Avlite AvMesh User manual

V1.0
INSTALLATION & TROUBLESHOOTING GUIDE
AvMeshTM
RF Communications Systems

2
Version No. Description Date Author Reviewed Approved Design
1.0 Manual Launch April 2019 P. Naidu J. Ohle W. Evans M. Sugars

AvMesh® RF Communications Systems
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Table of Contents
1.0 Glossary of Terms.......................................................................................................................5
2.0 Background..................................................................................................................................6
3.0 RF Fundamentals ........................................................................................................................ 7
3.1 Elements of a Radio Frequency communications system........................................................................7
3.2 Modulation and Demodulation.................................................................................................................................. 8
3.3 Intermodulation.................................................................................................................................................................. 8
3.4 Antennas................................................................................................................................................................................ 9
3.4.1 Gain................................................................................................................................................................................10
3.4.2 Direction......................................................................................................................................................................10
3.4.3 Polarization................................................................................................................................................................. 11
3.5 RF Propagation................................................................................................................................................................... 11
3.5.1 Line-of-sight propagation..................................................................................................................................12
3.6 Interference.........................................................................................................................................................................13
3.6.1 Fresnel zones............................................................................................................................................................13
3.6.2 In-band interference............................................................................................................................................15
3.7 Spectrum Analyzers.......................................................................................................................................................16
3.7.1 Types of Spectrum Analyzer...........................................................................................................................16
3.7.2 The Decibel formula............................................................................................................................................. 17
3.7.3 Signal to Noise Ratio (SNR or S/N)...............................................................................................................19
4.0 AvMeshTM Communications System: Theory of Operation...............................................20
4.1 Node Information............................................................................................................................................................. 20
4.2 Network set-up procedure.........................................................................................................................................21
4.3 Network bridging ............................................................................................................................................................24
5.0 Avlite Wireless Remote Controller.........................................................................................27
5.1 Radio Controller Menu................................................................................................................................................... 27
5.1.1 Operation Mode....................................................................................................................................................... 27
5.1.2 Advanced Op Mode.............................................................................................................................................28
5.1.3 Light Group ...............................................................................................................................................................28
5.1.4 Intensity .......................................................................................................................................................................28
5.1.5 Timeout Mode.........................................................................................................................................................28
5.1.6 Timeout Duration...................................................................................................................................................29
5.1.7 Diagnostic...................................................................................................................................................................29
5.2 Controller Menu (Advanced).................................................................................................................................... 30
6.0 Direct Connection...................................................................................................................... 31
6.1 To force a primary node ...............................................................................................................................................31
7.0 Rotary Switches ........................................................................................................................32
7.1 To force a Reserve node...............................................................................................................................................32
8.0 Maintenance/Housekeeping of the AvMeshTM Communications System ......................32
9.0 Troubleshooting ........................................................................................................................33
9.1 Identifying the Problem.................................................................................................................................................33
9.2 Single Fixture Non-functional...................................................................................................................................34
9.3 Whole Runway Non-functional...............................................................................................................................35
9.4 Multiple Fixtures Non-functional.............................................................................................................................36
9.4 Multiple Fixtures Non-functional Continued ....................................................................................................37

4
Table of Figure
Figure 1: Hub and Spoke architecture (left) and Mesh Network (right) .................................. 6
Figure 2: Radio Communications System.................................................................................................7
Figure 3: Wavelength is inversely proportional to frequency.......................................................7
Figure 4: Creation of intermodulation products ................................................................................... 9
Figure 5: Radiation pattern of Isotropic (left) and Dipole (right) antennas ..........................10
Figure 6: Unidirectional (left), Bi-directional (center) and Omnidirectional (right)
antennas......................................................................................................................................................................10
Figure 7: Vertically (left) and Horizontally (right) polarized antennas...................................... 11
Figure 8: The first (red), second (green) and third (blue) Fresnel zones between the
transmitting and receiving antennas ......................................................................................................... 14
Figure 9: The first node to turn on will become a primary node............................................. 21
Figure 10: The nodes are configured as primary if they are not within range of at
least 3 other primary nodes........................................................................................................................... 22
Figure 11: If the node is within range of at least 3 other primary nodes, it will
become a reserve node.................................................................................................................................... 22
Figure 12: If a node is within range of at least 3 other primary and 3 other reserve
nodes, it will remain as a listen only node.............................................................................................. 23
Figure 13: Resulting mesh network .......................................................................................................... 23
Figure 14: Creation of 2 different network IDs, one at each end of the runway ............ 24
Figure 15: The next nodes to turn on will be independent of the nodes at the other
end of the runway................................................................................................................................................ 25
Figure 16: Node 5 will become a primary node in network 4 if node 9 accepts the
bridging....................................................................................................................................................................... 25
Figure 17: Other primary nodes within range of node 5 will also join the new
network....................................................................................................................................................................... 26
Figure 18: All primary nodes will adopt the better network....................................................... 26

