Guide to the WRC-1992 Diagram Calculator 1. Purpose of the WRC-1992 Diagram Calculator The WRC-1992 agreements introduced improved propagation models and interference criteria for VHF/UHF bands (especially 30–1000 MHz). The calculator implements the graphical coordination charts (Diagrams 1–6) from Annex 4 of the Final Acts. It helps engineers:
Compute minimum required separation distances between co-channel or adjacent-channel stations. Determine interference probability between analog TV/FM and new services. Assess compatibility with land mobile, fixed, and broadcasting services.
2. Key Input Parameters To use the calculator, you need the following (historical or current values for compliance): | Parameter | Description | |-----------|-------------| | Frequency band | Typically 174–230 MHz (Band III), 470–790 MHz (Bands IV/V) | | Service types | Broadcasting (TV/FM), Land mobile, Fixed | | Transmitter power (ERP) | Effective radiated power in dBW or watts | | Antenna heights | Above ground or above average terrain (HAAT) | | Polarization | Horizontal, vertical, or circular | | Desired/Interfering signal ratio | Protection ratio (e.g., 28 dB for analog TV co-channel) | | Propagation conditions | Percentage of time (usually 1%, 10%, 50%) | | Distance range | 10–600 km typical |
3. Working Principle (Diagram Lookup) The calculator emulates the WRC-1992 diagrams – nomographs relating field strength, distance, frequency, and time percentage. The main steps: wrc-1992 diagram calculator
Determine propagation curve Select the appropriate curve based on frequency, antenna height, and percentage of time (e.g., Curve 1 for 50% time, 100 m HAAT).
Find allowable interfering field strength E_int = E_desired - Protection ratio (dB)
Read coordination distance From the diagram, for the calculated interfering field strength and frequency, find the required separation distance. Guide to the WRC-1992 Diagram Calculator 1
Apply correction factors For polarization mismatch, terrain roughness, or adjacent-channel offset.
4. Example Calculation (Co‑channel analog TV, Band III) Given:
Frequency = 210 MHz ERP of interfering station = 20 dBW (100 W) HAAT (desired station) = 150 m Protection ratio = 28 dB Desired field strength at reference contour = 60 dBµV/m Time percentage = 10% 4. Example Calculation (Co‑channel analog TV
Steps with calculator:
Input frequency → selects diagram family. Enter ERP and antenna height → reference field strength at 1 km from interfering transmitter (e.g., 54 dBµV/m). Protection ratio → max allowable interfering field strength = 60 – 28 = 32 dBµV/m. Using WRC‑92 Diagram 3 (10% time, 150 m), find distance where field strength = 32 dBµV/m → approx. 180 km . Output = Minimum coordination distance = 180 km.