RF System Design Program
Instructions
Wireless communication is being used in all facets of industrial applications from
voice to data, but few people have a working knowledge of radio or how to design a
Eric P. Marske
Customer Support
reliable communication system. Every radio frequency (RF) application is unique.
ESTeem Wireless Modems
Although many radio applications are similar or provide the same coverage area, no
two are exactly the same. Understanding that each radio system is different explains
why each site needs to be tested. Wireless vendors provide a dizzying array of ranges and specifications for their
products and this paper will help you sort through this information and terminology.
The purpose of the paper is to introduce some basic radio concepts and how they apply them to designing a reliable
communication system. Radio system design is not a difficult process but it does take some time prior to selecting
the final hardware for the application. Your time is well spent because it can point out problems in the selected
hardware and allow radio system design modifications prior to installation and eliminate costly rework.
Radio site analysis can be broken down into three phases; first is the initial site work, second is the RF data
analysis and the final phase would be the on-site testing. This paper and presentation will focus on the first two
phases of this process because the final on-site testing phase is a validation of the calculated values in the first two
phases. This on-site radio survey requires RF test equipment that few people outside the radio world will have.
The tool used by RF system designers in the site analysis phase is a computer software program that calculates all
radio parameters and allows the user to evaluate how the radio equipment will operate in the supplied conditions.
There are many computer programs on the market ranging to thousands of dollars, but the one we are going to use
as an example in this paper is proved by ESTeem Wireless Modems.
Radio Basics
Radio Frequencies
In the United States use of frequencies in the electromagnetic spectrum, known as the radio spectrum, for wireless
communication is governed the Federal Communications Commission (FCC). Frequencies in this radio spectrum
are divided up for use by application such as radio and television broadcasting, navigation and wireless
communication to name just a few. There are specific frequencies used for two-way voice and digital telemetry
applications within this radio spectrum that provide a majority of the wireless applications in use today.
Licensed and Unlicensed Frequencies
Within the radio frequency band, the FCC has designated specific frequencies as Licensed and Unlicensed. Use of
a radio transmitter in a licensed frequency band requires that each site’s location, output power and bandwidth be
filed with the FCC for use in coordinating transmitting stations. These licensed frequencies use a single, narrowband, channel to transmit all their data. The licensing process allows multiple users in an area to operate on
separate frequencies and not cause undue interference with each other.
The unlicensed frequency bands are open for all users in an area that have the equipment itself certified by the FCC
to fit within specific transmission guidelines. These guidelines allow radios in an area “an even playing field”
where the hardware itself is used to differentiate between other transmitters. The most common method for this
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type of transmitter is known as spread-spectrum. The designated widths of the radio frequency channels
(bandwiths) are much greater in the unlicensed frequency bands than those in the licensed frequencies and the radio
hardware can provide a much higher data rate.
Radio Frequency Selection
The first step in designing a wireless application is determining the correct frequency band for use. There are
frequencies available for use in both the licensed and unlicensed frequency band (Table 1). In general, the
application itself will dictate what frequency band to use. For example, if you are looking to installing a highspeed wireless Ethernet system you will be using either the 2.4 GHz or 5 GHz frequency bands.
Licensed Narrow Band Radios
Frequency
Tx Power
RF Data Rate
Interfaces
72 to 79 MHz
1 Watt
1.2 to 19.2 Kbps
RS-232/422/485
150 to 174 MHz
1 to 40 Watts
1.2 to 19.2 Kbps
RS-232/422/485
400 to 420 MHz
1 to 40 Watts
1.2 to 19.2 Kbps
RS-232/422/485
450 to 470 MHz
1 to 40 Watts
1.2 to 19.2 Kbps
RS-232/422/485
900 Mhz
2 to 4 Watts
1.2 to 19.2 Kbps
RS-232/422/485
Spread Spectrum, Unlicensed Radios
Frequency
Tx Power
RF Data Rate
Interfaces
900 Mhz
.1 to 1 Watt
100 to 150 Kbps
RS-232/422/485
2.4 GHz
.1 to 1 Watt
100 to 171 Kbps
RS-232/422/485
Ethernet, Spread Spectrum, Unlicensed Radios
Frequency
Tx Power
RF Data Rate
900 MHz
.1 to 1 Watt
.1 to 500 Mbps
Interfaces
Ethernet
2.4 GHz
.1 to 1 Watt
.1 to 11 Mbps
Ethernet
5 GHz
.1 to 1 Watt
.1 to 54 Mbps
Ethernet
Table 1 – Radio Types
Decibels
The decibel (dB) is a unit of measure used in all mathematical calculations in the radio world. The decibel is a
logarithmic number (10 log (linear number)) used when calculating the power factors to the gains and losses in a
radio system. All radio components such as antennas, coax cables, receiver sensitivities and transmitter powers are
rated on this common unit of measure. Since you can multiply and divide linear numbers by adding and
subtracting their logarithms, this can greatly simplify the mathematics. An easy rule to remember when dealing
with decibels is that a three decibel increase (+3dB) will double your output power, while a three decibel decrease
(-3dB) will cut your power in half.