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1.0 Glossary of Terms
Attenuation - The negative ratio of the output power to the input power in decibels
(dB). It is the reduction in power of a signal as it propagates through space.
Carrier signal - a pure wave of constant frequency, amplitude and phase.
Centre frequency - The central frequency of a filter or channel, centered between the
upper and lower cutoff frequencies.
Fresnel Zone - A theoretical elliptical region between the transmitting and receiving
antennas. The size of the ellipse is determined by the frequency of operation and the
distance between the transmitter and receiver. If 80% of the first Fresnel Zone is free of
obstacles, the propagation loss is said to be equivalent to free space loss.
Gain - The positive ratio of the output power to the input power in decibels (dB).
Interference - Any external factor (such as physical obstacles, noise or other radio
signals) that degrade or reduce the clarity of the desired radio signal.
Light group - A way to group lights in an area so that they can be controlled in unison.
This allows the airfield to independently control different areas such as multiple run-
ways, taxiways and helipads.
Listen only light - A light that will receive commands and act upon them, but will not
pass the commands on.
Mesh network - A local network architecture in which the nodes connect to as many
nodes as possible and cooperate with one another to transfer data from point to point.
Noise floor - This is the measure of signal created from noise sources and unwanted
signals, with noise defined as a signal other than that being monitored. It may include
atmospheric noise, thermal noise and cosmic noise.
Passband - The range of frequencies that can pass through a filter without attenuation.
Primary Node - A light that is part of the primary AvMeshTM network. This light will
receive commands from a controller, other primary node or a reserve node. This light
will act upon the commands and pass them on to other nodes in the network.
Reference level - The top most line in the spectrum analyzer display.
Reserve node - A light that is part of the reserve AvMeshTM network. This light will
receive commands from a controller, a primary node or another reserve node. This
light will act upon the commands and pass them on to other nodes in the network.
RF Propagation - The behavior in which radio waves travel from one point to another.
Sensitivity - The smallest signal that can be detected by the receiver.
Selectivity - The ability of a receiver to differentiate between signals that are close
together in frequency.
Span - The range between the measured start and stop frequencies.
Spectrum analyzer - An electronic measurement device that helps to determine the
type and frequencies of interfering RF signals.
Transmit Power - The power that is input to the antenna cable, before cable loss and
antenna gain are considered.

6
2.0 Background
The AvMeshTM Communications System is a wireless communication platform which
operates by broadcasting signals from the Avlite wireless remote controller to the lights in
the system via a 2.4GHz encrypted mesh network.
A typical network architecture (e.g. networks used to connect devices such as phones,
computers and routers) uses a ‘hub and spoke’ arrangement in which points on the
network (the spokes) are all connected to a single center device known as the hub. The
hub serves as an access point through which all devices in the network connect to one
another. This architecture is not as flexible as a mesh network.
Instead of connecting to all other devices through a single centralized point, the lights, also
known as nodes, act as centralized points and connect to all other nodes that are nearby
in the mesh network. The nodes send signals to other nodes that are within range and
the signals are passed from node to node until the final destination is reached. This allows
all the lights in the system to be controlled wirelessly, even if the final destination is out of
range of the wireless controller.
Figure 1: Hub and Spoke architecture (left) and Mesh Network (right)
The AvMeshTM Communications System is self-realizing meaning that once deployed, the
airfield lights will undertake a period of network mapping, whereby the system determines
how many lights need to repeat commands and be ‘nodes’ to provide the airfield enough
coverage.
The sections in this manual cover the necessary fundamentals of Radio Frequency
(RF) Communication Systems to provide an understanding of how the AvMeshTM
Communications System operates as well as provide troubleshooting information relating
to the AvMeshTM Communications System.

