds, 8 ns with option 50). The averaging window of R2 is not a published parameter; it is applied to that record by the survey software, which is where an integrator's product carries it. A declared duty assumed higher than the frame runs over-states the maximum, which is safe; a frame declared at 0.55 but running at 0.743 costs 1.3 dB in the non-conservative direction, and the power-against-time record is how the duty is measured rather than declared.

R5. The published antennas are an omnidirectional element (option 34, 400 MHz to 8 GHz) and an active directional antenna (option 35), neither a three-axis isotropic probe, so total field comes from three sequential orientations added in quadrature, exact only for a stationary field. Channel Power and Antenna Factor are among the published measurement functions a survey uses at every point, included rather than licensed.

R7. Antenna factor correction belongs inside the chain, not in a spreadsheet afterward, as Figure 3 showed: the correction table is applied at the instrument, so the logged value is already a field strength. The host application, SpectraCore, drives that over SCPI with published bindings for C, C++, C#, Python, MATLAB, Qt and LabVIEW, and an integrator whose survey software is the product can bypass SpectraCore and drive the module directly.

8Measurement practice

Figure 8 is the measurement the exposure chain consumes, and the practice list below exists to make that one number reproducible.

Most of what makes a survey reproducible is method rather than receiver.

1. Scan before you measure. Broadband probe for where the maximum is, frequency-selective for what it is made of.
2. Spatially average in power, not in field: the root mean square of the fields, never the mean of the V/m readings, and no closer than 0.5 m to a conductive object.
3. Record the integration time per measurement, not once per day: under 577 µs for a GSM timeslot, under 0.5 ms for a Wi-Fi beacon, 72 s or less from 2 to 6 GHz. Log every extrapolation factor with its source, and state U, k, and which uncertainty convention was applied.
4. Cross-check every point by effective aperture: the same power density from P_rec divided by Gλ²/4π has to agree within 0.5 dB. In the worked example the two routes agree to 0.01 dB.
5. Name the regime. State whether the sum was scored against ICNIRP 2020 or 47 CFR 1.1310, general public or occupational, because the reference levels differ by up to 7 dB and a percentage without its regime cannot be compared with a later survey.

One limit of the state of the art belongs in every report. Where the point lies outside the synchronization beam sweep, SM.2452-1 requires the measurement to be made in a traffic beam and states that methods for attracting one are still under development. A survey assuming the easy case is non-conservative by up to 9 dB, and no instrument closes that gap. Theoretical-maximum extrapolation also runs 5 to 9 dB above the actual-maximum assessment IEC 62232:2022 permits, so the report says which convention was used.

Field evidence

The instrument a safety officer carries is increasingly an integrator's product with a general-purpose receiver inside it, built with the integrator's own antennas and software. That arrangement puts the arithmetic of sections 4 and 5 on the integrator rather than on the officer, and it is why this paper spends its length there. The failure reported from the field is not a sensitivity failure. It is a survey that was correct, traceable and signed, and answered a different question by 28.6 dB.

9Summary, definitions and further reading

Table 4 collects the governing relations and published values with their conditions.

Basic restriction

An in-body exposure quantity tied to the biophysical effect, not measurable in the field. Extrapolation is its complement: scaling an always-on signal to the maximum traffic load.

Reference level

An external field quantity derived conservatively from a basic restriction. Compliance with it guarantees compliance; exceeding it is not a finding. The total exposure ratio sums each source's contribution over its own reference level, field ratios squared, and must not exceed 1.

Further reading

• ICNIRP, Guidelines for Limiting Exposure to Electromagnetic Fields (100 kHz to 300 GHz), Health Physics 118(5), 2020.
• IEEE Std C95.1-2019, Safety Levels with Respect to Human Exposure to Electric, Magnetic and Electromagnetic Fields.
• Report ITU-R SM.2452-1, Electromagnetic field measurements to assess human exposure; IEC 62232:2022; 47 CFR §1.1310; FCC OET Bulletin 65 Edition 97-01; ISO/IEC Guide 98-3:2008.

If you are building an exposure product around a receive module, or specifying what a survey report has to contain, our application engineers would be glad to work through the chain and the budget with you.