From Radio Static to 210 km: What I Learned With an RTL-SDR

I bought an RTL-SDR without really knowing how deep the rabbit hole would go. What started as a small USB dongle and an antenna quickly turned into an introduction to radio frequency, antennas, aircraft tracking, signal processing, propagation, and a lot of experimenting.

This is what I learned while experimenting with my RTL-SDR Blog V3.

Starting With an RTL-SDR

The RTL-SDR is essentially a software-defined radio receiver built around inexpensive hardware. Instead of having a traditional radio dedicated to one particular type of signal, the SDR sends the received RF data to a computer where software can process and decode it.

My setup was based around an RTL-SDR Blog V3 with a dipole antenna. The V3 covers a huge portion of the radio spectrum, making it possible to experiment with everything from FM broadcasts to aircraft communications and ADS-B.

The First Problem: Why Am I Hearing Nothing?

My first experience was basically static.

I tried different modes and frequencies, moved the antenna around, and generally assumed something was wrong with the hardware.

Eventually I found the actual problem. My SDR gain was set to 0. After increasing it, the difference was immediately noticeable. Signals that previously looked almost nonexistent started appearing.

That was probably my first important SDR lesson: before blaming the antenna, dongle, software, or frequency, check the basics.

FM, AM and NFM

I experimented with several demodulation modes, including FM, AM and NFM.

NFM made a particularly noticeable difference when listening to narrowband radio transmissions. I was eventually able to hear a signal around 162.590 MHz, which appeared to be an ambulance or other radio communication.

The audio wasn't particularly clean, but hearing an actual transmission coming through the antenna made the whole experiment click.

The frequency alone isn't enough to determine what a signal is. Bandwidth, modulation, location, propagation, antenna characteristics and the actual transmitter all matter.

Then I Discovered ADS-B

One of the most interesting things I experimented with was ADS-B.

Commercial aircraft transmit ADS-B data around 1090 MHz. These transmissions can contain information such as aircraft position, altitude, speed and identification.

The fascinating part is that you don't need an expensive aviation receiver to receive them. An RTL-SDR combined with a suitable antenna and software can turn a cheap USB dongle into an aircraft tracking receiver.

My Indoor ADS-B Experiment

I initially used the dipole antenna indoors. With the antenna fully extended, I was able to receive aircraft at roughly 19 km.

At first, that seemed surprisingly good.

But then I started thinking about what was limiting the range.

The antenna was indoors.
The antenna height was low.
Buildings and other obstacles were blocking the signal.
1090 MHz signals are strongly affected by line of sight.
The antenna wasn't specifically optimized for an outdoor ADS-B installation.

That led to one of the biggest lessons from the entire experiment: antenna location can matter more than the SDR itself.

Moving the Antenna to the Roof

My house has a relatively clear view compared with the surrounding area, so I started considering what would happen if the antenna was moved to the roof.

The difference was huge.

With a rooftop setup, ADS-B reception can benefit from significantly better line of sight to aircraft. An aircraft flying at several thousand metres altitude can be visible to a receiver hundreds of kilometres away if the geometry and signal conditions are favorable.

210 km

The number that really caught my attention was approximately 210 km.

Going from roughly 19 km indoors to around 210 km with a rooftop setup completely changed how I thought about the system.

The SDR itself hadn't suddenly become 10 times better. The environment had changed.

Antenna height, line of sight, aircraft altitude, antenna efficiency, coaxial cable losses, receiver gain and local RF conditions all contribute to the result.

Why Aircraft Can Be Received So Far Away

ADS-B operates at 1090 MHz, where line-of-sight propagation is particularly important.

An aircraft isn't sitting at ground level. At cruising altitude, it can be several kilometres above the ground. That gives it a huge radio horizon compared with a transmitter located on the ground.

This is why putting an ADS-B antenna on a roof can produce such a dramatic improvement.