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3.0 RF Fundamentals
3.1 Elements of a Radio Frequency communications system
A typical radio frequency communication system consists of the following elements:
• Transmitter - Feeds the signal to a transmitting antenna by first encoding the data
into RF waves (signals) with a certain signal strength (known as the power output) to
project the signal to the receiver.
• Receiver - Accepts and decodes the RF signals that come through the receiving
antenna and rejects unwanted ones via the use of a filter.
• Environment - The physical space between the transmitter and receiver over which
the radio waves propagate. The environment through which communication is
occurring can be affected by interference and physical obstructions such as walls,
buildings and vegetation.
• Antennas or other focusing elements - Devices that focus the radio frequency
energy in a particular direction.
Figure 2: Radio Communications System
In radio frequency communication, electromagnetic waves (signals) are created and
radiated from a source (i.e. transmitting antenna at the transmitter) and then travel through
the air at the speed of light after which they are picked up at a particular destination (i.e.
receiving antenna at the receiver). The higher the frequency of an electromagnetic wave
(signal), the shorter the wavelength. Signals with longer wavelengths are typically able
to travel a greater distance and bend around objects better than signals with shorter
wavelengths.
Figure 3: Wavelength is inversely proportional to frequency
Transmitter
Receiver
Transmitter
Receiver
Transmitting
Antenna
Receiving
Antenna
Env ir on me nt
Transmitter
Receiver
Transmitting
Antenna
Receiving
Antenna
Env ir on me nt
Lower frequency-
longer wavelength
Lower frequency-
longer wavelength
Higher frequency-
shorter wavelength
Higher frequency-
shorter wavelength
Higher frequency-
shorter wavelength Lower frequency-
longer wavelength
Lower frequency-
longer wavelength
Higher frequency-
shorter wavelength
Higher frequency-
shorter wavelength
Higher frequency-
shorter wavelength

8
3.2 Modulation and Demodulation
Modulation occurs in the transmitter, where the input signal (also known as the modulating
signal) is intentionally ‘mixed’ with a sinusoidal carrier wave (a wave of constant frequency,
amplitude and phase). Through this process, one of the three parameters (i.e. amplitude,
frequency or phase) of the carrier wave is modified by the input signal according to a
predefined method known as the modulation technique. This encodes the carrier wave
with the required information from the input signal before the carrier wave is transmitted
to the receiver. The information contained in the input signal is able to travel over a much
larger distance when encoded into the carrier wave.
After the modulated carrier wave is received and amplified by the receiver, the transmitted
information is extracted from the carrier wave through a process known as demodulation.
The type of demodulation used to remove the carrier wave depends on the technique
used during modulation. It is important to note that the receiver must be able to identify
the received modulated carrier signal from other signals which may be using the same
channel.
For a two-signal input into a modulator (or non-linear mixer or amplifier), an input signal
of frequency f1 is mixed with a carrier signal (or other competing signal) of frequency
f2. These signals will be present at the output along with additional signals called
intermodulation products which are at the sum and difference and integer multiples of the
original frequencies. The frequencies of the intermodulation products can range in order
from second order (e.g. 2f1, 2f2, f1-f2 or f1+f2), third order (e.g. 3f1, 3f2, 2f1-f2, 2f1+f2, 2f2-f1,
2f2+f1), fourth order (e.g. 4f1, 4f2, 2f2+2f1,2f2-2f1,2f1+2f2, 2f1-2f2) up to the nth order and
usually arise from non-linearity in the signal processing equipment.
When many transmitters are placed at the same location, intermodulation may become
an issue. Typically, it is the third odd order intermodulation products which are of most
concern because they are the closest in frequency to the fundamental frequencies and
therefore cannot be effectively filtered out of the system (although this is not limited to
only third order products). This results in a spectrum of products that are spread out either
side of the fundamental frequencies which increases the bandwidth of the signal. In some
cases, the bandwidth of the signal is increased to a degree where it causes sideband
splatter in which the channels either side of the operating frequency are impinged by the
wider bandwidth of the signal. This causes interference with other systems operating in
these directly adjacent channels, otherwise known as co-channel interference.
3.3 Intermodulation

