Wireless Radio Basics

Energy Losses / Gains In all wireless communication systems there are several factors that contribute to the loss / gain of signal strength. Things that affect the signal strength include: Choice of Cabling Antenna Selection Connectors Environmental Obstructions

Radio Bands and Channels : RADIO CHANNEL INCREASING FREQUENCY : RADIO BAND CHANNEL WIDTH :

Frequency Spectrum Basic resource for wireless communications practical radio communication between 3 KHz and 300 GHz new systems designed tend to go higher in frequency providing larger bandwidth

Spectrum Allocation Chart Mobile bands Upper part of band for base Tx lower part of band for base Rx

Radio Bands for Industrial Wireless Licensed band - licensed by government authority Specific frequency channel, only one user per area “Narrow-band” - channel width 6.25, 12.5 or 25KHz License-free - ISM - Industrial, scientific & medical Spread spectrum technique, Allows wide-bandwidth

Radio Bands for Industrial Wireless -example Examples Licensed band - 450 to 470 MHz - 1600 x 12.5KHz License-free - 902 to 928 MHz, 26 x 1MHz or 1040 x 25KHz 2.4 - 2.48 GHz, extremely wide channels Wider channels  Wider bandwidth  Higher data rates

Types of Spread Spectrum Direct Sequence (DSSS) Spreads data packet over wide band - effectively transmitting each bit on many channels. Higher data rates (> 1Mb/s), but vulnerable to interference. Frequency Hopping (FHSS) Change frequency after each data packet. Slower data rates (115.2Kbd), but more robust. Less vulnerable to interference.

Direct Sequence SS Each data bit is spread over multiple frequencies Average power is reduced Direct Sequence has a higher bit rate than Frequency Hopping More vulnerable to interference

Frequency Hopping Power Watt Frequency Time/mSec 928MHz 869.65 MHz Here it is in action verses time! Frequency 902MHz 869.4 MHz Time/mSec

Frequency Hopping 905U uses 50 x 250KHz channels After 3 transmissions

Frequency Hopping After 12 transmissions

Frequency Hopping After 100 transmissions, all channels have been used once

Radio Variables Two main variables Frequency - Hertz - KHz, MHz, GHz Power - linear measurement - Watts - mW, W - log scale more common - dBm - referenced to 1mW dBm = 10 log10 [RF signal in mW] x 2 = +3dB x 4 = +6dB x 5 = +7dB x 10 = +10dB x 1/2 = -3dB x 1/4 = -6dB x 1/5 = -7dB x 1/10 = -10dB 1mW = 0dBm 10mW = 10dBm 100mW = ? 200mW = ? 20dBm 23dBm

The real question should be: How far will a radio receive? How far will the radio transmit? The answer is... The real question should be: How far will a radio receive?

Receiver Sensitivity A radio signal becomes unreliable when it’s strength falls below the Receiver Sensitivity or the background noise RF Amplitude Time Noise Average level Receiver sensitivity

Bit Error Ratio BER - Ratio of the number of errors to total bits transmitted RF Amplitude Time Noise Receiver sensitivity High BER Low BER Received signal

Fade Margin Fade margin is margin between Signal and Noise / Sensitivity “Safety Margin” - normally 10dB on a “fine day” RF Amplitude Time Noise Receiver sensitivity Fade margin Received signal

Factors Affecting Distance Frequency as frequency increases, distance decreases proportionally Receiver sensitivity, antenna gain, cable loss despite manufacturers’ claims, most wireless products have similar sensitivities Noise / interference The noisier the environment the more careful you have to be with antenna placement Transmitter power, antenna gain, cable loss Attenuation of radio signal Heights of antennas, Obstructions in radio path Other factors Atmospheric, Ground Mineralisation

Signal Attenuation A radio signal attenuates as it passes through air Transmitter 30dBm = 1W RF Power (dBm) along a radio path Min. signal level for reliable operation Receiver -110dBm = 0.01pW Distance

Transmit Power RF Power (dBm) along a radio path Distance Increasing the power at the transmitter increases the distance In “free-space”, distance doubles for 4x increase in power (+6dB) Power must reduce to 1/4 (-6dB) for distance to halve Transmitter RF Power (dBm) along a radio path Min. signal level for reliable operation Distance

The effect of obstacles 10 - 20 miles RF Power (dBm) along a radio path Typical congested industrial path Line-of-sight path 1000 - 3000 feet Distance

The effect of obstacles An obstacle has less blocking effect in the middle of the path than close to one end Radio path pattern between two antennas is a “football” envelope The envelope is “less spread” as frequency increases  obstacles have more of a blocking effect at higher frequencies