Feedlines
Most radio applications require that the antenna be mounted in a different location than the radio transceiver. The
devices used to feed the energy from the transmitter to the antenna is a special type of cable called a coaxial cable
or better know as coax. The coax cable is a tuned pipeline that allows movement of the energy produce by the
transmitter to the antenna with a minimal amount of signal loss. Different cable types have different losses and
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those losses are based upon their length. Table 2 lists some common coaxial cable types used in radio applications.
All coax cables have signal loss regardless of the diameter or cost. You can see that the higher the frequency the
greater the signal losses and how the length of the cable greatly effects how much signal will arrive at the antenna.
Frequency Band (MHz) 66 to 79
150 to 174
400 to 420
450 to 470
900 to 940
2400 to 2500
5100 to 5400
RG-58
2.5
5.2
8.4
9
13.7
n/a
n/a
LMR195
2
4.4
7.8
7.8
11.1
19
38
RG-8 (Solid)
1.1
1.7
2.9
3
4.5
7
14
LMR600
0.547
0.964
1.72
1.72
2.5
4.42
7.3
3/8" Heliax
0.084
1.48
2.48
2.64
3.97
6.47
10.2
1/2" Heliax
0.463
0.88
1.36
1.45
2.17
3.52
5.5
7/8" Heliax
0.254
0.486
0.758
0.808
1.23
2.02
3.4
Table 2 – Feedline Losses
Antennas
An antenna is a tuned element that allows the energy from the transmitter to radiate into open air. The length of an
antenna is based upon the wavelength of the tuned frequency. There are many different types of antennas but they
can be put into two general categories; omni-directional antennas and directional antennas. Omni-directional
antennas radiate energy in all directions from the antenna (Figure 1). These antennas are used in locations that
communicate to more than one remote site such as the Master or Repeater nodes.
360 degrees
Top View
Radiation Pattern
Vertical Polarization
Side View
Radiation Pattern
Vertical Polarization
Omni-directional Antenna
Vertical Polarized
Figure 1 – Omni Directional Antennas
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A directional antenna radiates a majority of the transmitter energy in a single direction. This radiation pattern will
have an area on both the vertical (up and down) and horizontal (side to side) plane where most of the energy is
being focused (Figure 2). The angle that this pattern creates is known as the vertical and horizontal beamwidth.
These angles are used when installing the antenna to verify that the energy will be directed to the correct site.
These antennas are best suited for use at remote sites in multi-point system or point-to-point applications.
3 dB Points
3 dB Points
Vertical Beam
Width
(degrees)
Horizontal
Beam Width
(degrees)
Back Lobe
Back Lobe
Top View
Radiation Pattern
Vertically Polarized
Side View
Radiation Pattern
Vertically Polarized
Figure 2 – Directional Antenna Patterns
An antenna is a passive device and can not increase the amount of power from a transmitter, but as we see in the
directional antenna, the total amount of radiated energy can be manipulated in a specific direction. This
manipulation of the radiation pattern can increase or decrease the amount of received signal in a given area.
Antennas will have a gain (+dB) or loss (-dB) based upon their design and how efficient they radiate energy. The
higher the gain of the antenna, the more directional it becomes. The gains or losses on the antenna also increase or
decrease the received signal strength by the same power factor.
Another phenomenon that needs be addresses when using antennas is their polarization. The horizontal or vertical
polarization of the radiating element is based upon its reference to the Earth surface. All antennas in a radio system
need to be on the same polarization or losses will be induced. Most wireless industrial telemetry applications or
Supervisory Control and Data Acquisition (SCADA) systems combine both omni-directional and directional
antennas. Vertical polarization is the only type that is generally be used in a combined antenna system.