Indoor antenna
      ↓
Low height + obstacles
      ↓
Shorter practical reception range


Rooftop antenna
      ↓
Higher antenna + clearer horizon
      ↓
Much greater reception range


Aircraft at altitude
      ↓
Large radio horizon
      ↓
Potentially hundreds of kilometres

ACARS and Aircraft Communications

ADS-B wasn't the only aviation-related experiment.

I also explored ACARS and aircraft communications, which introduced another side of aviation radio and digital signal reception.

This highlighted another important point: different radio systems have completely different requirements. A frequency that works well for one purpose doesn't automatically mean the same antenna and settings will work equally well for another.

Antennas Became the Interesting Part

After getting into SDR, I realized that the USB dongle is only one part of the system.

The antenna is effectively the interface between the radio waves in the environment and the receiver.

I started looking into:

Dipole antennas
Rooftop antennas
1090 MHz ADS-B antennas
Low-noise amplifiers
Coaxial cable losses
Satellite dishes
LNBs
Antenna positioning
Multiple antennas
Signal triangulation

I also looked at whether an old satellite dish and its LNB could be useful for experimenting with RF reception. That opened another rabbit hole into satellite communications and microwave frequencies.

Do I Need an LNA?

I also considered using a wideband low-noise amplifier, particularly for outdoor antenna installations.

An LNA can be useful when the signal arriving at the receiver is weak, especially when there is significant coaxial cable between the antenna and the SDR.

But I also learned that more gain isn't automatically better.

Too much gain can overload the receiver, causing distortion and making signals look worse instead of better.

More gain does not always mean more useful signal.

RF Overload Was Another Lesson

An SDR has a limited dynamic range. If a very strong signal enters the receiver, it can affect the ability to receive weaker signals elsewhere in the spectrum.

This means that a good SDR setup isn't simply about maximizing everything. The goal is to get a clean signal without unnecessarily overloading the front end.

From WebSDR to My Own Receiver

I had used WebSDR before, so I already knew that it was possible to explore radio remotely through the internet.

The RTL-SDR was different because it put the receiving hardware directly in my hands.

Instead of selecting a frequency on somebody else's receiver, I could experiment with my own antenna, my own location, my own gain settings and my own RF environment.

That made the learning experience much more interesting.

What I Learned About RF

The biggest lesson wasn't actually how to operate an RTL-SDR. It was learning how many variables exist between a transmitter and a receiver.

A signal isn't simply "there" or "not there".

Reception depends on things such as:

Frequency
Modulation
Bandwidth
Transmit power
Antenna design
Antenna orientation
Antenna height
Polarization
Line of sight
Terrain and buildings
Coaxial cable losses
Receiver sensitivity
Receiver gain
RF interference
Atmospheric and propagation conditions

The Biggest Takeaway

When I started, I thought the SDR was the interesting part.

Now I think the entire RF chain is what makes the hobby interesting.

Signal
  ↓
Propagation
  ↓
Antenna
  ↓
Coax / LNA
  ↓
SDR
  ↓
Software
  ↓
Decoded information

Changing any one of those components can completely change the result.

What's Next?

The RTL-SDR has already taken me from simply seeing static on a spectrum display to receiving aircraft hundreds of kilometres away.

The next step is going deeper into RF rather than simply collecting more signals.

That means experimenting with better antennas, understanding propagation, learning more about signal modulation and decoding, improving the rooftop setup, and eventually exploring more capable SDR hardware.

I've also started looking at hardware such as the HackRF, which opens up the possibility of experimenting with both receiving and transmitting.

And that's probably the most interesting thing about SDR: a device that initially looks like a cheap USB TV tuner can become an entire laboratory for learning about radio.

Current setup: RTL-SDR Blog V3 + dipole antenna, with experiments ranging from FM and narrowband radio to aviation communications and 1090 MHz ADS-B.

Best reception observed: approximately 210 km for ADS-B with a rooftop setup.

From Radio Static to 210 km: What i learned with an RTL-SDR