Breaking Down an
In-Building Communication System

In-building systems provide an RF signal inside buildings.  They basically consist of a signal initiator (donor antenna, access point) and a product to enhance existing signals (signal booster, BDA).  The RF signal is distributed inside the building by a Distributed Antenna System (DAS) and use of coax(passive) or fiber/coax hybrid (active).  The goal of a successful distribution system is to provide the following:

1. Coverage to customer specification

2. Uniform coverage

3. Minimal cable expense

Boosters or Bi-Directional Amplifiers come in two types

1.  Channelized  (FCC Class A) -   pass specific channels in each direction.

Channelized versions only pass specific radio channels on a channel by channel basis. These are useful when the RF spectrum is congested and multiple undesired carriers are intermixed with desired carriers.  These types of boosters offer a higher output power per channel, decoding/encoding functions, and frequency programmability.  In addition, loss of a single channel module only affects that specific channel.  However, disadvantages include a fixed number of channels, higher costs and a higher group delay than what is found in broadband boosters.

2.  Broadband   (FCC Class B)  -  passes a range of frequencies

In a broadband signal booster, the maximum output level, and level of any spurious components, is controlled by the OLC (Output Level Control) circuitry.  The OLC circuit monitors the composite output power of the booster.  It does nothing up until the point that the booster reaches its rated output power.  If the input signal to the booster then increases, the OLC circuit simply begins adding attenuation into the low level amplifier chain to keep the output power from increasing above its rated value.

Keep in mind:

UHF (450-512 MHz) frequencies have a defined band plan.  Broadband boosters are pre-manufactured to accommodate these frequencies.  However, a channelized BDA may be more appropriate in high RF areas to avoid congestion.


VHF (140-174 MHz) frequencies have no defined band plan and it is common to have multiple, interleaved uplinks and downlink passbands.  It is for this reason that there are no "standard" model VHF signal boosters they are all custom made.

• Great for "open" areas
• Use in areas where corridors are numerous and short
• Better wall penetration coverage

2.    Radiating Cable

• Good for tunnels, corridors and similar applications.
• Uniform coverage along length of cable
• Typically good coverage at 50 feet from cable

3.    Fiber Cable

• Cost effective option when a very long run of cable is required
• Converts signals to light and transports over the fiber optic cable
• Offers minimal RF loss--which limits the distribution loss

4.    Special Devices used to feed the signal to multiple internal antennas

• Splitters-used to distribute signal between floors or different coverage paths
• Hybrid coupler - used to "balance" the system internally
• Cross-band Coupler-required to distribute different bands through DAS

5.    Combination of the above