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Effective Radiated Power (ERP)
We have now seen that the major components in a radio system (the transmitter, coax cable and antenna) all effect
each other through gains and losses. The end result is the total energy radiated from any radio site or the Effective
Radiated Power (ERP). The ERP is calculated by taking the transmit power of the radio, subtracting the losses in
the coax cable and adding the gain of the antenna.
TX Power-Feedline Loss +Antenna Gains = ERP
This simple calculation is the basis for all further RF site calculations.
Line of Site (LOS)
The term Line of Site is used by all radio manufactures, but what does it mean and why is it of such concern? All
frequencies used for industrial wireless communication (Table 1) require a clear, unobstructed path between
antennas to make any predictions on system performance. If anything such as trees, buildings or hills are in the
direct radio path between the antennas the RF energy will be reflected, absorbed or scattered and signal loss will
occur. The amount of these losses will be based on frequency and the composition of the reflecting material. In all
cases, if there is no LOS between the antennas, predictions on system performance can not be accurately made and
on-site testing is required.
If evaluating a radio system’s performance over a distance of miles, the curvature of the Earth’s surface and its
effect on required antenna heights must also be evaluated. As we have learned, line of site is critical to making
predictions on system performance. As the distance between two radio sites increases the minimum height to clear
the Radio Horizon will also increase (Figure 3). To maintain a clear line of site, adjustments may needed to the
antenna height on either end of the system.
Distance (miles)
Minimum
Height (ft.)
Radio Horizon
Earth
Minimum
Height (ft.)
Antenna B
Antenna A
Figure 3 – Minimum Antenna Height Required to Clear Radio Horizon
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Freznel Zone
With the use of higher frequency transmitters (2.4 Ghz and above) in high-speed wireless networks, another radio
phenomenon called the Freznel zone must be considered. Radio waves to not radiate out in straight lines. The
Fresnel zone is the ellipsoid spread of the radio waves around the visual line-of-sight after they leave the antenna
(Figure 4). This area must be clear of obstructions or the signal strength will be reduced due to signal blockage.
Typically, a blockage in the first 20% of the Fresnel Zone height introduces little signal loss to the link. Beyond
40% blockage, signal loss will become significant. The height of the Freznel zone will be calculated and displayed
in the RF Design Tools when using frequency bands that are more effected by these blockages.
Fresnel Zone
D (miles)
R (ft.)
Figure 4 – Freznel Zone Diagram
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Fade Margin
The minimum amount of signal that a receiver requires to correctly demodulate the data is called the receiver
sensitivity. The fade margin is the amount of signal, in dB, above this receiver sensitivity. All hardware gains and
losses (transmitter power, coax cable, antenna, spreading losses) on both ends of the radio system (Figure 5)
control the fade margin.
Effective Radiated Power
Spreading Losses
(Controlled by Nature)
Tx Antenna Gain
Rx Antenna Gain
Feedline Losses
Feedline Losses
Tx Power
(watts)
Rx Sensitivity
(dBm)
Lightning
Arrestor
Lightning
Arrestor
Figure 5 – Total Fade Margin Diagram
The fade margin is the most critical piece of information in radio system calculations. The radio system reliability,
efficiency and data rate are directly related to the fade margin. The reason we need fade margin is because the
radio world is not perfect. Equipment ages, antennas go out of alignment or unexpected naturally occurring or
man-made noise interferes with the radio signal. With a fade margin designed in the system, the radio can continue
to operation through these conditions. Without a fade margin the system will fail over time.
The minimum fade margin for any radio system is 3dB above the total background noise on a frequency, better
know as the noise floor. The amount of fade margin can also predict the expected link retries over time.
•
•
•
10dB = 10% Link Retries
20dB = 1% Link Retries
30dB = 0.1% Link Retries
As you can see, the greater the amount of fade margin designed in the radio network from the beginning will
provide a more reliable link in the future.
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Initial Site Work
Pump Site #3
5.
S
LO
s
ile
m
5
LOS
N
LOS
Water Tank
ile s
9m
3 miles
Pump Site #2
LO
Pump Site #1
LOS
S
5m
es
6 mil
ile s
LO S
Control Room
Figure 6 – Example Site Layout Diagram
Now that we have a good understanding of the terms used in radio system design, it is time to begin our analysis.
Before we begin to use the Site Design software, we need to gather some information on the radio site.
