Comba CriticalPoint 700/800 MHz Class A Public Safety Bi-Directional Amplifier

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Product Description

The Comba CriticalPoint Public Safety Class A Bi-Directional Amplifier (BDA) provides consistent signals for crucial First Responder communications.

The Comba CriticalPoint can be configured by our signal experts for any Public Safety installations. It is a a 700MHz/800MHz single or dual band digital channelized repeater that supports up to 32 channels per band. Depending on the size of the building, the BDA is offered in two versions, a .5W or 2W of downlink power per band to accommodate smaller buildings. The unit can be either AC or 48V DC powered depending on installation needs. It is fully compliant with IFC and NFPA (National Fire Protection Association) requirements.

Channelized uplink Automatic Gain Control (AGC) ensures minimum interference to cell towers and optimizes quality and coverage.

The CriticalPoint features comprehensive alarming capabilities, which supports all NFPA and IFC required monitoring and alarming, and also provides local and SNMP based remote monitoring. The built-in signal generator and isolation testing function make deployment by system integrators convenient and straightforward.


  • Single or dual band configuration (700MHz/800MHz)
  • Supports up to 32 channels per band
  • 2W output power for each band. ½W version available.
  • Channelized uplink (AGC)
  • Channelized uplink squelch supported
  • Web based GUI for simple configuration
  • Built-in mandatory isolation test to prevent BDA oscillation
  • NFPA compliant dry contact alarms
  • NEMA 4 enclosure

Comba products are commercial level, not consumer level products. Comba products cannot be installed, commissioned or put on air unless done so by an authorized, trained and certified Comba Systems Integrator. In certain cases, the Systems Integrator will need permission from appropriate authorities to put the Comba equipment on air. Any person or organization that puts Comba equipment on air without the appropriate permissions, and without the required authorization and certification by Comba Telecom will be in violation of FCC and/or other jurisdictional laws.

What is a channelized booster?

Signal boosters, also called amplifiers and cellular repeaters, are hardware devices that are “bi-directional amplifiers”. They amplify the signal being sent to and from the nearest cellphone tower. The FCC defines bi-directional amplifiers (BDAs) in two classifications:

Class A signal booster. A signal booster designed to retransmit signals on one or more specific channels. A signal booster is deemed to be a Class A signal booster if none of its passbands exceed 75 kHz.
Class B signal booster. A signal booster designed to retransmit any signals within a wide frequency band. A signal booster is deemed to be a Class B signal booster if it has a passband that exceeds 75 kHz.

A Class A booster is also known as a “channelized” or “channel selective” booster. A Class A booster is a narrowband booster that is capable of single channel selectivity.

A Class B booster is a broadband booster that amplifies a group of channels that fall within a given frequency range.  All Class B Signal Boosters devices must be registered with the FCC so they can be managed and shut down if found to cause interference. 

Most of the latest BDAs are now digitally-programmable and feature software that can narrow and target particular frequencies. The user can vary the passband bandwidth for each channel or a group of channels. If the channel filters are set to 75KHz bandwidth or narrower, the FCC classifies the unit as a Class A narrowband BDA. When the device channel filters are set for wider than 75KHz, it is considered a Class B broadband device. 

What are the benefits of a channelized booster?

Channelized boosters amplify only discrete frequencies. All other signals are attenuated and have little or no affect on the power available to the desired channels. This prevents a near-far effect from overpowering the booster system.

The near-far effect occurs when a user wishes to amplify a particular channel, but there are other, stronger channels on the same frequency. Since the strongest channels will determine the BDA’s overall gain, the desired frequency could actually receive 10-20+ dB less gain, and hence less power, than the interfering frequencies.

Class A devices are generally not so straightforward to set-up as Class B devices. Class A BDAs require all desired frequencies to be entered individually. But the additional benefit of this is that Class A devices allow for more in-depth customization. User settings available in Class A devices but not typically available in Class B include individual channel gain, squelch, and bandwidth options.  

Channelized boosters are generally more reliable than broadband boosters. As well as the near-far effect described above (where they filter out undesired channels that could reduce amplifier power from desired channels), they also have dynamic or adaptive gain circuits that can absorb minor fluctuations in signal levels while maintaining stable output levels. Broadband BDAs can experience significant fluctuations in output power based on channel loading in the wideband RF environment. These fluctuations can adversely affect in-building coverage and the reliability of first responder radio communications. 

Class A channelized boosters also have less problems with noise than Class B boosters. They have independent amplifier circuits that can remain silent until a radio is keyed from within the building, meaning only active channels are transmitted back to the donor site. A Class B device, by contrast, is always on, even with no radio traffic inside the building, always amplifying noise. The CriticalPoint Class A BDA will go completely silent and generate no noise until radio traffic appears. 




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