The chain, step by step
- The handset captures your voice the moment you press PTT, compresses it with a low-bitrate codec, and starts streaming it as data packets immediately — it does not wait for you to finish talking.
- The SIM and mobile network carry those packets over 4G LTE or 5G. PoC voice needs remarkably little bandwidth — a few kilobits per second — which is why it works in places where a video call would collapse.
- The PTT platform (the server layer) receives the stream, checks who's in the selected talk group, handles priority and floor control — who may speak when — and relays the audio out to every member.
- Every listening radio receives and plays the stream near-simultaneously. End-to-end latency on a healthy network is typically 300–600 ms — press, breathe, speak, and nobody notices.
Why multi-network SIMs are the real magic
The single biggest upgrade in real-world PoC performance is the roaming, multi-network SIM. A standard consumer SIM is locked to one operator; where that operator is weak, your radio is deaf. Multi-network SIMs — standard issue from serious PoC providers — can attach to any UK operator (EE, O2, Vodafone, Three) and switch to whichever signal is strongest where the radio is standing. In coverage terms, a PoC radio on a roaming SIM outperforms any phone in your pocket, because it always has four networks to choose from instead of one.
The platform layer: where the features live
The platform is what turns data connectivity into a radio system. Talk groups, private calls, priority and emergency calls, GPS tracking and history, lone-worker monitoring, text and photo messaging, and PC dispatcher consoles all live here. Established platforms in the UK market include Motorola's WAVE PTX, TASSTA, Zello and several white-label systems offered by radio dealers. Two practical notes: handsets are often locked to the platform they're sold with, and platform subscriptions — not hardware — are where providers differ most, so compare the software before the radio.
Indoors, underground and blackspots
Three honest scenarios:
- Weak signal: PoC degrades gracefully — the codec needs so little bandwidth that voice often keeps working at one bar where web browsing has given up.
- Indoor dead zones: most PoC radios fall back to Wi-Fi, so a warehouse with wireless coverage stays connected even inside a metal-clad building the mobile networks can't penetrate.
- True blackspots: no data means no PoC — the radio queues its GPS reports and reconnects automatically, but live voice is gone until signal returns. Teams working in genuine no-coverage environments should read the PoC vs conventional comparison, because this is the scenario where conventional still earns its keep.
Is 2G/3G switch-off a problem?
No — the opposite. UK 3G networks have already been retired and 2G is following; PoC rode that transition years ago because modern handsets are 4G-native with 5G arriving in premium models. If anything the switch-offs freed spectrum that improved 4G capacity, and every current-generation PoC radio sold in the UK is unaffected.
Next: Licensing: why PoC needs none — and when conventional does →