3 RF Design: SRM Radios 900MHz constants RF Path Loss with LOS: First mile: -96dB Each doubling of range: -6dB Transmitter Power: 1watt or 30dB Receiver Sensitivity: -108dB @ BER 1E-6 2.4GHz constants RF Path loss with LOS: First mile: -106dB Each doubling of range: -6dB Transmitter Power: 500milliwatts or 27dB Receiver Sensitivity: -108dB @ BER 1E-6
4 RF Design: Throughput Fact - Distance decreases throughput To maximize radio throughput and reliability: Maximize RF quality (shorter coax, higher gain antennas) If practical, dont use store-and-forward repeaters. Use back- to-back repeaters? Use point-to-point architecture To minimize system throughput requirements: Avoid cross-network data movement Only retrieve data once (Client/Server HMI model) Avoid HMIs as slaves Exchange data in large groups rather than several smaller groups (minimize protocol overhead) Minimize data needed and increase update period
5 RF Design: Antennas (1) Use radio manufacturer approved antennas Common types: Directional (yagi, parabolic) Omni-directional (di-pole) Gain is specified in dBd or dBi and achieved by directing (focusing) RF emission Emission patterns must be considered such that other sites are within focused area
7 RF Design: Coax (1) Data-Linc offers two piece coax assembles: Good price/quality ratio Flexibility at radio mount position Lightning protection ready Bulkhead pass-through ready Data-Linc only sells coax with end connectors that are inert gas welded, vapor sealed, and tested Do not cut to length! Coil excess
9 RF Design: Other RF Losses SMA and N-Type Connectors Loss:.5dB each junction Lightning Arrestors Always recommended for outdoor applications Install near equipment to be protected Loss:.1dB typical
10 RF Design: EIRP Effective Isotropic Radiated Power (EIRP) Set by government regulation This is maximum measured RF emission from an antenna In most countries not to exceed 4 watts Discussion: 1 watt can be increased to 4 watts by doubling the power twice (1w x 2 x 2 = 4w). A doubling of power equals 3dB, thus, doubling twice is 6dB. This means a 6dB gain antenna can be directly connected to a 900MHz radio to emit the maximum legal EIRP.
11 RF Design: Fade Margin This is the amount of RF signal strength exceeding the minimum needed for a specified receive sensitivity. Desired fade margin minimums: 20dB for SRM serial radios 30dB for SRM Ethernet radios
12 50 feet LMR400 50 feet LMR400 RF Path Theory Example 1 What is the fade margin – Will it work? 3dB Omni 3dB Omni 25 miles (40.2km) 30dB Transmit -108 dB Receive sensitivity