Mobile Networks and Signal Testing
What this domain tests
Mobile Networks and Signal Testing tests cellular basics and practical signal faults: SIM, bands, antennas, RF path, signal metrics and data settings.
Core rules
- GSM, WCDMA, LTE and 5G NR use different bands and technologies. A phone must support the operator's band and be network-unlocked.
- The RF path runs from baseband/transceiver to PA, filter, antenna switch and antenna. A damaged antenna or connector causes weak or no service.
- RSSI, RSRP, RSRQ and SINR are RF metrics; bars are only a rough display. Data needs a correct APN; calls need network registration.
- Test with a known-good SIM and compare the same SIM in another phone. Check IMEI status and network lock.
- Airplane mode, disabled SIM, wrong network mode and local coverage can mimic hardware faults.
Worked example
A phone shows 'No service', but its SIM works in another phone. First check airplane mode, SIM detection and network selection. If the SIM is read but registration fails, inspect the antenna connector and tray. Compare signal strength in the same location with a known-good phone. If the known-good phone has strong RSRP and this one has none, the fault is in the phone's RF path, not the network. If both are weak, the issue may be coverage or band support. The reasoning separates SIM, settings, network and hardware.
Traps
Blaming the network before testing the SIM elsewhere; confusing Wi-Fi with cellular; assuming APN fixes calls; ignoring band support; testing signal inside a metal cabinet.