A 12-section interactive reference guide covering core radio communications topics used daily in RF and communications engineering design. Includes RF spectrum tables, LMR/P25 system design, in-building DAS (IFC 510/NFPA 1221), cellular/5G, microwave backhaul, satellite, propagation models, antenna engineering, ERRCS/BDA sizing, FirstNet, FCC licensing, and a complete quick-reference summary.
Each section targets a core radio communications discipline: RF spectrum and wave propagation fundamentals; Land Mobile Radio (LMR) system types including conventional, P25 Phase 1/2, DMR, and TETRA; in-building Distributed Antenna Systems (DAS) including passive, active, and public safety BDA systems under IFC Section 510 and NFPA 1221; cellular and 5G NR architecture (eMBB/URLLC/mMTC/massive MIMO/network slicing); microwave backhaul bands and link budgets; satellite orbits (LEO/MEO/GEO), VSAT, and GPS; RF propagation models (Okumura-Hata, COST-231, Longley-Rice) and Fresnel zone clearance; antenna types, coaxial cable loss tables, VSWR conversion, and EIRP calculation; ERRCS acceptance testing and BDA sizing; mission-critical communications including PSAP, NG911, FirstNet Band 14, and mutual aid channels; FCC licensing (Parts 90, 15, 101) and CBRS private LTE/5G; and a master quick-reference table.
Use the Prev / Next buttons at the bottom, or press the arrow keys on your keyboard. Click the ☰ menu button in the top-right to open the table of contents and jump to any section. The gold progress bar at the top tracks your position through all 12 sections. Mouse wheel scrolling advances through sections on the current slide.
Public safety in-building coverage requirements (IFC 510 / NFPA 1221) vary significantly by jurisdiction. The 95% floor coverage and −95 dBm signal level thresholds shown in this guide are the base IFC minimums. Many jurisdictions require higher signal levels (−85 dBm or stronger), additional backup power, specific BDA manufacturers, or system monitoring tied to the fire alarm panel. Always consult the AHJ and radio system administrator during the early design phase — not after construction.
Link budget calculations in this guide assume free-space path loss, which is the ideal case. Real-world links include additional losses from terrain (diffraction), building penetration, foliage, rain attenuation (above 10 GHz), and multipath. Always add at minimum 10–20 dB of fade margin beyond the calculated free-space link for non-line-of-sight paths, and 20–40 dB for critical communications infrastructure. For ERRCS/DAS design, build the distribution network to deliver −75 dBm at each service antenna to achieve −95 dBm at the portable radio accounting for body loss and interior shadowing.
IFC Section 510 (Emergency Responder Radio Coverage) requires that new buildings and significant renovations provide adequate radio signal strength for public safety personnel (fire, police, EMS) throughout the building. The threshold varies by jurisdiction but is commonly 50,000 square feet or buildings over 3 floors. The system must provide 95% coverage on every floor at a minimum signal level of -95 dBm. If the existing radio signal from outside is insufficient to meet this requirement, a Bidirectional Amplifier (BDA) system with a distributed antenna network must be installed. The system must be tested and accepted by the AHJ before occupancy and maintained with annual testing.
In a conventional system, users are assigned a dedicated frequency channel and must manually select it. If the channel is busy, they wait. This is simple but inefficient for large groups. In a trunked system (like P25 Phase 2 or Motorola SmartNet), a pool of channels is shared dynamically — users select a talk group, and the system automatically assigns an available channel from the pool when someone transmits. Trunked systems provide better spectrum efficiency, automatic roaming between sites, and management features. Public safety agencies almost universally use trunked P25 systems for coverage and interoperability.
Use the Friis free space path loss formula: FSPL(dB) = 20×log(d) + 20×log(f) + 32.44, where d is distance in kilometers and f is frequency in MHz. For example, a 1 km path at 900 MHz: FSPL = 0 + 59.1 + 32.44 = 91.5 dB. The link budget then becomes: EIRP (transmitter power + antenna gain - cable loss) − FSPL − other losses + receive antenna gain + receive cable loss = Received Signal Level (RSL). Compare RSL to the receiver sensitivity (e.g., -120 dBm) to get the fade margin. You want at least 20-40 dB of fade margin for reliable communications.
FirstNet uses Band 14 (700 MHz): 758–768 MHz downlink (base station to device) and 788–798 MHz uplink (device to base station). It is built on AT&T's nationwide LTE network with a dedicated core that provides priority and preemption for public safety subscribers. Priority means first responders' calls preempt commercial users when the network is congested. Preemption means during declared emergencies, PSAPs can force commercial users off to free up capacity for first responders. FirstNet is operated under a 25-year contract between AT&T and the First Responder Network Authority (FirstNet Authority), a federal agency within NTIA.