A low noise amplifier (LNA) is an electronic device that boosts a weak radio signal while adding as little extra noise as possible, so the signal stays usable once it reaches a receiver. LNAs sit at the very front of a receive chain, right after the antenna, because that's the point where a signal is at its weakest and most vulnerable to being lost in noise.
Why LNAs matter
Every signal path loses strength before it ever reaches your receiver. Coaxial cable, connectors, and long antenna runs all introduce loss, and that lost signal can't be recovered later in the chain, no matter how good your receiver is. An LNA placed close to the antenna offsets that loss by amplifying the signal before it has a chance to sink below the noise floor.
A typical receive chain looks like this:
Antenna → Feedline (loss) → LNA (gain) → Coax to receiver → Receiver
Placing the LNA as close to the antenna as possible, before the losses of a long cable run, is what makes the difference between a clean signal and a noisy one. This is also why remote-mount and bias-tee-powered LNAs exist: they let you put the amplifier physically at the antenna, rather than back at the receiver where it's too late to help.
The three specs that define an LNA
Gain
Gain measures how much an LNA boosts the incoming signal, expressed in decibels (dB). Typical LNA gain values range from about 10 to 40 dB. As a rule of thumb, every 3 dB of gain roughly doubles the signal power reaching your receiver.
Gain isn't just "more is better," though. An LNA's gain needs to be matched to your system's total loss budget: enough to offset your cable and connector losses, but not so much that it overdrives your receiver's front end (see "Can an LNA have too much gain?" below).
Noise figure
Noise figure (NF) measures how much additional noise the amplifier itself introduces, in dB. A perfect, noiseless amplifier would have a noise figure of 0 dB; real devices typically range from about 0.5 dB (excellent) to 3+ dB (mediocre) depending on design and frequency.
Noise figure matters more than almost any other spec for weak-signal work, because it's the first amplifier in the chain that sets the noise floor for everything downstream. A high-noise-figure LNA can't be fixed by good components later in the receive chain.
In the picture below, the LNA amplifies both the signal and noise present at its input equally. In addition, the output includes noise due to the LNA. This in turn reduces the signal-to-noise ratio. A good LNA contributes very little noise to the overall picture.
Linearity
Linearity describes how faithfully an LNA amplifies a signal without distorting it. A linear amplifier's output power is simply the input power plus its gain, in dB. Push an LNA too hard, or feed it a signal that's too strong, and it stops behaving linearly. It compresses, distorts, and can generate spurious signals that weren't in the original input at all.
In the picture below, the LNA is operating linearly when the signal present at its input has an amplitude of -60 dBm. However, as the input signal is increased to 0 dBm, the device is no longer linear, the output signal is distorted, the gain is no longer 20 dB and the output signal amplitude is only +5 dBm.
Filtered vs. unfiltered LNAs
A plain LNA amplifies everything across its operating frequency range, including signals you don't want. If your receiver has no other filtering ahead of it, strong out-of-band signals (cellular, FM broadcast, other ISM traffic) get amplified right along with your target signal, and can saturate the receiver.
This is why GPIO Labs builds filtered LNAs for specific bands like GPS/GNSS, ADS-B, and 433 MHz: the built-in filter rejects out-of-band interference before it reaches the amplifier stage, so you get the gain you need without also amplifying the noise you don't.
Where LNAs are used
- Software-defined radio (SDR) — compensating for the noise figure of low-cost SDR front ends
- GPS/GNSS reception — recovering satellite signals that arrive at the ground extremely weak
- ADS-B and aircraft tracking — extending range for weak, distant aircraft transponder signals
- Amateur radio and radio astronomy — pulling faint signals out of the noise floor, including hydrogen-line work
- Any long antenna run — offsetting cable loss between a remote antenna and an indoor receiver
Frequently asked questions
What does LNA gain mean in practical terms? It's how many dB the signal is boosted by. If your antenna feedline loses 6 dB over its run, a 20 dB gain LNA placed at the antenna more than makes up for that loss before it happens, rather than trying to recover a signal that's already too weak.
What's a good noise figure for an LNA? For weak-signal applications like GPS or radio astronomy, look for noise figures under 1 dB. For general-purpose use, 1–3 dB is common and often sufficient.
Can an LNA have too much gain? Yes. A high-gain LNA can oversaturate a sensitive receiver, especially in strong-signal environments, producing distortion rather than a cleaner signal. If you're seeing garbled output after adding an LNA, too much gain (or lack of front-end filtering) is a common cause.
Where should I place an LNA in my system? As close to the antenna as practically possible. For the full walkthrough on connecting one correctly, including receiver, transmitter, and transceiver setups, see How to use a Low Noise Amplifier.
Looking for an LNA for your application? Browse our low noise amplifiers, including filtered LNAs built for specific bands like GPS/GNSS, ADS-B, and 433 MHz.