A Split Mount Microwave Radio consisted of Indoor plus Outdoor components – specifically Indoor Unit (IDU) and Outdoor Unit (ODU)
Split Mount Microwave Radios offer up to 500 Mbps and 1Gbps Full Duplex payload and higher up to 6Gbps or more, in 4-42GHz licensed frequency bands.
Indoor Unit (IDU)
A Typical Split Mount Radio consists of a 19″ Rack Mount Indoor Unit which is mounted in a rack, cabinet, comms room, or even roof-mount shelter as possible locations.
Outdoor Unit (ODU)
The Outdoor Unit (ODU) is typically mounted directly to the Microwave Antenna on a rooftop or tower location, which enables clear Line of Sight (LOS) between both ends of the Microwave link.
For most bands above 6GHz the ODU has a waveguide interface which enables efficient, low-loss connection directly to the antenna. For lower bands below 6GHz, commonly a coaxial cable is used between the ODU and the antenna.
In certain cases, the ODU can be remote mounted from the antenna, and a waveguide used to connect between them
Comparison with Full Outdoor Radios
A split mount radio is considered a “traditional” design and older radios always feature this. The Indoor Unit has all the network interfaces and processing in the easy-access indoor location at the foot the tower or building. Full Outdoor Radios by contrast have all the active items including the modem and user network interfaces inside the rooftop radio element. This saves on space, materials, installation time and cost. A downside is that in the event of any failure, a tower climb is almost always needed to rectify any fault, which may be impossible in rough weather, or require permits or have access limitations to reach
Distances and Range Capability of Split Mount Radios
Using suitable antennas and sites, ultra-long-distance links exceeding 100km can be achieved. Distances depend on:
Required throughput (Mbps)
Desired Availability (%)
Antenna size (gain)
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The term ODU is used in Split-Mount Microwave systems where an Indoor Unit (IDU) is typically mounted in an indoor location (or weatherproof shelter) connected via a coaxial cable to the ODU which is mounted on a rooftop or tower top location.
Often the ODU is direct mounted to a microwave antenna using “Slip fit” waveguide connection. In some cases, a Flexible Waveguide jumper is used to connect from the ODU to the antenna.
The ODU converts data from the IDU into an RF signal for transmission. It also converts the RF signal from the far end to suitable data to transmit to the IDU. ODUs are weatherproofed units that are mounted on top of a tower either directly connected to a microwave antenna or connected to it through a wave guide.
Generally, Microwave ODUs designed for full duplex operation, with separate signals for transmit and receive. On the airside interface this corresponds to a “pair” of frequencies, one for transmit, the other for receive. This is known as “FDD” (Frequency Division Duplexing)
ODU Power and data signals
The ODU receives its power and the data signals from the IDU through a single coaxial cable. ODU parameters are configured and monitored through the IDU. The DC power, transmit signal, receive signal and some command/control telemetry signals are all combined onto the single coaxial cable. This use of a single cable is designed to reduce cost and time of installation.
ODu Frequency bands and sub-bands
Each ODU is designed to operate over a predefined frequency sub-band. For example 21.2 – 23.6GHz for a 23GHz system, 17.7 – 19.7GHz for a 18GHz system and 24.5 – 26.5GHz for a 26GHz system as for ODUs. The sub-band is set in hardware (filters, diplexer) at time of manufacture and cannot be changed in the field.
1+0, 1+1, 2+0 Deployments
Microwave ODUs can be deployed in various configurations.
The most common is 1+0 which has a single ODU, generally connected directly to the microwave antenna. 1+0 means “unprotected” in that there is no resilience or backup equipment or path.
For resilient networks there are several different configurations. 1+1 in “Hot Standby” is common and typically has a pair of ODUs (one active, one standby) connected via a Microwave Coupler to the antenna. There is typically a 3dB or 6dB loss in the coupler which splits the power either equally or unequally between the main and standby path.
Other resilient configurations are 1+1 SD (Space Diversity, using separate antennas, one ODU on each) and 1+1 FD (Frequency Diversity)
The other non-resilient configuration is 2+0 which has two ODUs connected to a single antenna via a coupler. The hardware configuration is identical to 1+1 FD, but the ODUs carry separate signals to increase the overall capacity.
Grounding & Surge Protection
Suitable ground wire should be connected to the ODU ground lug to an appropriate ground point on the antenna mounting or tower for lightning protection. This grounding is essential to avoid damage due to electrical storms.
In-line Surge Suppressors are used to protect the ODU and IDU from surges that could travel down the cable in the case of extreme surges caused by lightning
The specification of a typical Microwave ODU is shown below.
Typical ODU Features and Specifications:
4-42GHz frequency bands available
Fully synthesized design
3.5-56MHz RF channel bandwidths
Supports QPSK and 16 to 1024 QAM. Some ODUs may support 2048QAM
Standard and high power options
High MTBF, greater than 92.000 hours
Software controlled ODU functions
Designed to meet FCC, ETSI and CE safety and emission standards
Supports popular ITU-R standards and frequency recommendations
Software configurable microcontroller for ODU monitor and control settings
Low noise figure, low phase noise and high linearity
Compact and lightweight design
Very high frequency stability +/-2.5 ppm
Wide operating temperature range: -40°C to +65°C
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