Typical industrial radio path No direct path Multiple reflected paths Tx There is more signal loss on reflection or passing through buildings as frequency increases Rx

Radiated Power Transmitter power = Power generated by transmitter Radiated power = Power radiated by antenna in desired direction ERP = Effective Radiated Power = Transmitter power * Antenna gain * Cable loss Cable loss is less than 1 and reduces radiated power. Antenna gain should be more or less than 1 In dB terms, ERP = Transmitter dBm + Antenna gain dB - Cable loss dB

Radiated Power Same effect at Receiver Effective radiated Transmitter Power = 30dBm = 1W Effective radiated power = 36dBm = 4W cable loss - 4dB Antenna gain = 10dB Signal at Receiver = -94dBm cable loss - 4dB Received Signal = -100dBm Antenna gain = 10dB Same effect at Receiver

Power Losses All wireless communication systems have several factors that contribute to the loss of signal strength. Cabling, connectors, and lightning arrestors can all impact the performance of your system if not installed properly. In a ‘low power’ system every dB you can save is important!! Remember the “3 dB Rule”. For every 3 dB gain you will double your power For every 3 dB loss you will halve your power

3 dB Rule -3 dB = 1/2 power -6 dB = 1/4 power +3 dB = 2x power Sources of loss in a wireless system: free space, cables, connectors, jumpers, obstructions

Propagation Mechanisms Propagation mechanisms are very complex and diverse. First, because of the separation between the receiver and the transmitter, attenuation of the signal strength occurs. In addition, the signal propagates by means of diffraction, scattering, reflection, transmission, refraction, etc.

Propagation Mechanisms - LOS (Line of Sight) Site A Site B Antenna to Antenna This maximizes the distance and reliability of the signal.

Propagation Mechanisms - Diffraction Diffraction occurs when the direct line-of-sight (LOS) between the transmitter and the receiver is obstructed by an obstacle whose dimensions are much larger than the signal wavelength (67cm for 450 MHz radio wave). Waves bend around the obstacle, even when LOS does not exist Site A Site B

Propagation Mechanisms - Scattering Scattering occurs when the path contains obstacles that’s are comparable in size to the wavelength (67cm for 450 MHz radio wave). E.g., foliage, street signs, lamp posts Similar to diffraction, except that the radio waves are scattered in a greater number of directions. Of all the mentioned effects, scattering is the most difficult to be predicted. Site A Site B

Propagation Mechanisms - Reflection Occurs when the radio wave encroaches an obstacle which is larger than the wavelength (67cm for 450 MHz radio wave). A reflected wave can increase or decrease the signal level at the receiver. In many cases, the received signal level tends to be very unstable. This is commonly referred to as Multipath Fading. E.g., the surface of the Earth, buildings, walls, etc. Site A Site B

Penetrating Objects 900Mhz 2.4Ghz Higher frequencies have higher attenuation on penetrating obstacles 900Mhz 2.4Ghz

Reflections 900Mhz 2.4Ghz Higher frequencies lose more signal strength on reflection

Effects of Obstructions Radio path does not have to be line-of-sight - only for maximum range Obstacles reduce radio signal, witch reduces reliable range Metal and wet obstacles reduce signal more than non-metal and dry An obstacle has more affect when it is closer to the antenna TEST THE RADIO PATH

Antennas - How They Work The antenna converts radio frequency electrical energy fed to it (via the transmission line) to an electromagnetic wave propagated into space. The physical size of the radiating element is proportional to the wavelength. The higher the frequency, the smaller the antenna size. Assuming that the operating frequency in both cases is the same, the antenna will perform identically in Transmit or Receive mode

Antenna Pattern Reference - Isotropic Antenna Isotropic Source - spherical radiation This is a hypothetical point source antenna that serves as a reference for the measurement of antenna gain Gain = 0 dB Elevation View Plan View

Antenna Types Omni-Directional The type of system you are installing will help determine the type of antenna used. Generally speaking, there are two ‘types’ of antennas: Omni-Directional This type of antenna has a wide beamwidth and radiates 3600; with the power being more spread out, shorter distances are achieved but greater coverage attained Dipole antenna This type of antenna is typically used for shorter distances

Light is omni-directional Omni Antenna - Example Light is omni-directional

Omni Antenna Radiation Pattern Horizontal Pattern Vertical Pattern

Dipole Antenna Dipole Pattern Isotropic Pattern Dipole is made of two 1/4-wave conductors joined in the middle Elevation Gain = 2.14 dB Plan

Collinear Antenna Collinears Dipole Collinear 2 Dipoles Stacked Dipole

Typical Omni Antenna Gains Dipole Whip 2dB Collinears 5 / 8 / 10 dB 1/4 wave whips -3 to 0dB

