Cavity Filter-Ferrite vs Hybrid-Ferrite Combining: What’s the Difference?
Transmitter (TX) Combiners are designed to allow a number of transmitters to share a common antenna reducing cost as well as tower wind and weight loading. A TX Combiner needs to accomplish three things:
- Couple two or more channels to one antenna at the lowest practical insertion loss.
- Provide isolation between channels to prevent coupled power from causing intermodulation distortion.
- Provide good output return loss for maximum power transfer to the antenna.
Two types of TX Combiners are used to accomplish routing multiple transmitters to a common antenna; Cavity Filter-Ferrite and Hybrid-Ferrite Combiners. A Filter-Ferrite Combiner is comprised of two or more single or dual stage isolators, and a cavity resonator in each branch which is then connected in parallel with either a daisy-chain or star junction phasing harness. A Hybrid-Ferrite Combiner is comprised of two
or more single or dual stage isolators, harmonic filters, and a hybrid coupler. Additional Bandpass or Pass Notch cavities may also be added to either TX combiner to provide, or improve, transmitter wide band noise suppression for collocated receivers.
Cavity Filter-Ferrite Transmitter Combiners allow for good transmit-to-transmit and antenna-to-transmit isolation with low insertion loss. Understandably, keeping insertion loss low is preferred, as when TX channel spacing becomes too close together the resulting impact to total system performance is poor output return loss and greater power coupled to the isolator output loads from the adjacent channels. In
such cases, the wise choice is to suffer the higher insertion loss of a Hybrid Ferrite Combiner solution to improve output return loss, maximize TX-TX isolation, reduce planned maintenance, and improve the life expectancy of your investment.
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EMR has been designing In-Building systems for decades and we have yet to see a system not meet the communication needs of the application.
“I have been doing BDA and DAS design for 25 years and have yet to have a system not meet the communication needs of the application. There have been times where modifications were required post installation due to unknown, unforeseen, or undisclosed circumstances but we’ve always been able to make the system changes necessary to meet the customer’s needs.” – Doug Ferrini, VP of Engineering.