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Figure 4: Creation of intermodulation products
Furthermore, the third order intermodulation products can potentially pass through the
receiver since they are close in frequency to the fundamental frequencies. Consider the
situation in which 3 signals are present at the input of a non-linear amplifier or mixer; one
is the signal of interest at frequency f3 (e.g. 140 MHz) and the other two are competing
signals at frequencies f1 (e.g. 100MHz) and f2 (e.g. 120MHz). There are 15 combinations
of third order intermodulation products (including harmonics) from the interactions
between the signal of interest (f3) and the competing signals (f1 and f2). One of these
intermodulation products (i.e. 2f2-f1=2x120 – 100=140MHz) is equal to the frequency of the
signal of interest (f3) and as a result, this intermodulation product will enter the receiver
and interfere with the signal of interest. As a consequence, the receiver is at risk of
extracting and processing the incorrect information.
It is therefore essential to calculate the 3rd order harmonics and intermodulation products
for all combinations of competing frequencies in a site to determine if there is a possibility
of interference.
Antennas are a key component of any radio frequency communications system as they
enable the transfer of information from the transmitter to the receiver. For this reason, poor
antenna performance limits the performance of the overall system.
Antennas provide a radio communication system with three main properties; gain,
direction and polarization. A description of each is given in the following sections.
Typically, antennas do not transmit or receive radio frequency energy uniformly in all
directions and instead, transmit or receive more in some directions compared to others.
The antenna gain can be defined as a ratio of the highest signal strength transmitted or
received in a particular direction to that of a reference antenna. The two main types of
reference antenna are either the isotropic antenna which radiates the radio frequency
energy uniformly in all directions or the dipole which does not.
f1-f2
f1 f2
Frequency
Amplitude
2f1-f2
2f2-f1
2f1
f1+f2
2f2
3f1
2f1+f2
f1+2f2
3f2
f1-f2
f1 f2
Frequency
Amplitude
2f1-f2
2f2-f1
2f1
f1+f2
2f2
3f1
2f1+f2
f1+2f2
3f2
3.4 Antennas
3.4.1 Gain

10
Figure 5: Radiation pattern of Isotropic (left) and Dipole (right) antennas
A higher gain typically indicates that the signal (transmitted or received) is concentrated
over a smaller beam width and can therefore cover a larger distance. However, the
effectiveness of a high gain antenna depends on the application. Typically, a high gain
antenna is most suitable for applications where the source or destination of the signal is
known in order to isolate a specific signal and avoid external interfering signals.
A lower gain typically indicates that the signal (transmitted or received) covers a wider
beam width and hence, a wider area. A low gain antenna is generally most suitable for
applications where either the source or the destination of the transmitted signal is not
known and hence, coverage in all directions from the antenna is required.
Antennas operate by concentrating the radio frequency energy they radiate or receive in
a beam of a particular width. The width of the beam is known as the antenna direction or
directivity.
The directional qualities of an antenna are known as being either unidirectional, bi-
directional or omnidirectional and each possesses its own coverage capabilities. A
unidirectional antenna is able to transmit or receive radio frequency energy in one
particular direction whereas a bi-directional antenna is able to do so in two particular
directions. An omnidirectional antenna is able to transmit or receive radio frequency
energy equally in all horizontal directions and is therefore able to achieve 360-degree
coverage.
Figure 6: Unidirectional (left), Bi-directional (center) and Omnidirectional (right) antennas
3.4.2 Direction

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An electromagnetic wave is made up of an electric field and magnetic field that oscillate
perpendicular to each other. Polarization of the electromagnetic waves refers to the plane
in which the electric field is oscillating. Although there are many forms of polarization, the
electric field is often polarized in either the vertical direction or in the horizontal direction
and this is dependent on the antenna orientation in relation to the earth.
Similar to electromagnetic wave polarization, the most common forms of antenna
polarization are vertical and horizontal. A vertically polarized antenna transmits and
receives vertically polarized signals best whereas a horizontally polarized antenna
transmits and receives horizontally polarized signals best. Antenna polarization is an
important factor to consider as antennas are most effective when they are polarized in the
same direction as the received electromagnetic waves (signals). If the polarization of the
antenna and received signal do not match, a corresponding decrease in the received signal
level will occur.
Once a signal has been transmitted, its polarization should remain the same. However,
reflections, refractions and diffractions occurring between the receiver and transmitter
can slightly change the polarization of the signal and this has the potential to degrade the
received signal level.
Figure 7: Vertically (left) and Horizontally (right) polarized antennas
The way in which radio waves (signals) travel from one point to another is called RF
propagation and is an essential aspect of how radio communications systems operate (i.e.
how the radio signals travel from the transmitter to the receiver). RF propagation is greatly
affected by the environment in which the radio waves travel as well as the various objects
that may appear in the transmission path. It is the transmission path that governs the level
and quality of the received signal.
There are a number of categories into which RF propagation can be placed and these are
dependent on the frequency of radio waves involved in the radio communications system.
A brief description of the main categories of RF propagation are shown below.
Avlite products (2.4 GHz) operate at frequencies in the Ultra high frequency (UHF) range
of the radio spectrum. The main type of RF propagation in this frequency range is line-of-
sight propagation.
3.5 RF Propagation
3.4.3 Polarization

