Table of ContentsHow many Ethernet radios can I have in one radio network?Does bandwidth decrease when Repeaters are used?How many Repeaters are allowed?Why is a network limited to 15 radios when a Repeater is used?What causes RF signal loss?What factors should I consider when choosing antennas and cables?What guidelines should I follow when installing the antenna?What about antenna placement?When is the best time to complete a Radio Site Survey?What do the Signal and Noise numbers mean?
How many Ethernet radios can I have in one radio network?
A radio network is a group of radios communicating through a single Gateway radio. For BaseStation 1000 and BaseStation 3200 controllers, a radio network with no Repeaters can include one Gateway radio and up to 34 Endpoint radios, for a total of 35 radios. If a Repeater is required in the network topology, the maximum number of radios is 15, including Repeaters. If a site requires more radios than described above, additional Gateways can be used.
Does bandwidth decrease when Repeaters are used?
By design, when a radio network topology is configured to include a Repeater, the Gateway will communicate at a lower bandwidth in order to ensure reliable communications through the Repeater.
How many Repeaters are allowed?
Only one Repeater is allowed between a Gateway and an Endpoint. A radio network may employ multiple Repeaters as long as the total number of radios is kept to a maximum of 15 and no Endpoint radio path includes more than one Repeater.
Why is a network limited to 15 radios when a Repeater is used?
Adding a Repeater to a radio network means that a packet must travel through two radio paths instead of one, essentially doubling the amount of work the Gateway radio must do in the same period of time. Because it’s doing twice as much per packet, the network can only handle half as many radios.
What causes RF signal loss?
Several factors can contribute to RF signal loss. In a landscape application, the most common causes include (but are not limited to):
Free space loss: Free space loss is simply the reduction in signal that naturally occurs as the signal spreads out further away from the source.
Diffraction: Diffraction losses occur when an object is located in the line-of-sight path. Signals may be able to diffract around the object, but the diffraction will weaken the signal.
Terrain: Terrain changes, such as elevation changes, can significantly attenuate, if not completely obstruct, an RF signal.
Buildings and vegetation: Buildings not only reflect radio signals, but they can also absorb them. Vegetation such as a large tree can significantly weaken an RF signal, especially when the foliage is wet.
What factors should I consider when choosing antennas and cables?
Antennas add signal strength, but cables and connections create loss. In a landscape application, you should always use, at a minimum, an LMR400 low loss type cable. Generally, an LMR400 low loss cable will cause 1 dB loss per 25 feet. Each connection will result in approximately 0.1 dB loss per connection. Lightning arrestors, which are always recommended, will create approximately .2 to .25 dB signal loss.
When selecting antennas and cables, you should be sure that signal losses do not exceed the gain of the antenna. For example:
6 dB gain antenna (+6 dB)
50 ft. LMR400 cable (-2 dB)
3 connections (-0.3 dB)
Lightning arrestor (-0.25 dB)
6 dB – 2 dB – 0.3 dB – 0.25 dB = 3.45 dB gain
3 dB gain antenna (+3 dB)
100 ft. LMR400 cable (-4 dB)
3 connections (-0.3 dB)
Lightning arrestor (-0.25 dB)
3 dB – 4 dB – 0.3 dB – 0.25 dB = -1.55 dB Loss
What guidelines should I follow when installing the antenna?
All antenna cable connections should be weatherproofed. Connections left exposed to the elements will fail over time and prevent the radio from communicating.
Antenna cable connections can fail if strained. Strain relief should be provided for all cable connections wherever possible.
Follow all instructions provided by the manufacturer of the antennas, cables, and lightning arrestors you select.
What about antenna placement?
The goal is line of site. If you can’t see you it, the radio probably can’t talk to it.
Higher is usually better (but too high is also bad). You should install the antenna high enough to allow for clear line of site. Antennas placed too close to the ground cause unnecessary reflection and loss of signal. An adjustment of as little as 2 feet in antenna placement can resolve some noise problems.
High gain antennas will broadcast further, but they may pick up more noise. So keep your cable runs as short as possible, and choose an appropriate antenna.
Polarization matters. All antennas must be polarized the same.
If you have two or more antennas installed next to each other, you may experience noise that prevents good communication. Provide 10 feet of vertical separation from other antennas. (10 ft. of vertical separation can equal up to 30 dB of signal separation.)
When is the best time to complete a Radio Site Survey?
A radio survey should be completed before equipment is ordered or installed because the results of the survey will likely impact the equipment required.
It should be done soon enough before the installation to allow for all pieces of the survey to be completed so the results can be implemented during installation.
Radio surveys should be completed when conditions at the site are representative of normal conditions during the watering season.
Site surveys should be avoided during the winter months because RF signals may not be as robust during the summer when trees are in full foliage compared to winter months when trees are dormant.
If construction is planned on a site that could impede RF Signals, the site should be re-surveyed after construction is complete to account for the changes and necessary changes to equipment.
What do the Signal and Noise numbers mean?
The Signal is the signal strength (in dB) the Endpoint radio is receiving from the radio that it is connected to (the Gateway or the Repeater, depending on your network topology).
The upstream Signal is the signal strength the connected radio (the Gateway or Repeater, depending on the network topology) is receiving from the Endpoint.
The Noise is the local RF noise (in dB) that the Endpoint is hearing at its antenna.
The Upstream Noise is the noise at that connected radio’s antenna.
Both groups of statistics are important. Baseline requires the Signal to be at least 20 dB higher than the Noise (Delta) for both. The bigger the margins, the better.
If the signal level is low (below 40) there may be a line-of-site issue with the antenna. The antenna may need to be redirected or increased in height.
When interference is excessively high (above 70) due to a pager or cellular telephone tower, a band-pass filter may help eliminate this out-of-band noise.