The level shown on a signal generator is not necessarily the level at a cellular receiver input. External path loss and calibration define the relationship.
Why this matters in the industry
Receiver sensitivity work depends on a small delivered signal. Cables, pads and fixtures can introduce several decibels of loss that must be distinguished from the generator setting.
The technical reasoning
A source display usually describes its own configured output plane and operating mode. The cellular receiver sees the signal after every intervening cable, switch, coupling element and level-control stage. The route model also needs the source's waveform calibration convention; a continuous-tone calibration may not identify the delivered modulated average under different settings.
Understanding level, loss and the measurement plane
RF power in dBm is an absolute level referenced to one milliwatt; dB describes a ratio. A source level can be propagated through a linear, matched path by subtracting losses and adding gains. That arithmetic becomes a measurement model only when each term applies to the actual frequency, signal state and reference plane. A nominal component value is not the same as a characterized complete route. Mismatch, connector variation and frequency response can make the delivered level differ from the simple estimate.
How to structure the investigation
Measure loss to the device reference plane using an appropriate calibration method. Subtract that loss from the source level and include measurement uncertainty. Recheck the path whenever an attenuator state, adapter or cable changes, and record the actual setup used for each result.
Build a route model before interpreting the device result. Separate source uncertainty, measured transmission loss and the final observed quantity. Check that the receiver or analyzer remains within a useful linear range, and verify at least one independent reference condition. When a route changes, review the correction rather than carrying it forward automatically. Record raw and corrected levels so a later reviewer can reconstruct the calculation and identify a sign or units error.
Worked example or engineering scenario
For an assumed minus-40-dBm source and 30.7 dB measured route loss, the estimated receiver stimulus is minus 70.7 dBm. Report route uncertainty with that estimate rather than rounding it into an exact sensitivity value.
Evidence to collect
| Record | Purpose |
|---|---|
| Define the DUT plane | Defines the tested state and scope of the comparison. |
| Measure external loss | Makes the stimulus or route condition reproducible. |
| Track attenuator states | Supports interpretation of variation and possible confounding effects. |
| Record corrected input level | Connects the observation with the stated engineering decision. |
Trade-offs and common interpretation errors
A correct calculation can still describe the wrong interface. State where the result applies, whether power is averaged over time or a selected burst, and which route terms are measured rather than assumed. Changing attenuation can also expose noise or overload effects, so an output change is not always a simple loss change.
What the result can support
Define the receiver input plane and retain the source configuration with each reported stimulus.
The calculation assumes the measured loss remains applicable to the connected setup and operating conditions.
Further technical reading
Related industry knowledge
- Passive Intermodulation and Ordinary RF Accessories
- 5G Handover Testing: What an Attenuator Can and Cannot Do
Numerical scenarios are illustrative assumptions, not reported measurements of a supplied product or installation.