12
3.5.1 Line-of-sight propagation
Line of sight propagation (also known as free space propagation) is the most common
mode of propagation for radio waves in the Very High Frequency (VHF) section and above
of the radio spectrum. The radio waves travel in a direct path, propagating outwards from
the transmitting antenna towards the receiving antenna at the speed of light, with the
signal strength reducing as it moves further away from the transmitter. This is known as
Free Space Path Loss and assumes no reflections or obstacles between the transmitter
and receiver.
The rate at which the signal strength falls is shown by the equation below:
Where ‘k’ is a constant and ‘d’ is the distance from the transmitter. This formula indicates
that the rate at which the strength of a signal falls as it travels further away from the
transmitter is inversely proportional to the square of the distance from the transmitter.
For example, the strength of the signal at two meters away from the transmitter will be a
quarter of the signal strength at one meter away from the transmitter.
The basic formula above can be altered to take into account other factors that can
influence the radio signal.
The formula for Free Space path loss is shown below:
Where:
d = Distance between antennas in meters
f = Frequency in Hertz
GTx = Gain of transmitting antenna
GRx = Gain of receiving antenna
c = Speed of light in vacuum in meters per second (i.e. 3 x 108 m/s)
It is important to note that this formula provides only an estimation of signal loss through
free space as reflections or obstacles are not considered. This value can be used to
calculate the RF Link Budget, which is a summary of the transmitted power with all the
gains and losses in the system and provides an estimation of the strength of the received
signal. Depending on the estimated strength of the received signal, the transmitted power
and antenna gains can then be adjusted accordingly. It is essential for the link budget to
be calculated during planning of a radio communications system to ensure that the signal
strength is sufficient to allow the system to meet its operational requirements once it is
installed.

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The AvMeshTM Communications system uses the Avlite wireless remote controller as well
as the lights themselves as transmitters. It is therefore essential to consider the impact of
the following on the RF propagation:
• Range of the lights
• The distance between each light (node) in the system
• The distance from the control tower to the first light (node) on the runway (or
applicable area)
It is important to note that this type of propagation requires the transmitter and receiver
to be in view of each other without any form of obstacle (e.g. terrain, vegetation, buildings,
transmitter towers etc.) between them.
However, even if a direct line of sight does exist between the transmitter and receiver
(i.e. clear of obstacles), the signal strength may still not be strong enough. Geographical
obstacles near the direct path between the transmitter and receiver as well as the
curvature of the earth can also have an effect on the ability of the signal to propagate.
Hence, the area of clearance required for good connection is not uniform, but rather an
elliptical region between the transmitting and receiving antennas known as the Fresnel
zone. (See section 3.6.1 Fresnel zones for more information).
Interference can be defined as any external factor (such as physical obstacles, noise or
other radio signals) that degrade or reduce the clarity of the desired radio signal.
The conditions that result in interference are unique to each individual environment and
therefore, there is no standard level of interference nor is there a single formula to calculate
or quantify it.
In point to point wireless communication systems, it is important for the line of sight
between the transmitter and receiver to be free of any obstructions to enable ideal RF
propagation. However, it is important to note that an obstruction-free line of sight will not
always provide a perfect connection. There is also a requirement for the clearance of what
is known as the Fresnel zone, which is a series of concentric ellipsoidal regions between
the transmitting and receiving antennas that have constructive and destructive effects on
the waves that are reflected, refracted or diffracted within them.
The size of the Fresnel zone is governed by the frequency of operation and the distance
between the transmitting and receiving antennas.
There are an infinite number of Fresnel zones, however, the first three zones usually have
a notable effect on RF propagation, with the first Fresnel zone being the most significant.
This is because the strongest signals lie closest to the direct line of sight path between the
transmitter and receiver.
3.6 Interference
3.6.1 Fresnel zones

