Correct Antenna & Survey Report
ANTENNA TYPES
Sigsense has three different antennas to match conditions on site:
1dBi Omnidirectional Antenna
This antenna is a cost-effective solution but should only be used where signal strength is excellent (refer to Signal Strength Table).
It is a low-gain antenna with a short cable that can be mounted close to the Captis.
6.5 dBi Omnidirectional Antenna
This is the general-purpose antenna for Captis LID deployments. It's suited for a variety of applications and typically used where signal strength is excellent through to poor.
It has a 5m cable that allows the antenna to be mounted high enough to clear most obstructions. The bottom of the antenna is threaded and supplied with a mounting nut to allow for easy on-site installation.
11dBi Directional Yagi Antenna
This antenna is used for installations where signal is fair to poor or where the signal is required to be transmitted long distances.
Directional antennas have a higher transmission power at the cost of narrower beam angle and as a result, they need to be aimed accurately at an applicable tower. Directional antenna are also more susceptible to interference due to line of sight blockages.
SIGSENSE CAN ASSIST WITH OPTIMAL POSITIONING/DEPLOYMENT OF THESE ANTENNA
UNDERSTANDING A SITE SURVEY REPORT
Following are some of the important factors found in a site survey report with further context to provide understanding.
Bearing
Bearing indicates a direction in degrees the intended receiving tower is relative to the installation.
Mounting Height
This height (in metres) defines how high the antenna is mounted. Mounting the antenna higher will often allow a better signal as there is less chance of obstruction between transmitting and receiving devices.
Line of Sight
In radio communications, line of sight (LOS) is defined by the straight path between a transmitting device and the receiving device.
In point to point wireless communications, it is important for the LOS between two devices to be free from any obstruction (hills/mountains, trees, buildings etc.). Interference or obstruction in the LOS can result in a loss of signal.
Fresnel Interference
Radio signals do not propagate in a straight line. Surrounding the LOS / transmission pathway between the transmit antenna and the receive antenna is an elliptical region called the Fresnel Zone. This zone defines the potential path the signal can travel between the 2 points. The size of the ellipse is determined by the frequency of operation and the distance between the two sites.
Aim Back
How well the tower faces the chosen location. The lower the value, the better the tower faces your location. A value of 0 degrees means the directional antenna is pointing directly at the location. This is the ideal situation. Signal strength diminishes until the aim back is approximately 30 degrees where a typical loss of 3dBi is common. At 60 degrees and over, the signal will weaken even further.
A useful analogy to use is directional antennas are like a flashlight. Point it at your face, and the light is very bright; that's 0 degrees aim back. Aim the flashlight 30 degrees to one side of your face and the light becomes much less intense but you still see the light. A directional antenna works the same way, except it's transmitting at a much lower frequency invisible to the eye.
Path Loss
Path Loss is the estimated signal loss as the signal travels through the air between the transmission and receiving devices. Lower path loss is better (e.g. 90 is better than 110 and much better than 130). Path loss considers transmit frequency, distance, and approximate antenna losses in its calculation but does not consider losses due to Fresnel zone interference.
Signal Loss
Loss refers to signal losses incurred when the signal travels from the device to the antenna at the cell site. Typically, it's related to cable length. If the device is near the antenna, the loss will be much smaller than if the device is on the ground in a shed.
SITE SURVEY REPORT EXAMPLE
A - Proposed LID Location
This is the proposed LID location
B - The Telstra Tower
The space between A & B shows the elevation changes. Green indicates land and blue will indicate water.
C - The Fresnal Zone
The oval connecting A - B represents the Fresnel zone and the line in its centre is the line-of-sight. Red bars show where the terrain intersects the Fresnel Zone, affecting signal strength. A Fresnel zone with no interference delivers optimal signal reception.
D - Location Information
Antenna height above ground (5m)
Horizontal aim back measures how far A is from the centre of the directional antenna at B. Lower numbers indicate higher signal strength.
Path loss calculation (103.1 dB) estimate the strength of signal received at A transmitted from B. A smaller number means a stronger signal (eg. 90 is better than 130). Calculation considers transmit frequency, distance, and approximate antenna losses. Calculation does not consider losses due to Fresnel zone interference.
E - Antenna Information
Antenna height above ground (76m)
Transmit frequency (778.0 MHz)
Receive frequency (723.0 MHz)
Horizonal azimuth : Antenna horizontal direction. 0° is north, 90° is east, etc.
Vertical Elevation (0°): Antenna vertical direction. 0° is at horizon, 3° is downwards
Antenna gain (10.2 dBi): Its effects are captured in path loss calculations
Line loss (2.3 dB): Signal loss as it travels from radio to antenna
Radio power (51.0 dBm): Output power from radio (dBm = decibel milliwatts)
Transmit bandwidth (20MHz): 5 MHz is sufficient for IoT; 40 MHz is excellent for wireless broadband
Service type:
a. Macrocell = traditional cell tower, building, water tower, etc. A very tall tower can transmit 10 or more kilometers
b. Metrocell is a short < 8m tall site; services neighborhood (usually < 1 km^2)
c. DAS is an in-building site that transmits only within the building or stadium