System Design Concepts

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System Design Concepts

• By Gus Roumeliotis

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System Design Concepts

• Antenna Combining Systems
• Allow multiple transmitters and receivers to
  share an antenna system
• Provide adequate isolation to permit simultaneous
  operation of all frequencies
• May consist of several antenna systems (multiple
  Tx Rx antennas)
• Terminology
• Multicoupling
• Refers to the combining of multiple transmitters
  and receivers onto a single antenna.
• Combiner
• Transmit multicoupler with ferrite isolators

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System Design Concepts

• Advantages
• Maximize tower utilization
• Reduces tower loading by minimizing the number of
  antennas feedlines
• Expandable systems avoid need for tower climb
• Premium antenna location can be utilized by many
  users
• Minimize interference risk
• Proper multicoupler system is designed to avoid
  all transmitter noise, receiver desense, and
  intermod problems
• Bandpass filters commonly used in multicoupler
  systems to provide carrier suppression against
  other transmitters and noise suppression to avoid
  causing problems for receivers.
• Bandpass filters also inherently notch the second
  harmonic of the pass frequency

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System Design Concepts

• VHF systems
• Virtually no band plan
• Potential for extremely close Tx-Rx spacings
• Most Tx combiner and Rx Multicoupler systems are
  custom designs
• Lower frequency means separation must be greater
  between antennas
• 30-40 feet tip-to-bottom to gives approx. 55 dB
• Greater cavity efficiency in this frequency band.
• 7 bandpass cavity set at 1.0 dB insertion loss
  will provide 20 dB isolation 1.0 MHz from f0
• UHF Systems
• Paired services mean standard spacings
• Watch for close minimum spacings
• E.g. 461 Tx and 459 Rx
• Higher frequency means separation can be less
  between antennas
• 20 feet tip-to-bottom to get 55 dB
• Lower cavity efficiency at this higher frequency
  band.
• 7 bandpass cavity set at 1.0 dB insertion loss
  will provide 12 dB isolation 1.0 MHz from f0

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System Design Concepts

• 800 900 MHz systems
• Paired services mean standard spacings
• Watch for cell sites and paging transmitters
• 894 MHz is 2MHz from 900 MHz SMR Rx band
• Higher frequency means separation can be less
  between antennas
• 10 feet tip-to-bottom to get 55 dB
• Use of ¾ wavelength cavities required
• 7 ¾ wave bandpass cavity set at 1.0 dB insertion
  loss will provide 11 dB isolation 1.0 MHz from f0

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System Design Concepts

• The Antenna Combining System Design Objectives
• Provide sufficient isolation between transmitters
  (Txs) and Receivers (Rxs) to prevent RF
  interference in each receiver
• Tx/Rx (Transmitter noise)
• Rx/Tx (Receiver desensitization or Tx carrier)
• Tx/Tx (Transmitter to transmitter isolation)
• Rx/Rx (Receiver to receiver isolation)
• Maintain proper impedance match with radios
  (Z050 OHMS)
• Minimize insertion losses

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System Design Concepts

• The Antenna Combining System Design Constraints
• Number of Transmitters (Txs) and Receivers
  (Rxs)
• Frequency of Txs and Rxs (MHz)
• Tx power levels (Watts)
• Radio manufacturers (Motorola, GE, Kenwood)
• Number of antennas (Gain of antennas in dBd)
• Horizontal or Vertical antenna separation (Feet)
• Future expansion needs
• Packaging
• Other operating frequencies on site
• Combine or mate with existing equipment
• Desired Price and availability

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System Design Concepts

• The Antenna Combining System Design Process
• Obtain design constraint information
• Txs Rxs frequencies, power levels, antennas,
  etc.
• Perform intermodulation study
• Examine frequency separations
• Tx/Rx, Rx/Tx, Tx/Tx, Rx/Rx
• Determine isolation requirements
• Duplex operation curves (TNRD Curves)
• Select type(s) of components and/or combiners to
  be utilized
• Sketch design configuration using Visio
• (Electrical and Mechanical)
• Verify all design constraints incorporated and
  objectives met
• Price system up, and check system availability
• Finalize system diagram/quotation

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System Design Concepts

• Sinclair Capabilities
• Custom combining and multicoupling systems
  available
• Complete line of components for embedding into
  OEM systems
• Cavity filters
• Duplexers
• Preselectors
• Isolators
• Preamplifiers
• Splitters

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System Design Concepts

• Custom Special Requirements
• Simplex, half-duplex, full duplex radio combining
• High power transmitters
• High isolation/low loss
• Small packaging
• Cabinet systems
• Various power supply configurations
• Large channel capacity combiners
• Intermod analysis prevention
• Isolation analysis design
• Retuning expansion capabilities
• Expansion/modification of existing antenna system
• Environmental protection
• Customized products (NPRs, RD, etc.)