14
Figure 8: The first (red), second (green) and third (blue) Fresnel zones between the
transmitting and receiving antennas
Obstacles in the Fresnel zones can cause some of the radio waves to be reflected,
refracted or diffracted before they arrive at the receiving antenna. Reflection occurs when
the propagating radio wave comes into contact with a large object (e.g. buildings, walls,
mountains etc.) that is larger than the wavelength of the transmitted wave. Refraction
occurs in response to changes in the refractive index of the medium in which the radio
waves are propagating. Small changes of refractive index mainly occur in the atmosphere
where the refractive index of air is higher closest to the surface of the Earth. The radio
waves are refracted towards the area of higher refractive index and hence, the wave
propagation falls slightly in height. Diffraction occurs when the propagating waves come
into contact with a sharp edge such as a wall edge or mountain ridge. All three phenomena
cause the original path of the radio waves to be altered.
These altered paths are longer than the direct line-of-sight path and hence, they will take
a longer amount of time to reach the receiver compared to the waves that have travelled
in the direct path. This difference in time and path length causes a phase change of the
radio waves in the altered paths and they can arrive either in phase or out of phase with
the waves that travel directly to the receiver. When the waves combine at the receiving
antenna, the resulting signal can be either diminished or unaffected depending on the
number of the Fresnel zone in which the reflection, refraction or diffraction has occurred.
Reflections that occur in odd numbered Fresnel zones (i.e. zone 1,3 etc.) cause a 360°
phase shift of the radio waves that travel in the alternate paths. The resulting waves are
still in phase with the signals from the direct path and as a result, they will combine in a
constructive manner and result in no effect on the received signal. Similarly, reflections
that occur in even numbered Fresnel zones (i.e. zone 2 etc.) cause a 180° phase shift of
the radio waves from the alternate paths which are detrimental to RF propagation as the
waves from the direct and alternate paths will combine in a destructive manner and result
in signal loss. This is also known as Multipath fading as the transmitted radio waves have
arrived at the intended receiver (or node) via multiple paths due to reflection, refraction and
diffraction.
1st
2nd
3rd
1st
2nd
3rd
Line of sight path
1st
2nd
3rd
Line of sight path

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The radius of the Fresnel zone increases as the distance between the transmitter and
receiver increases. Because of this, the curvature of the Earth can potentially impeach the
Fresnel zone and therefore cause signal loss.
In order to optimize the signal strength at the receiver, it is best to minimize the number of
out of phase signals reaching the receiving antenna by ensuring that the strongest signals
(i.e. in the first Fresnel zone) do not come into contact with obstacles. As a general rule of
thumb, the 1st Fresnel zone (the area from the line of sight to the outer boundaries of the
1st Fresnel zone) must be at least 60% clear in order to maintain a satisfactory connection.
The AvMeshTM Communications System operates in the unlicensed 2.4GHz ISM band.
Because of their cost-effectiveness, easy set-up and easy maintenance, unlicensed bands
are a popular choice for many other systems as well. Consequently, this makes them
susceptible to interference from other users operating on the same ISM band in the same
area, giving rise to in-band interference. This has the effect of raising the noise floor which
has the potential to mask the desired signal.
In wireless mesh networks, in-band interference is usually caused by the many nodes
operating within the mesh. Because the transmitted signals are very similar to each other,
it is highly likely that they will interfere with each other and affect the receivers’ ability to
receive the intended signal. The AvMeshTM Communications System mitigates this issue by
allowing the nodes to wait a predetermined amount of time before they transmit. As the
signal propagates down the runway, each node delays repeating the message by 0.6-3.2
seconds so that the nodes are not repeating over the top of one another and interfering
with one another.
3.6.2 In-band interference

