RF planning 101

This guide serves as a generic tutorial on RF planning, targeted at beginners and novice equipment users. It will arm you with enough knowledge to use the majority of the features in the various CloudRF interfaces but is by no means comprehensive. RF planning is an art which takes years to master.

Abbreviations

Knowing what things mean is half the battle.

Abbreviation Description
ERP Effective Radiated Power in watts. See Transmitter section
Tx Transmitter (Device which sends a signal)
Rx Receiver (Device which receives a signal)
GHz Gigahertz. Unit of measurement for frequency
MHz Megahertz. Unit of measurement for frequency
W Watts. Units of measurement for power
dB Decibel. See units section
dBm Decibel milliwatt. See units section
dBuV/m Decibel micro volts per metre. See units section
dBi Decibel isotropic. See antennas section

Units

dB, dBm, and dBuV/m are all different values for describing RF. dB is described as 'Path loss' and is agnostic to whatever RF power is used. For example, a 2.4GHz signal over 100m has a path loss of 80dB. You can calculate this quickly with a simple tool like this. dBm is described as 'received power' and is a ratio relative to 1 milliwatt. It is the default setting in CloudRF and factors in RF power expressed as a negative value between -1 and -110dBm. The RF noise floor is described in dBm and is generally near -120dBm. A good signal (eg. 5 bars on your mobile phone) is > -70dBm. An average signal is > -90dBm and a weak signal is

Transmitter

You can learn a lot about your transmitter from your device's documentation. As a minimum you need to know it's frequency and power output.

Frequency (MHz/GHz)

If the frequency isn't listed in your system's documentation: Google it.
Something like a PMR446 handheld radio may list the precise channels it operates on eg. 446.025MHz whereas another system may list a band eg. 2.4GHz because it occupies multiple channels dynamically. Where precise frequencies are not known you should apply the most accurate frequency you can (2437MHz is in the middle of the 2.4GHz band for example).

RF Power

The RF power can be expressed in both Watts and dBm and is easy to get wrong! Just because your system says it emits 1 Watt (30dBm) does not mean it does due to losses in the antenna and cabling. You should look for a conservative value when calculating the total effective radiated power (ERP). CloudRF has an automatic ERP calculator so when you enter in 1 Watt and an antenna gain of 9dBi you get 4.8W (36.8dBm) total ERP. Communications authorities restrict power output for different bands so if in doubt, check what your RF ERP really is. This is normally implemented by the equipment vendor so is hard to override without reverse engineering the hardware.

Frequency band RF limit Europe RF limit USA
2.4 GHz 100mW / 20dBm 1000mW / 30dBm
5.8 GHz 100mW / 20dBm 1000mW / 30dBm

A handy lookup table for dBm to Watts is here.

Antennas

Getting the right antenna is important but don't worry if you're not sure. A common antenna called a dipole exists which serves most basic purposes where the transmitter is radiating in all directions. A mobile phone, walkie talkie, boat and plane all have dipole antennas.
An antenna has directional properties in the horizonal (azimuth) and vertical (elevation) planes. A directional antenna (eg. a TV aerial) has a high gain for signals in a given direction, represented as dBi (decibel isotropic). With dBi, a value of 2.15 represents normal gain. This figure is taken from a half wave dipole. A high gain antenna would have a value between 3 and 40dBi.
An antenna's radiation pattern can be documented as polar plots of the horizontal and vertical planes. This is what you see in the CloudRF interfaces. Once you've got the right antenna, you should align it correctly (only if it's a directional antenna) using the direction and down-tilt parameters. Down tilt would be zero if your antenna was parallel to the ground or a positive value if it was pointed down slightly. Many high capacity antennas on tall masts have positive down-tilt angles because they are pointed down to serve the closest subscribers. If you wanted to point an antenna up to the top of a hill it would have a negative down-tilt eg. -5 degrees.

Receivers

Knowing your receiver capabilities is vital to get an accurate prediction.
The single most important thing to get right is the receiver sensitivity. This value, normally expressed in dBm will make a huge difference. A mobile phone for example has a receiver sensitivity of about -105dBm. A handheld VHF radio is less at around -90dBm. If you are not sure, set this to -80dBm. This will give you a conservative prediction, allowing for fluctuations in the quality of the link referred to as the fade margin. Setting it lower than -90dBm is not recommended if you are unsure.

Environment

The terrain makes a huge difference and thankfully is automatically factored in by the system for you. There are other variables you can control which will affect your coverage.

Terrain conductivity

Depending on where your link is, the ground will affect your potential. Dry ground conducts less well than wet ground. Pick the best match from the selection list.

Radio climate

For signals operating through freespace, the climate will also affect your potential. Pick the best match from the selection list.

Clutter

Buildings present a real challenge to RF planning. You can simulate buildings through either an average height value eg. 8m for houses or by importing your own KML layer with large buildings defined. Our legacy competitors emphasise the importance of having accurate clutter data but the accuracy benefit must be traded off against the significant time and cost of doing so. What sales people won't tell you is that perfection is not possible with RF planning - all predictions are estimates based upon limited inputs and are subject to multiple random inputs like the weather or motor traffic. Set an average clutter height of 6m for suburban areas or 2m for rural areas.

Output

Resolution

Resolution refers to how accurate the prediction is. Values are the number of pixels per degree of latitude so 1200 (default) equates to approximately 90m per pixel and 3600 equals 30m (High accuracy). A higher resolution will take longer to calculate but we've multi-threaded our engine now so you should only wait a few seconds for most calculations.

Colour schema

The colour scheme you choose is not just cosmetic. The colours represent actual signal values, depicted in a colour key. As well as pre-defined schemas, you can define your own within the 'Custom RGB' option. This allows you to define the signal threshold levels for each colour and is perfect if you want to see just simple 'good' or 'average' maps.