Antenna Types Directional This type of antenna has a narrow beam-width; with the power being more directional, greater distances are usually achieved but area coverage is sacrificed Yagi, Panel, Sector and Parabolic antennas This type of antenna in is used in both Point to Point and Point to Multipoint

Light is focussed in a particular direction Typical Omni Antenna Gains YAGI Antennas Reflector / mirror Light is focussed in a particular direction

YAGI Antennas Reflector Folded Dipole Director

YAGI Radiation Pattern

2 Element YAGI Isotropic Antenna Gain = 3 dB

YAGI Bandwidth Yagi Antennas direct almost all power in one direction Higher gain antennas direct power into a tighter beam 6 Element Yagi 450 9 Element Yagi 350

Typical YAGI Gains 16 Element 16dB 9 Element 14dB 6 Element 11dB

Parabolic, Grid-pack Antennas only for very high frequency > 2 GHz used in medium to long links gains of 18 to 28 dBi

Sectoral Antennas directional in nature, but can be adjusted anywhere from 450 to 1800 typical gains vary from 10 to 19 dBi very commonly seen at cell phone base stations

Antenna Polarization Polarization can be Vertical or Horizontal - depend on how antenna is installed. Omni-directional antennas have Vertical polarity when mounted vertically Polarity of Yagis is based on direction of elements - can be Vertical or Horizontal All antennas in the same RF network must be polarized identically regardless of the antenna type.

Polarity - Vertical Yagi Omni-directional

Horizontal Polarity is known as ‘E’ Plane Polarity - Horizontal Horizontal Polarity is known as ‘E’ Plane Two Yagis can form a Horizontal polarity link Not compatible with Omni-directional antennas Can be used for “radio isolation” from another system with Vertical polarity

Coaxial Cables Data wireless uses 50 ohm cables - RF impedance is based on inner : outer diameters Loss increases with cable length and frequency Larger diameter cables have lower loss, but are much harder to install - bending radius

Attenuation Table - Cables Attenuation Table for 900Mhz should be added too as follows: -12.9dB/100meters (LMR-400) -8.3dB/100meters (LMR-600) -4.1dB/100meters (7/8” Heliax) -7.55dB/100meters(1/2” Heliax)

Connector Types N-male BNC N-female SMA

Connectors – Good Practices Have someone experienced install them Poor fitting results in high RF losses Best to buy pre-made cables Do not splice connections in the antenna lines Buy one cable that reaches the entire distance Exposed connections need to be well taped Antennas – usually Female Lightning Arrestors – usually Female

Cable Connection Protection Stretch to elongate sealant tape while wrapping over the connection Scotch® 23 Rubber Splicing Tape For proper UV protection Electrical Tape should then be wrapped over the Vulcanising Tape All outside coax connections should be wrapped in a Rubber Vulcanising Tape to stop moisture ingress.

The Lightning Arrestor Use a lightning arrestor when the antenna is not protected by surrounding steelwork Connect antenna bracket, wireless unit and the lightning arrestor to same earth point. Typically structural steel is OK for ground connection Do not use Gas Lines or Water pipes for discharge. Check Electrical Code for grounding recommendations.

Redundancy This is one of the main concerns with wireless systems. Our products do support redundancy for Radio path I/O Total redundancy Stand-by

Wireless Redundancy – Radio Path Radio Path redundancy between same modules via a repeater Suitable if primary radio path is variable – e.g. construction site Simple to achieve, and only need one radio channel Doesn’t protect equipment failure Two sets of outputs Two comms-fail outputs - one for each path Radio Path Redundancy

Wireless Redundancy – Outputs Redundancy for outputs in different locations Suitable when connected to common system via existing LAN Protects equipment failure & RF interference at output module Doesn’t protect equipment failure at input end Output Redundancy input

Wireless Redundancy – Total Complete redundancy Two separate wireless systems on two separate radio channels Protects equipment failure and RF interference at both ends Special set-up to ensure radio channels don’t “block” each other Hot Redundancy

Wireless Redundancy – Standby Standby Redundancy Protects equipment failure, but not RF interference Intelligent devices (e.g. PLC) must be at both ends Intelligent device switches power upon comms-fail Standby Redundancy input comms-fail output

Rules For Best Performance Line of Sight whenever possible – Always the best Antenna outside of the cabinet - Always Antenna away from Noisy sources – As far away as possible other antennas, VFDs, Welders, computers, etc Antenna as high as possible Coax Cable as short as possible Use pre-made tested hi-quality cables, this will lower the loses in the system Ground ALL equipment to the earth system properly This will reduce the noise level