16
3.7 Spectrum Analyzers
To comprehend the extent of potential sources of interference, an analysis of the actual
conditions at the intended receiver site is required. This analysis is usually done by a
Spectrum Analyzer which is an electronic measurement device that helps to determine the
type and frequencies of interfering signals. Unlike an oscilloscope which shows waveforms
in the time domain (with time and voltage on the x and y axes respectively), the spectrum
analyzer shows waves in the frequency domain (with frequency and amplitude on the x
and y axes respectively). By examining the amplitudes of signals at different frequencies
it is possible to measure the frequencies of these signals and deduce what signals are
present in the communications system.
Multiple types of Spectrum Analyzer are available and each type operates in a different
manner. A few examples of Spectrum Analyzer are briefly explained in the sections below.
3.7.1.1 Swept or Superheterodyne Spectrum Analyzer
This is the most traditional type of spectrum analyzer. The principle of the Swept
Superheterodyne Spectrum Analyzer is to convert the frequency of a signal to a lower
intermediate frequency by mixing it with another signal generated by a local oscillator.
The spectrum analyzer sweeps across the frequency range of interest, displaying all the
frequency components present while varying the frequency of the local oscillator linearly
across the frequency band.
The signal (with frequency f1) that is picked up by the transmitting antenna passes through
an attenuator and low pass filter and then enters a mixer where it is mixed with another
signal (f2) generated by the local oscillator. This results in the creation of 2 new signals, one
at the sum frequency (f1+f2) and the other at the difference frequency (f1-f2) as well as the
original signals f1 and f2. The signals then pass through an Intermediate Frequency filter
where the signal with the difference frequency (f1-f2), also known as the IF signal, is able to
pass through. The converted signals that fall outside the passband of the filter are rejected.
The IF signal is then converted to a signal voltage that can be passed to the display.
3.7.1.2 Fast Fourier Transform Spectrum Analyzer (FFT)
The FFT Spectrum Analyzer samples an input signal in the time domain and uses the
Fast Fourier Transform to convert it to the frequency domain and displays the resulting
spectrum.
The first stage of the FFT Spectrum Analyzer ensures that the received signal is at the
correct level for the conversion from the time to frequency domain through the use of
either a variable gain amplifier or attenuator. The signal is then passed through a low-
pass filter where any frequency elements that are higher than the frequency range
of the spectrum analyzer are removed. The sampler circuit then takes samples of the
signal at discrete time intervals and the samples are then passed to the analog-to-digital
converter (ADC) which converts the samples to digital form. The FFT analyzer receives the
digital samples (still in the time domain) into the frequency domain using the Fast Fourier
Transform which are then passed to the display.
3.7.1 Types of Spectrum Analyzer

AvMesh® RF Communications Systems
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Latest products and information available at www.avlite.com 17
3.7.1.3 Real time Spectrum Analyzer
The Real Time Spectrum Analyzer is a variation of the FFT Spectrum Analyzer.
However, unlike the FFT Spectrum Analyzer, the real time spectrum analyzer has a very
fast digital signal processor that is capable of capturing and analyzing all of the signals
within a particular bandwidth very quickly, virtually in real time. As a result, the Real
time spectrum analyzer is also able to capture signals that have an intermittent nature
(transients) that would otherwise be difficult to capture using other spectrum analyzers.
3.7.1.4 USB Spectrum Analyzer
USB Spectrum Analyzers use the computer to which they are connected to carry out the
data processing, thereby saving a significant amount of the cost associated with a more
traditional bench top instrument. Real time analysis is not possible as the computer system
that the USB spectrum analyzer is connected to usually runs on a PC Application not
capable of real time operation.
An understanding of Decibels is essential to be able to comprehend signal measurements.
The Bel is used as a way of comparing signal strength, however, its large values make it
difficult to use for precise measurements and calculations. The decibel (dB) is a smaller
unit as it is one tenth of a Bel and therefore provides more precise measurements and
calculations. The decibel (dB) is a ratio used for comparing two values and is used primarily
as a comparison of power level (although the ratio is applicable for other values such as
voltage and intensity as well). By using a logarithmic scale, the decibel is able to compare
quantities that may have a significant difference between them.
The comparison of power levels is computed using the following formula:
Where the log function is of base 10, ‘X’ is the number of decibels, ‘Pout’ is the output power
level and ‘Pin’ is the input power level, also known as the reference power level. The value
of Pout/Pin is known as the ‘Power ratio’. The factor ‘10’ has been included in the formula to
accommodate for the conversion from Bels to Decibels (there are 10 Decibels in one Bel).
If the output power is larger than the input power, the power ratio is more than 1 and the
resultant decibel value (X) becomes positive. This is known as a ‘gain’ or ‘amplification’
which results in an increase of power (signal strength).
If the output power is less than the input power, the power ratio is less than 1 and the
resultant decibel value (X) becomes negative. This is known as a ‘loss’ or ‘attenuation’ and
results in a loss of power (signal strength). A loss (Attenuation) is therefore expressed as a
negative gain.
The table below shows how the decibel value can be used as a comparison between the
output and input power values. For example, a decibel value of 3dB (gain) indicates that the
output power is twice the input power whereas a decibel value of -3dB (loss) indicates that
the output power is half the input power. Because of the logarithmic scale, even a small
change in dB value has a significant impact on the actual power (signal strength).
3.7.2 The Decibel formula

