GPS and GNSS satellites orbit roughly 20,000 km overhead, and by the time their signal reaches your antenna it has fallen to somewhere around −130 dBm, weaker than the noise floor of the receiver trying to capture it. A link budget is the running tally of every gain and loss between the satellite and your receiver, antenna gain, cable loss, splitter loss, and LNA gain, that determines whether your signal survives the trip. Pick too little LNA gain and cable loss buries your signal before it arrives. Pick too much and you risk overloading the receiver's front end.
Use the calculator below to work out the LNA gain your specific link budget needs. We cover the underlying principles in more detail in Your LNA Gain Is Not Free: Getting the GPS Gain Budget Right.
GNSS LNA Gain & Link Budget Calculator
Enter your cable run and splitter configuration to calculate your link budget and find the LNA gain that fits.
Why Placement Matters as Much as the Number Itself
One detail trips up more installations than any single spec: where the LNA sits in the chain. The correct order is Antenna → LNA → Cable → Splitter → Receiver, not the LNA buried somewhere downstream near the receiver.
This isn't a matter of taste. By the Friis cascade formula, the first active gain stage in a link budget dominates the noise figure of everything that follows it. An LNA mounted right at the antenna, ahead of the cable run, suppresses the noise contribution of the cable, the splitter, and the receiver itself, all at once, simply by getting there first. Move the LNA to the end of the chain and the cable and splitter losses degrade your signal-to-noise ratio before the amplifier ever gets a chance to help.
If you only take one thing from this post: mount your LNA at the antenna, not at the receiver end of a long cable run.
How the Calculator Gets to Its Number
The recommendation is a simplified link budget: four numbers added together.
- A baseline gain margin (default 20 dB), the gain needed so the LNA's own noise figure dominates the system rather than whatever sits downstream of it. This figure isn't arbitrary: a phased array radar receiver design study found 18 dB of front-end gain sufficient to take care of overall system noise figure, while u-blox's own GNSS antenna application note uses 25 dB in its reference noise budget calculation. Published GPS receiver patents run higher still, 30 to 40 dB, typically because those architectures have more downstream loss (mixers, IF filters) to suppress than a simple antenna-to-receiver run.
- Cable loss, which varies by cable type and run length. At L1 (1575.42 MHz), typical loss runs anywhere from about 0.1 dB per metre for low-loss cable like LMR-400 up to 0.5 dB per metre for thin, flexible cable like RG-174.
- Splitter loss, if you're feeding more than one receiver from a single antenna.
- Connector and miscellaneous loss, a small allowance for the connectors in your run.
Add those together and you get a recommended gain centered on a specific number, with a few decibels of range on either side to give you room to pick the closest matching part rather than needing an exact, impossible-to-source figure.
A Worked Example
Say you're mounting a GNSS antenna on a rooftop, running 15 metres of medium-loss coax down to a 2-way splitter feeding two receivers. That's 15 m × 0.25 dB/m = 3.75 dB of cable loss, plus 3.5 dB of splitter loss, plus a typical 0.5 dB for connectors, for 7.75 dB of total loss. Add the 20 dB baseline and you land at roughly 28 dB of recommended LNA gain, right at the upper edge of our 25 dB GNSS LNA and a good match for our 27 dB version.
Compare that to a short bench setup, an antenna sitting a metre or two from a single receiver with no splitter. Loss is negligible, so the recommendation sits close to the 20 dB baseline alone, which is exactly why a simple bench setup and a real rooftop installation call for noticeably different LNA gain even though both are technically "a GNSS antenna feeding a GNSS receiver."
Choosing the Right LNA
Once you have your target gain range, our GPS/GNSS Low Noise Amplifiers collection covers GPS L1 through L5, GLONASS, BeiDou, and NAVIC, with filtering built into the amplifier itself for rejection of nearby cellular, LTE, and ISM band interference. If your installation needs to power an antenna over the same coax carrying your RF signal, pair your LNA with our GNSS Filtered Bias Tee, or choose one of our LNA models with an integrated bias tee to handle both in a single part.