Published on 10/13/2026
Choose n77/n78 coax from its complete-assembly loss and matching across the actual operating band, not from a 3.5 GHz spot check alone. n77 spans 3.3 to 4.2 GHz and n78 spans 3.3 to 3.8 GHz, so a cable specified only at the nominal center can miss the required upper frequencies.
A 5G router moved inside a cabinet may need external antennas and several feeders. Extra cable loss affects each RF path, while incorrect port mapping or a fragile board pigtail creates problems that a larger cable will not fix.
The useful change at 3.5 GHz is stricter attention to total loss, interfaces and installed routing. It is not a reason to choose mmWave connectors automatically.
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n78 lies within the n77 frequency span, but device support, permitted channels and antenna coverage still have to match the application. Specify the required band edges from the device and network requirements, then qualify the assembly over that range.
| NR band | Frequency span | Cable qualification implication |
|---|---|---|
| n77 | 3300 to 4200 MHz | Include 4.2 GHz when the full band is required |
| n78 | 3300 to 3800 MHz | Include 3.8 GHz when the full band is required |
| Nominal 3.5 GHz point | Single test frequency | Not sufficient by itself to prove full-band performance |
These band spans describe the technical band definitions, not a statement that every frequency is licensed or available in every country. A cable specification does not replace radio approval or regional spectrum checks.
Use maximum insertion loss over the required band for the complete installed assembly. Cable length, connector bodies, adapters and routing all belong in the estimate. A nominal RG family does not establish loss at 3.5 GHz, and a datasheet ending at 3 GHz should not be extended by assumption.
| Cable-only allowance | Length | Maximum attenuation |
|---|---|---|
| 1 dB | 0.5 m | 2 dB/m |
| 1 dB | 2 m | 0.5 dB/m |
| 1 dB | 5 m | 0.2 dB/m |
| 2 dB | 5 m | 0.4 dB/m |
Key idea: The table is calculated from example budgets, not a rating for any cable. Use the highest required frequency and the exact cable construction when screening a candidate.
Label each antenna and modem port according to the equipment documentation. Do not assume every external port serves the same bands or that swapping a diversity, GNSS or cellular port is harmless. Connector fit does not establish signal function.
Similar cable constructions and controlled lengths can simplify a multi-path design, but ordinary MIMO does not automatically require a phase-matched cable set. If coherent beamforming or a particular radio design needs phase matching, state the phase tolerance, band and reference planes explicitly.
Step 01
Identify every port
Record the manufacturer's port name, function and supported band. Use the exact intended antenna path.
Step 02
Control the assembly set
Keep part numbers, length references and revision labels consistent. Track loss targets for each path rather than averaging them.
Step 03
Qualify the installed route
Check connector clearance, bend geometry and strain relief with all cables present. A tight cable bundle can move a termination or force a sharper bend.
Specify the loss you can afford, not only the cable name
Send SigmaRF your frequency band, connector interfaces, installed length and insertion-loss target. Every assembly is VNA-swept for VSWR and insertion loss before shipment.
Specify a Custom AssemblyA compact modem board may use a miniature interface such as an MHF-type connector. Identify the exact series from the drawing; do not buy a lead only by an IPEX nickname. Keep the board lead supported and use the specified mating procedure.
A panel interface can let a larger external feeder carry the long route without loading the board connector. SMA can be suitable for sub-6 GHz when the exact part and cable termination meet the band and mechanical requirements. Other systems may require N-type or another interface. Frequency alone does not choose the connector.
For outdoor equipment, specify jacket exposure, connector sealing, strain relief and any grounding or protection requirements from the installation design. Low insertion loss is not proof of low PIM; where passive intermodulation is required, state its separate test conditions.
An RFQ should name band edges, impedance, both connector interfaces, complete assembly length, maximum insertion loss and required VSWR. Add temperature, exposure, routing, test report and path labels. Phase matching and PIM are additional requirements only when the system needs them.
Read SigmaRF's Cellular Repeater and DAS Cable Selection guide for building feeds, Phase-Matched Cable Assemblies for coherent applications and Passive Intermodulation for separate PIM qualification. This article focuses on n77/n78 device-to-antenna paths.
Illustrative n78 feeder: 3 m route, 1.5 dB maximum complete loss over the required band, and an assumed 0.3 dB total interface allowance.
The candidate loss is an assumption, not a published cable rating. Verify each completed path across the requested band. A 0.50 dB loss difference is a measured power imbalance if those assembly losses are verified; it is not by itself a prediction of MIMO throughput.
What frequency range does n78 use?
The n78 band spans 3300 to 3800 MHz. Specify the actual required device and network range and check regional operating permissions separately.
Is n77 the same as n78?
No. n77 spans 3300 to 4200 MHz, while n78 spans 3300 to 3800 MHz. Their overlap does not prove that a device supports both bands.
Can I use SMA for 3.5 GHz 5G?
A suitable exact SMA part can serve this band when its termination, matching and loss meet the requirement. Confirm the hardware interface and complete assembly ratings.
Do MIMO antenna cables need equal lengths?
Follow the radio design requirements. Consistent routing and loss may matter, but ordinary MIMO does not automatically require phase-matched cables. Specify phase only when the system needs it.
How much coax loss is acceptable for n78?
Use the radio link budget and antenna arrangement to set the maximum loss. There is no universal dB limit; qualify each assembly over the required band.
Does VNA testing prove low PIM?
No. VSWR and insertion loss are linear RF measurements. PIM needs its own specified test with defined tones, power and acceptance limit.
For n77/n78, specify full-band assembly performance and keep every antenna path correctly identified. Small internal leads and long external feeders need different mechanical treatment, even when they share the same 50 ohm system.
SigmaRF VNA-sweeps every assembly for VSWR and insertion loss before shipment. Requirements span 100 MHz to 40 GHz through Vadodara volume and Cleveland-area precision facilities. Lead times can be as short as 2 days for suitable builds; confirm materials and any extra qualification requirements.
Specify the loss you can afford, not only the cable name
Send SigmaRF your frequency band, connector interfaces, installed length and insertion-loss target. Every assembly is VNA-swept for VSWR and insertion loss before shipment.
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