- How high is the insertion loss of a Combiner?
The insertion loss of a combiner is a determining factor in the selection of the technology used during development of each product. Further criteria in deciding which technology should be deployed in the design of the combiner are the bandwidth of the frequency under consideration, the required isolation between the bands and the power rating.
The insertion loss experienced with Multi-Band Combiners tends to be significantly reduced the further apart the frequencies are. For example, values of 0,1 dB are typical for many Kathrein multi-band combiners where 900 and 1800 or 2100 MHz are being combined. The insertion loss for Multi-Band Combiners for the combining of neighbouring frequencies such as 1800 and 2100, on the other hand, may increase to < 0,3 dB.
Occasionally we are confronted with misconceptions from the field that all combiners have 3 dB insertion losses. In such cases it is generally quite clear that multi-band combining applications have been confused with same-band combining using Hybrid Combiners.
- Why and where are TMA’s deployed in a network?
A Tower Mounted Amplifier (TMA) is often used in order to increase the sensitivity of the receiver in the system. Generally the radio link from the Base Station to the end-user in the cell is satisfactory (downlink). The radio link from the end-user to the Base Station (uplink), on the other hand, is often lower in power and is prone to fading and other site specific effects. This can cause dropped calls. In particular, the Base Station may lose end-users located at the edge of the cell due to poor uplink performance.
TMA’s should be deployed in order to amplify the uplink signal (Rx) directly below and as close as possible to the Rx Base Station Antenna output. Unnecessary lengths of jumper cable between the TMA and the antenna only lead to a reduction in the Signal-to-Noise ratio which is an important criterion in the management of the receiving system sensitivity.
Kathrein offer a variety of legacy TMA products. However, in recent months and years we have seen a revival in TMA business with focus now being set on new TMA’s for LTE applications (800, 1800 and 2600) and also Dual-Band versions, which can be used in conjunction with either existing broad-band antenna or new antenna site configurations.
Please contact your Kathrein Mobile Communication sales partner for details.
- Does Kathrein also supply Boosters or GMAs (Ground Mounted Amplifiers)?
GMAs have essentially the same functionality as TMAs. However, GMAs have the distinct disadvantage of being mounted at the foot of the mast which is often a considerable distance from the receiving antenna system. The Rx signal will be subject to additional losses due to the length of RF feeder cable between the receiving antenna and the GMA. Hence any noise created on the RF path from the antenna to the GMA will be amplified together with the reduced Rx signal. The overall Signal-to-Noise ratio of the system is thereby reduced. For this reason Kathrein does not recommend deployment of GMAs, however, TMAs can theoretically also be used for this type of application.
Boosters increase the output power on the transmitting radio link from the Base Station (downlink). The uplink/downlink balance is of paramount importance when designing a mobile communications site. Care should be taken to ensure that the cell coverage is not biased in favour of either the downlink or the uplink. Generally the downlink from the Base Station to the end-user is not the cause of concern. On the contrary, the uplink from the end-user to the Base Station is more often the reason for dropped calls. In particular, the Base Station may lose end-users located at the edge of the cell due to poor uplink performance. Hence, the deployment of TMAs is much more predominant in the rollout of mobile communication networks. Kathrein Mobile Communication does not supply Boosters.
- How can I select the correct TMA for my network requirements?
Kathrein Mobile Communication offers a wide range of DTMAs for practically all frequency spectrums. In addition, we have a number of additional features on selected DTMAs available which make deployment in multi-band or broad-band antenna configurations possible.
For instance, Kathrein Mobile Communication offer a variety of DTMAs with an RF-Bypass feature so that amplification in one frequency spectrum is possible and the other service is by-passed onto either a separate or common output. This enables feeder sharing without the use of additional combiners.
Alternatively, the deployment of dual-band DTMAs is now also possible, thereby making the retrofitting of existing sites with an additional service a relatively simple exercise.
Please see our selection guide “DTMA Selection Guide” in our customer portal for a full overview.
- How can feeder sharing be performed in spite of a mixed protocol environment at the mast head (CWA, AISG or proprietary communication protocol)?
Legacy site configurations often make use of CWA controlled DTMA’s. In addition certain vendors have, or had, proprietary communication protocols for the control of mast-head devices. Quite often these communication protocols were injected onto the RF feeder cable, decoupled at the mast-head and directly fed into the individual devices.
If additional services are being installed on such existing sites, then the provider is faced with a potential design challenge if existing RF feeders need to be used and multiple communication protocols (AISG 1.1, AISG 2.0, CWA and or vendor proprietary protocol) must operate in parallel via the RF feeders.
Kathrein Mobile Communication have developed special Dual-Band Combiners which solve this issue with a minimum of additional investment. Kathrein’s SmartPlex [78210900/-901] allows the continued operation of legacy masthead devices without any restrictions. In addition, further protocols can be used for additional mast-head devices without separate cable runs. Additional Bias Tees and DC Stops are not required. Our SmartPlex product family offers a cost effective solution for enabling simultaneous multi-protocol communication transparency while allowing RF feeder sharing. The SmartPlex also intuitively provides the correct DC supply voltages where needed.
For further applications please see our „Co siting application notes download“ via the customer portal.
- What is the difference between a Bias Tee and a Smart Bias Tee?
A Bias Tee is used to inject or decouple a DC voltage and, where applicable, also AISG control signals into or from the feeder cable in order to provide operating voltage and, where applicable, controls signals via the RF feeder cable to a TMA or antenna tilting actuator (Remote Control Unit – RCU).
Generally speaking, Kathrein offer three different types of Bias Tees with variants depending on RF operating frequency range:
- Bias Tees where a DC voltage can be injected into, or decoupled from the RF feeder via an SMB male or SMA female connector respectively.
- Bias Tees where a DC voltage together with an AISG control signal, which has already undergone Layer-One-Conversion (LOC), can be injected into the unit via an SMB male connector. In such cases, the AISG signal has already been modulated on a carrier at 2.176 MHz prior to being made available to the Bias Tee input.
- Smart Bias Tees allow injection or decoupling of the DC Voltage and also performs the LOC of the AISG control signal via an internal modem. These units have an 8-pin connector for an RS485 interface and allow direct connection with standard primary and secondary AISG devices via standard RET control cables.