Cellular Repeater and DAS Cable Selection: In-Building Coverage Guide

Published on 10/13/2026

A cellular booster has strong donor signal outside, but a distant indoor antenna still delivers weak coverage. The branch includes a long feeder, splitter and several transitions. Turning up gain may create a new isolation problem instead of fixing the branch budget.

Choose repeater and DAS cables by the actual cellular bands, complete branch losses, power, PIM requirements and equipment approval constraints. A lower-loss cable can help, but it does not establish donor quality, antenna isolation or legal authority to operate a booster.

This guide distinguishes a small repeater installation from an engineered distributed antenna system. Follow the selected system design and approved component requirements rather than treating every in-building network as interchangeable coax.

Identify the system architecture

A repeater amplifies received cellular signals and retransmits them through a supported antenna system. A passive DAS distributes RF through feeders, splitters, couplers and antennas. Active or hybrid systems add other transport and amplification elements. The cable budget must match the actual architecture.

Budget every branch, not just the bulk cable

Multiply cable attenuation by route length at each required band, then include connectors, splitters, couplers and any other inline parts. Splitter data may state total port insertion loss or excess loss; do not add the ideal splitting loss twice. A two-way equal splitter has an ideal division of about 3.01 dB before excess loss.

Different branches may have different losses. Balance the network according to the design rather than forcing equal physical cable lengths. An antenna on a short branch can receive more power than one at the far end, and indoor coverage also depends on building layout and antenna pattern.

Higher-frequency cellular bands can impose greater feeder loss than lower bands. Verify the complete required span, not a single center frequency or a broad "5G cable" label.

PIM and connector condition need separate evidence

Passive intermodulation can arise at nonlinear passive junctions and produce unwanted products in receive bands. Connector condition, materials, contamination, corrosion and loose contacts can matter. A good insertion-loss or VSWR result does not establish a low-PIM assembly.

Specify PIM test tones, power, units and acceptance limits where required. Do not quote a universal dBc number without test conditions. A PIM result in dBc depends on the reference power, while dBm is an absolute power quantity.

Use qualified interfaces and assembly procedures. Correct torque, clean contacts and supported cable prevent avoidable degradation. Do not claim that replacing one jumper makes the complete DAS low-PIM if splitters, antennas and other joints remain unqualified.

Respect isolation, authorization and building requirements

Repeater donor and indoor antennas need the system's required isolation. Insufficient isolation can cause oscillation or automatic gain reduction. Cable loss is not a substitute for an approved antenna layout and isolation assessment.

Booster rules are jurisdiction-specific. In the United States, consumer-booster operation includes provider consent, registration and use of manufacturer-approved antennas and cables. Elsewhere, verify the applicable authorization and operator conditions. A custom cable should not be substituted where the equipment approval requires a specific configuration.

Building fire and smoke requirements must be checked for the actual route. Outdoor weather resistance does not establish riser, plenum or other building suitability. Read SigmaRF's PIM guide for nonlinear junctions and its cable-loss guide for feeder calculations.

Worked engineering example

A hypothetical passive branch has 10 m of cable with assumed 0.15 dB/m loss at the target band, a two-way splitter with specified total port loss of 3.5 dB and 0.4 dB of other transitions.

These are illustrative values, not a coverage prediction or permitted-power setting. Repeat for every band and branch, and evaluate antenna isolation, coverage and approved operating conditions separately.

Mistakes to avoid

Frequently Asked Questions

Bottom Line

Specify the cable from the complete system budget and approval conditions. Keep loss, PIM, isolation and legal operation separate, because passing one does not establish the others.

For an RFQ, send branch lengths, bands, interfaces, power, PIM limits, building route and approved configuration constraints. That lets the assembly fit the network rather than forcing the network to fit a convenient cable.

SigmaRF VNA-sweeps every assembly for VSWR and insertion loss before shipment. Its testing capability spans 100 MHz to 40 GHz; each assembly is specified for its own operating band. Builds are supported by the Vadodara volume facility and Cleveland-area precision facility. Lead times can be as short as 2 days, depending on the build and component availability.