1. Simple Site Layout - All radio systems are a series of point to point links and each of these links will need
to be evaluated. Begin by making a simple diagram of all locations in the radio system. Include all
locations where the radio communication is required (Figure 6).
2. LOS - Mark all areas on the diagram where there is no line of site (LOS) between the antennas (Figure 6).
3. Distances - Mark all distances between sites on the diagram that have a line of site or will need communication
between them. Distances can be gathered from site maps, GPS data or if the longitude and latitude for each site
is known, the Site Design software has a tool for calculating the distance between two points given the
longitude and latitude of each point.
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4. Site Data Chart – Make a site data chart like the one in Table 3.
Site Information
Name
Site Elev. Elev. Dif. Ant. Hgt. Adj. Ant. Hgt. Feedline Lgh.
Control Room
560
80
20
100
30
Pump Site #1
570
90
20
110
30
Pump Site #2
820
340
20
360
30
Water Tank
1100
620
120
740
130
Pump Site #3
480
0
15
15
30
Ant. Type
Omni-Dir.
Direction
Direction
Omni-Dir.
Directional
Table 3 – Site Data Chart
5. Elevation – Find the elevation above sea level for each node in the system and put the values in the Data Chart.
Site elevation can be gathered from a topographical map or GPS data.
6. Antenna Height – Estimate the antenna height (in feet) above ground level (Figure 7) required to achieve LOS
to the designation site and mark the values in the Data Chart.
7. Cable Length – Estimate the feedline length (in feet) from the antenna to the equipment cabinet (Figure 7) and
mark the length in the Data Chart.
8. Elevation Differential – The elevation differential is used to relate all antenna heights to each other in single
system. To calculate the elevation differential for all sites in the system, find the site with the lowest elevation
and make its value 0 in the Data Chart. Subtract the elevation of this lowest site for all other elevations in the
system and mark their values in the Elevation Differential block.
Adjusted Antenna Height – To calculate the adjusted antenna height, add the value from the Antenna Height
block to the Elevation Differential block.
Site Information
Name
Site Elev. Elev. Dif. Ant. Hgt. Adj. Ant. Hgt. Feedline Lgh.
Control Room
560
80
20
100
30
Pump Site #1
570
90
20
110
30
Pump Site #2
820
340
20
360
30
Water Tank
1100
620
120
740
130
Pump Site #3
480
0
15
15
30
5.5
S
LO
Ant. Type
Omni-Dir.
Direction
Direction
Omni-Dir.
Directional
Pump Site #3
les
mi
LOS
N
LOS
Water Tank
9m
ile s
3 miles
Pump Site #2
LO
Pump Site #1
LOS
S
5m
ile s
es
6 mil
LOS
Control Room
Figure 8 – System Layout and Data
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9.
All the data you will need for using the RF Design Program is now available in the Site Data Chart and the Simple
Site Layout Figure 8.
Antenna
Feedline
Height of Antenna
Above Ground
Equipment
Cabinet
Terrain Height Above
Sea Level
Figure 7 – Estimated Antenna Height and Cable Length
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Rf Site Design Program
The ESTeem RF Site Design Tool is a Microsoft Excel® spread sheet that analyzes all the data we have gathered
on the site during the Initial Site Work. The program automatically calculates the system gains, losses and heights
and displays these values on the screen (Figure 9). Through comparisons from on-site measurements to calculated
values, the calculated values tend to be more conservative.
Figure 9- RF Design Tools Screen
You will want to analyze all communication paths in the system, such as the Master to Remote, Master to Repeater
or Repeater to Remote. Each of these point to point link tests will build the backbone for the entire RF system. As
an example, we will use the radio site in (Figure 6) and select a radio that will provide us a high-speed wireless
Ethernet system. Any radio vendor hardware can be tested with the software but for this example we will use the
ESTeem Model 192E, 2.4 GHz Wireless Ethernet modem.
All communication paths in a radio system need to be evaluated. We will be looking at a few select paths in our
example site that provide some unique conditions and discuss how to deal with them.
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Site Example 1 – Control Room to Pump Site #1
We will begin our analysis by looking at the link from the Control Room to the Pump Site #1 (Figure 10). Using
the information we gathered during the initial site work, enter all information into the Data Entry Keyboard
section of the program (Figure 10).
