CDU coupling distribution unit The combining part combines the two carrier frequencies and outputs them to the antenna port; When the carrier frequency exceeds 2, it can be used together with SCU. The combined insertion loss of the CDU is 4.5dB (4.5dB refers to the attenuation near the central frequency band, and the total loss in the whole frequency band is not more than 5.5dB).
Because it is a hybrid combination with full band bandwidth, it supports RF frequency hopping.
2. Shunt function
The branch part consists of two branches, the main receiving branch and the diversity receiving branch.
When the carrier frequency is greater than 4, the splitter can be cascaded into one to eight splitters.
3. Detection and alarm function
The CDU has a standing wave detection function to monitor the status of the antenna feeder. When the detected standing wave exceeds the predetermined threshold (1.5: 1 or 2.5: 1), the CDU will give corresponding alarm signals and indications.
When the internal amplifier and tower amplifier work abnormally, the CDU reports the alarm signal to the OMU.
When the CDU and SCU are used together, if the number of cell carriers is not more than 8, two feeders and one feeder can be used Dual polarized antenna (or 2 unipolar antennas) to transmit and receive signals. 
Scu simple combining unit The four carrier frequencies are combined into one output through three 3dB bridges, and the insertion loss is 6.8dB.
Edu enhanced duplex unit 1. Multiple transmitting signals and multiple receiving signals can share one antenna to reduce the number of antenna feeders.
2. Complete the duplex of receiving and transmitting signals, combining and filtering of transmitting signals.
3. Complete the filtering, low-noise amplification and shunt of the received signal.
4. It provides the feed circuit function of the tower amplifier: including CDU, SCU and EDU modules.
type | Combined mode | Typical value of transmission and insertion loss (dB) | Price comparison (per carrier frequency) |
CDU | Two in one Level 1 3dB bridge | four point five | in |
SCU | Four in one 2-stage 3dB bridge | six point eight | low |
SCU+CDU | Four in one 2-stage 3dB bridge | eight | low |
EDU | Non circuit duplex mode | one | in |
Dual CDU (without circuit breaker) | Non circuit dual CDU mode | one | high |
Dual CDU (without circuit breaker) | Combined dual CDU mode | four point five | in |
1. Basic scheme: adopt the usual CDU+SCU scheme (price first);
2. When the cell has one to two carriers and wide coverage is required: EDU scheme;
3. When the cell has more than three to four carrier frequencies and requires wide coverage: dual CDU scheme;
Limitations of using EDU:
The EDU is only suitable for the situation that each sector is no more than 2 carriers, and needs to be replaced during capacity expansion;
Suggestions for using EDU:
1) Only for areas with little expansion potential;
2) Not recommended in urban areas. If there is wide coverage of two carriers in urban areas, it is recommended to use the dual CDU mode;
3) For directional stations in general, the combiner loss of each sector should be basically the same, and there should be no mixed use of EDU, CDU or even SCU at the same site, or the use of concentric circle technology;
4) EDU is only used in areas with wide coverage needs.
