Design

Pre-Enhancement Survey

Each project starts with a pre-enhancement RF survey, during which our engineers gather critical information and documentation about your facility. This includes reviewing building drawings, floor plans, and material types to understand how signals propagate through the structure. The survey identifies areas with weak coverage, interference sources, and potential propagation challenges, providing the foundation for a compliant, data-driven system design.

Equipment Requirements

All Motorola Solutions DAS designs adhere to strict standards that ensure long-term reliability, safety, and compliance:

• All active equipment and battery backups shall be installed in NEMA 4 or 4X-rated enclosures.
• The Bi-Directional Amplifier (BDA) must include oscillation control to prevent interference with external networks.
• All active devices shall provide a minimum of 12-hour battery backup, or 2-hour backup with emergency generator.
• A co-located, dedicated monitor with Fire Alarm Panel integration capability is required.
• Only FCC Type-Accepted equipment is used.
• All coaxial cable in the system must be low-PIM hardline. (Superflex or braided cable is permitted only when a single frequency is used.)
• Outdoor coax must be rated for exterior conditions — never use air dielectric or plenum coax outside.
• Indoor coax must be plenum-rated hardline, installed according to Motorola Solutions specifications.
• Connectors shall be “N,” “DIN,” or “4.3-10” type, and must be low-PIM rated.

Proper Level and Audio Quality

A properly designed DAS provides adequate RF levels, excellent Delivered Audio Quality (DAQ), and a low noise floor. When aligned and commissioned correctly, the system is virtually invisible to the macro network—ensuring no measurable rise in noise while maintaining clear, consistent signal strength for first responders and building personnel.

The Near-Far Effect

In public safety DAS systems, the near-far effect occurs when a portable radio transmitting close to an antenna causes gain reduction that limits distant radios. To prevent this, Motorola Solutions engineers design systems with a higher antenna density rather than excessive power—ensuring uniform coverage and stable communications throughout the facility.

Preventing System Oscillation

System oscillation is one of the most common and serious DAS design errors. It occurs when insufficient isolation exists between the donor antenna and the in-building antennas. Motorola Solutions designs every system to meet or exceed the industry standard for minimum antenna-to-antenna isolation:

Minimum Isolation = BDA Gain + 15 dB
Example: 80 dB BDA Gain + 15 dB = 95 dB minimum isolation

This ensures legal operation, prevents harmful interference, and guarantees stable system performance.

Donor Antennas

Proper donor antenna selection and placement are essential to achieving the right balance between desired signal gain and unwanted interference. Motorola Solutions specifies:

• High-directivity, high front-to-back ratio antennas to reduce unwanted channel power.
• Optimized mounting height—as low as possible while maintaining line-of-sight to the donor site.
• Precise azimuth alignment to target the correct serving tower and minimize noise from distant sites.

Passive Intermodulation (PIM)

Low-PIM components are mandatory in every Motorola Solutions design. PIM results from nonlinearities in passive components—such as loose connectors or corroded metals—that generate unwanted signals which cannot be filtered out.

Motorola Solutions mitigates PIM through:

• The use of certified low-PIM connectors and cables (“N” and “4.3-10”).
• Proper torque and installation practices to ensure consistent contact.
• Avoidance of mixed-metal components or improperly grounded fittings.

Propagation Delay and Time Domain Interference (TDI)

Propagation delay is a normal characteristic of RF boosters and must be accounted for in every engineered design. Motorola Solutions calculates time delay based on filter bandwidth, system topology, and the number of sections within the amplification chain.

• Typical propagation delay: ~5 µs for filters >200 kHz.
• Acceptable time overlap (TDI threshold): ≤33 µs for DAQ 3.4 systems; ≤15 µs for P25 Phase 2 systems.
• Properly designed DAS systems avoid overlap zones by maintaining ≥20 dB dominance between overlapping signals.

Power per Channel Considerations

In broadband amplifiers, total composite output power is distributed across all active channels. To maintain signal quality and avoid overload, Motorola Solutions engineers design with conservative power assumptions and the following best practices:

• Calculate power per channel based on composite signal level, not a single carrier.
• Favor more antennas over more power to prevent near-far imbalance.
• Use only the minimum gain necessary to achieve code-required coverage.
• For active DAS, set BDA gain appropriately for the fiber headend input level.

DAS Uplink Optimization for Noise

A properly commissioned DAS must not raise the noise floor at the public safety donor tower’s receiver. To ensure this, Motorola Solutions engineers carefully balance system gain and uplink attenuation using the following formula:

Total UL Attenuation = 10 log (# of Remotes) + System UL Gain + NF of Remote Band

By matching system path attenuation to the calculated noise rise, the uplink remains transparent to the macro system and maintains maximum sensitivity at the donor site.

Certificates of Occupancy

Final occupancy permits can be denied without proof of adequate radio coverage and system performance. Every Motorola Solutions DAS is designed, tested, and documented to meet or exceed NFPA 1225, IFC, and AHJ requirements—ensuring your building passes inspection and achieves Certificate of Occupancy approval on the first review.

Setting the Standard for Reliable In-Building Communication

Every Motorola Solutions DAS begins with disciplined engineering and an uncompromising focus on safety, performance, and compliance. From the earliest survey data to the final design approval, our process ensures that every component, connection, and calculation supports mission-critical reliability. By adhering to industry standards and Motorola’s own proven design practices, we deliver systems that integrate seamlessly with public safety and enterprise networks—providing clear, dependable communication when and where it matters most.