Radio Hackers: Preamplifiers & LNA

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21 Oct 2025

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If you’re new to the radio scene, it can often be difficult to cut through the noise and figure out what you need. And, while there are now great package deals available to give you antennas, receivers and preamps in the one kit, you’ll still need to figure out the basics regarding how everything all works.

It’s often said that amateur radio is 90% listening and 10% transmitting, and if your only receiver is a receive-only RTL-SDR then this becomes more true. But for many, the focus is on the antenna, yet beyond that, the LNA becomes an important part of helping to optimise your station correctly.

Let’s take a look at the role they play, the different types we might find and the sorts of signals that they tend to work best with.

What Is A Preamp

Preamps are used to increase or boost a signal before it arrives at the receiver's front end. Working best on marginal signals like satellites or weaker receivers, for some of these signals, preamps are an essential part of the entry barrier. While it’s not as noticeable when working in the VHF/UHF frequency range, by the time you hit microwaves at 1GHZ and beyond, a preamp becomes an essential part of your receive station.

They come in both internal and external variants, with some receivers having onboard preamplifiers built into the design. Typically, they’ll require some form of power to run properly, and while you can purchase units with onboard batteries, the RTL-SDR blog dongle and high-end SDR units will have an onboard bias-T that enables power to be sent up the feedline. This makes the installation and addition of a preamp much easier.

Why Are They Important?

When evaluating the sensitivity of a receiver, one of the areas of focus is the “noise floor”. And while RTL-SDR dongles are great pieces of hardware for the price point, they do tend to suffer from a higher noise floor. This won’t preclude you from detecting strong signals, but if your interest is space communications or other weak signal work, this will often pose a problem.

Using a preamp can help to bring this signal up “out of the noise”, often making the difference between a successful contact or reception in comparison to missing it entirely. Correctly configured and installed, a preamp should bring the signal-to-noise ratio up, without degrading the signal quality.

It’s important to point out that you can’t miss what you can’t hear. So, if you haven’t given some thought to adding an LNA to your system, it’s worth considering. It might just open up a whole new door.

It’s All About Placement

With most systems, the bulk of signal loss occurs in the feedlines between the transmitter and the antenna. This is even more prevalent in frequencies above 1Ghz. While you can place your preamp at any point in the system, you’ll find the best results come from positioning it close to the antenna where the signal is strongest.

In the older amateur radio days, this would mean a bias-t followed by a run of (usually expensive) low-loss coaxial cable to the receiver. In 2025, though, small electronics and IOT devices are now the name of the game. So, depending on your station, you can use a USB cable to access it, send it over the internet via rtl_tcp or even put a Raspberry Pi at the antenna and access the whole thing wirelessly. I mean, you are an aspiring radio hacker after all, right?

A Word About Noise

Preamps are a great tool, but it's worth pointing out that, like most things in the world, they do come with some limitations that you ought to be aware of. The biggest issue is that often, preamps can amplify any noise, not just the intended signal you’re looking for. If you’re in a marginal noise area, then you probably aren’t going to have a problem with this, but those in cities or near large transmitter towers may find these to prove problematic.

This won’t preclude the usage of an LNA or preamp, but it may complicate it slightly. In this instance, filters are your friend, helping to mute this excess noise entirely. While units like the SDRplay have built-in filters, for devices like the RTL-SDR, this typically means purchasing hardware units to add in-line.

The other thing to be cautious of is the varying build quality of the different types of preamps on the market. While some are of acceptable quality, others are outright junk. So, if you’re looking to purchase your first LNA, it’s worth keeping this in mind. Purchasing a quality unit helps ensure your first experience with the hardware remains a positive one.

It’s In The Numbers

Given the sheer number of systems currently available to purchase, it can be tough to give a blanket assessment of what to expect when assessing a preamp, but to help get some context, we can use the numbers from the ever-popular Sawbird LNA system.

A single-band LNA with onboard filtering to help optimise the reception of space-based weather satellites, the system adds just .7db of noise to the noise floor and provides a whopping 20db of gain while rejecting or attenuating out-of-band signals.

The proof of the pudding is the design, though and putting it in the field for testing proves the strength of the design. With no preamp and a HackRF, Meteor M2 signals would disappear into the noise at around 15 degrees of elevation using a home-made QFH antenna.

Adding the preamp inline at the antenna and being blessed with good elevation overall meant that with no other changes, the same satellites could easily be captured from horizon to horizon.

Go Try It Out

If you’re new, radio is often confusing but in the VHF & UHS bands RF is often pretty tolerant of mistakes, particularly in receive-only systems. More than a few ham radio operators of the earlier generation made their first RF contact using a piece of coaxial cable shoved into the transmitter's centre pin to feed a balanced antenna.

Make no mistake, to focus on microwaves and other high-end systems, you’ll need to have a great focus on build quality and system design. But if you’re out there with your first SDR unit, try to forget about it and ignore the noise. At this level, radio is supposed to be fun and engaging. Worry about the serious stuff later, for now? Just get out and make (or receive) some noise.

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