Pump Site #3
5 .5
S
LO
le
mi
s
LOS
N
LOS
Water Tank
ile s
9m
3 miles
Pump Site #2
LO
S
LOS
5m
iles
Pump Site #1
es
6 mil
Control Room
Site Information
Name
Site Elev. Elev. Dif. Ant. Hgt. Adj. Ant. Hgt. Feedline Lgh.
Control Room
560
80
20
100
30
Pump Site #1
570
90
20
110
30
Pump Site #2
820
340
20
360
30
Water Tank
1100
620
120
740
130
Pump Site #3
480
0
20
20
30
Ant. Type
Omni-Dir.
Direction
Direction
Omni-Dir.
Directional
Figure 10 – Control Room to Pump #1 Data Entry
Once all the site data has been entered the RF Path Analysis will be displayed (Figure 11). Note that all the
calculated radio site values such as ERP, Feedline Loss, TX Power, Expected RX Signal Strength, Receiver
Sensitivity, and Maximum Distance are displayed for each end of the radio system. The key site data such as Fade
Margin, Height Warnings and Freznel Zone Warnings will be displayed in the center of the data field and will turn
red if a problem is found in the link.
The Fade Margin for this radio path is calculated at 6.5dB for the equipment we specified. This number will
increase or decrease with any hardware change in the system. Remembering that the fade margin level we are
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Figure 11 – Example 1 - RF Path Analysis
looking for during analysis is greater than 3dB, this communication link will work reliably at 11Mbps over the
distance of 6 miles.
Site Example 2 – Pump Site #2 to Water Tank
If we look at the link from the Pump Site #2 to the Water Tank (Figure 12) we will see that distance is 9 miles.
Using the information we gathered during the initial site work, enter all information into the Data Entry Keyboard
section of the program.
Pump Site #3
5 .5
S
LO
mi
le s
LOS
N
LOS
Water Tank
iles
9m
3 miles
Pump Site #2
Pump Site #1
LOS
LOS
es
6 mil
5m
iles
LOS
Control Room
Figure 12 – Example Site #2 Layout Diagram
The results from the RF Site Analysis data show that this link is not operational (Figure 13). There are a few
changes that we could make to the system to make it function. Increasing the gain on the antenna would raise the
fade margin, but still leave the link marginal (<3dB). If we lower the data rate on the ESTeem to 1Mbps (-91dBm
Receiver Sensitivity) the fade margin will increase to 6.5dB. We already have a communication link directly from
the Control Room to Pump Site #2 so we will let that be the primary communication pathway.
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Site Example 3 – Water Tank to Pump Site #3
For our final example, we will look at the link from the Water Tank to the Pump Site #3 (Figure 14). Using the
information we gathered during the initial site work, enter all information into the Data Entry Keyboard section of
the program.
The results from the RF Site Analysis data show that this link is operational but there is a problem in the selected
antenna height (Figure 15). The remote site height of 15 feet is below the minimum Freznel zone height of 19.5
feet. By increasing the height of Pump Site #3 to greater 19.5 feet height of the Freznel Zone) a serious problem in
signal strength can be avoided.
Pump Site #3
N
5.
s
ile
5m
LOS
LOS
Water Tank
LO S
ile s
9m
3 miles
Pump Site #2
Pump Site #1
LOS
LOS
es
6 mil
5m
iles
LO S
Control Room
Figure 14 – Example Site 3 Layout Diagram
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Figure 13 – Example 2 - RF Path Analysis
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Figure 15 – Example #3 - RF Path Analysis
Lessons Learned from Using RF Design Tools
•
•
•
By using the RF Design Tools, prior to installation, we have identified radio sites where the RF signal level is
too low for reliable communications and sites were the antenna height was too low.
With small adjustments to the radio system design, we could easily correct any of these found problems and
would have dramatic effect on system performance. These adjustments can be made by simple hardware or
location changes saving many hours and costs if the site were already installed.
A quick site evaluation has pointed out several radio problems that could not be identified on a map and could
not be predicted based upon the rated communication distance of the product.
Conclusion
Radio system design is not a difficult process, but the time spent planing and evaluating the radio hardware are key
to a reliable communication network. With education and the proper tools you can be confident in the system you
design. Use the knowledge and tools learned in this paper to evaluate the claims from different radio
manufacturers and make an informed decision on the radio hardware you will use for your next application. We
want you next wireless application to be a success and we hope that the information provided will give you the
confidence to design your own radio system.
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