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Decibel formula
X dB [10log (Pout/Pin)] Power ratio (Pout/Pin)
60 1 000 000
50 100 000
40 10 000
30 1 000
20 100
10 10
3 2
0 1
-3 0.5
-10 0.1
-20 0.01
-30 0.001
-40 0.0001
-50 0.00001
-60 0.000001
The notation of the Decibel typically follows the form dBx, where ‘x’ is the reference unit.
Common dBx terms are shown below:
• Decibels relative to 1 milliwatt (dBm)
• Decibels relative to 1 Watt (dBW)
• Decibels relative to 1 microvolt (dBµV)
• dBi and dBd
dBi is the gain of an antenna relative to an isotropic antenna.
dBd is the gain of an antenna relative to a dipole antenna.
These are related by dBi=dBd + 2.15

AvMesh® RF Communications Systems
Installation & Service Manual
Latest products and information available at www.avlite.com 19
3.7.3 Signal to Noise Ratio (SNR or S/N)
The signal to noise ratio is defined as the ratio of signal power at the receiver to the noise
floor and is often expressed in decibels. The lower the noise generated by the receiver or
the higher the signal strength, the higher/better the signal to noise ratio is. This translates
to a clearer signal transmission
In decibels, the Signal to noise ratio is given by the following formula:
Where VSis the strength of the desired signal and VNis the strength of the noisy signal,
both in units of voltage (i.e. Volts, millivolts, microvolts etc.) These measured values are
obtained from the Spectrum Analyzer as it shows the signals on a graphic display.
If the strength of the desired signal is equal to the strength of the noisy signal, the signal to
noise ratio will be zero. As a result, the desired signal will border on being unreadable since
the noise level severely competes with it.
Ideally, VSshould be larger than VNso that the signal to noise ratio is positive. This will result
in the desired signal being readable. Therefore, as long as the desired signal is well above
the noise floor, then the transmission will be of a higher quality.
In situations where VSis smaller than VN, the signal to noise ratio is negative and reliable
communication is generally not possible unless the noise level is decreased and/or the
strength of the desired signal is increased.

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4.0 AvMeshTM Communications System:
Theory of Operation
The AvMeshTM Communications System operates by broadcasting signals to the lights
in the system via a mesh network which is made up of a primary network and reserve
network. The primary AvMeshTM network serves as the main pathway for signal
propagation through the system. The secondary network provides a backup path for the
signals if the primary network fails.
In the AvMeshTM Communications System, signals are sent from the Avlite wireless
remote controller to the lights that are within range (approximately 1.4km but this may
decrease depending on a number of factors). From here, the signal is resent by the nodes
to the other lights within range (approximately 300m but this may decrease depending
on a number of factors) until the signal has been sent to all of the lights throughout the
entire mesh network. It is important to note that the signals mostly rely on line-of-sight
propagation in order to be transmitted and received by the lights. If the lights are not in
direct line of sight to each other, they will not be able to pass on the signals.
As the message propagates through the area such as a runway, each node delays
repeating the signal by 0.6-3.2 seconds. This is done so that the nodes are not repeating
over the top of the controller or each other. It is important to note that for distances greater
than the operational range of the lights, there may be a delay in those lights receiving the
information, as the further away the lights are from the controller, the longer it will take the
signal to propagate to all lights in the system.
The airfield lights are typically clustered into ‘Light groups’ which allow the lights in an area
such as a taxiway to be controlled in unison. As a result, different light characteristics such
as ON/OFF functions, light intensities or operational modules (e.g. visual or infrared) can be
controlled all at once. The airfield lights can be configured for up to 10 different light groups
such as taxiways, runway edge or threshold and each light group is able to be controlled
independently.
Each light in the AvMeshTM Communications System is capable of determining whether or
not it needs to become a node and repeat commands in the mesh network. The lights are
able to configure themselves as either primary or reserve nodes or remain as listen only
lights depending on what is required to provide the airfield enough coverage.
• Primary Node
The primary nodes make up the primary network. This node is able to receive and decode
signals from the Avlite wireless remote controller, another primary node or a reserve node
and act upon the signal itself. The primary node is able to pass on the received signal to
other lights within range.
4.1 Node Information