Published on 10/13/2026
A GNSS receiver loses satellites after its antenna is moved to a roof with a longer cable. The immediate temptation is to add an amplifier. Before changing hardware, inspect the antenna type, cable loss, bias supply and receiver input requirements.
Choose GNSS coax by the loss and gain budget of the complete antenna path, not by a universal maximum length. Active antennas have an LNA before the cable; passive antennas do not. Cable loss before the first LNA is especially costly to receiver noise performance.
For multiband GNSS, qualify the path over every required band. A cable that is acceptable for one signal band may have different loss and antenna-chain gain at another.
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A passive antenna delivers its weak signal directly through the cable to the receiver. Loss before the receiver's first amplification reduces available signal-to-noise performance. An active antenna places an LNA near the antenna element and usually receives DC power through the same coax.
The antenna LNA reduces the relative noise contribution of later stages when its gain is sufficient. It does not repair a poor antenna radiation pattern, blocked sky view or multipath. Excess gain can overload the receiver, so respect the receiver's allowed input gain and signal levels.
| Path | Main cable concern | Additional checks |
|---|---|---|
| Passive antenna | Minimize loss before first LNA | Receiver noise figure and antenna match |
| Active antenna | Loss after LNA and net input gain | Bias voltage/current, overload and filtering |
| Multiband active antenna | Budget every required band | Antenna/LNA response and receiver support |
Start with antenna LNA gain at each band, then subtract cable, connector, adapter and surge-protector loss. Compare the resulting gain with the receiver's recommended range. Use minimum and maximum values where available, not only typical figures.
GPS L1 is centered at 1575.42 MHz and GPS L5 at 1176.45 MHz. A multiconstellation antenna may need a wider passband than those two center frequencies. Specify actual antenna and receiver bands rather than copying a narrow center-frequency test.
Do not treat active-antenna total gain as antenna element gain. Element gain, LNA gain and noise figure describe different properties. Record them separately when available.
Key idea: Antenna gain in dBic and amplifier power gain in dB are not interchangeable. More amplifier gain cannot restore information lost by a poor antenna.
Get the interface right before ordering
Send the equipment-port details, cable length and operating band to SigmaRF.
Specify a Custom AssemblyAn active antenna must receive the required voltage after cable and connection drop. Determine loop resistance from both center conductor and return path, then multiply by antenna current. Confirm supply limits, short protection and whether every adapter or protector passes the required DC.
Use the correct connector and polarity. Standard SMA and RP-SMA can look similar but have different contacts; do not identify a GNSS port from application alone. Specify both cable ends explicitly.
For outdoor runs, include seals, UV-rated jacket, grounding and suitable surge protection in the design. A surge device may add RF loss and may block DC or a required GNSS band. Verify its complete specification, not only its connector type.
Thin coax suits short pigtails and tight routing; larger low-loss feeders suit longer fixed runs. The useful crossover depends on the receiver and antenna budget, not a generic meter count. Keep unsupported adapters away from small ports.
Timing applications may require known cable delay and calibration or receiver compensation. Cable length does not create a simple universal positioning-error formula. Surveying and precision positioning also depend on antenna placement and phase-center behavior.
Read SigmaRF's GPS L1 vs L5 guide for multiband considerations and its antenna-LNA placement guide for noise cascades. This article focuses on the cable budget and bias path.
A hypothetical active GNSS antenna has 28 dB LNA gain at the required band. Cable and accessories are assumed to have measured losses below. These values are not a universal receiver requirement.
Check whether 22.2 dB fits the actual receiver's input-gain requirements and whether the antenna receives sufficient voltage. Repeat at all bands and over tolerances. Net gain alone does not establish system noise figure or overload immunity.
How long can a GPS antenna cable be?
There is no universal length limit. Use the active or passive antenna path, cable loss, receiver gain requirements and DC bias limits to determine the acceptable run.
Does an active GPS antenna eliminate cable loss?
No. The LNA provides gain before the cable and can reduce later-stage noise impact. Cable loss still changes net gain and can matter to bias supply and receiver performance.
Should I use RG174 or thicker coax for GNSS?
Use thin coax where length and routing allow its loss. Use a lower-loss feeder when the run consumes too much budget. Choose from exact cable data and complete assembly measurements.
Can a GPS surge protector block antenna power?
Some devices block DC; others pass it under specified limits. Confirm DC path, current, insertion loss and all required GNSS bands before installing.
Does GPS cable length affect accuracy?
Cable loss can degrade reception, and delay can matter for timing. Positioning accuracy also depends on antenna placement and system design. There is no simple universal error-per-meter cable rule.
Do dual-band GNSS cables need separate testing?
The same coax can carry both bands, but test its match and loss across every required band and check the antenna chain's gain at each.
Choose the cable as part of the antenna system. Keep antenna element performance, first-stage noise, feeder loss, receiver gain and DC bias separate in the budget.
A useful RFQ names the bands, maximum cable loss, connector details, antenna current and installation conditions. That is more useful than asking for the longest possible GPS extension.
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.
Get the interface right before ordering
Send the equipment-port details, cable length and operating band to SigmaRF.
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