SDR (Software Defined Radio) - DONE.LAND

Traditional receivers are designed to tune into a specific frequency, meaning you can only monitor one frequency at a time. To listen to a different frequency, you must manually adjust the receiver.

SDR (Software Defined Radio) receivers, however, work differently. They capture a wide frequency range, and modern signal analysis software running on a computer can visualize all the signals within that range simultaneously.

This approach is highly beneficial for analyzing and debugging RF (Radio Frequency) devices. You no longer need to know the exact frequency a device is using. For example, if you suspect that a device is operating at the wrong frequency, you can tune your SDR to the approximate range and immediately see the actual frequency in use.

SDR is a broad field, and many HAM radio enthusiasts use SDR receivers to listen to radio stations worldwide. SDR receivers come in various quality levels and price ranges. For lab use, however, a simple SDR USB stick priced around €20 is often sufficient.

Overview

Radio waves are invisible, so special tools are required to visualize them in order to analyze and troubleshoot RF components.

For instance, if you’re having trouble connecting two RF boards, it helps to verify that both components are indeed using the same radio frequency and modulation.

Moreover, radio frequencies are regulated, with many restrictions in place. To ensure you stay within legal limits and avoid interfering with other services, you may need to measure the actual RF power your devices emit and check for unwanted spurious emissions.

Lastly, if you’re looking to optimize your wireless transmissions, you’ll want to assess your antennas. Are they performing as expected? Are they properly tuned for the frequencies you’re using?

SDR Receivers

SDR receivers are relatively simple circuits because most of the heavy lifting is offloaded to a computer. The computer’s processor handles the complex signal analysis and visualizes the signals present across the chosen frequency range.

This is why it’s possible to start with a basic and inexpensive SDR receiver. However, the computer itself needs to be powerful enough to process large amounts of data.

The quality and frequency range of the SDR receiver determine how much raw data it sends to the computer. For smooth operation, you need a fast USB connection (at least USB 2.0, but ideally USB 3.0) along with high-quality USB cables.

Software

In SDR, software plays a central role.

Most SDR software is open-source and free for personal use. These applications are generally of very high quality, but as with many free tools, they may have limitations. For instance, some software may only be available on certain operating systems, depending on the preferences of the software’s creator.

Therefore, when choosing SDR software, pick one that works well with your preferred operating system. Most SDR software supports the same core functionality.

In this guide, we will use SDR Console, which runs on Windows PCs. It is sometimes referred to as sdr-radio.

SDR Radio Devices

A wide variety of SDR radio devices are available. These range from affordable USB dongles to high-end, professional models that can cost hundreds or even thousands of dollars. Many popular models are also available as cloned devices, which may work just as well, or may not work at all.

Choosing a brand-name SDR radio is important because hardware drivers can be the most challenging part of installation. Brand-name products typically come with quick start guides that provide helpful information and links to necessary drivers.

Clones and unbranded devices often lack adequate support and documentation, which means you may encounter difficulties getting them to work, no matter how inexpensive they are.

SDR Console (Software) Installation

SDR Console is a well-regarded SDR software, but it is only available for Windows PCs.

Downloading

Downloading SDR Console can be a bit challenging (as of this writing). The website is overloaded and confusing, requiring several clicks to access the download link on OneDrive or Dropbox, where the software is hosted.

Follow these steps to download the software:

Navigate to sdr-radio.com. Scroll down a bit on the Home page until you see the button Download SDR Console. Alternatively, you can directly visit this link to proceed directly to the download section.
On the download page, in the upper section, click Release:
This will scroll you down to the actual download options:
Clicking DOWNLOAD will not take you to the download immediately. Instead, click on either the 32-Bit or 64-Bit version listed, for example, to download the 64-bit version from Microsoft OneDrive.
This will lead you to the actual download page. From there, click Download to begin the download process.

Installation

SDR Console is not a portable app and requires installation.

Run the downloaded executable file. You will be prompted to provide Administrator privileges. Click Yes to proceed.
The installer unpacks the necessary files. This process should only take a few seconds.
The actual installation process begins. Click Next and follow the on-screen instructions.
The installer will confirm the installation directory, which defaults to your primary hard drive. If space is limited, you can select a different drive.
During installation, any missing components (e.g., C++ redistributables) will be installed. Each component will launch a separate installer, so be sure to click OK when prompted.
Once the installation is complete, click Next, check the box to Start the program now, and click Finish.

This will close the installer and launch SDR Console. The program’s red round icon with an antenna will appear in your taskbar.

Be sure to right-click this icon and choose Pin to taskbar for easy access in the future.

Adding an SDR Radio Device (Hardware)

For SDR Console to work, it needs at least one physical SDR Radio Receiver. On the first launch of the software, a dialog box will prompt you to add your SDR receiver.

Follow these steps to add your SDR receiver:

Plug in your SDR receiver, so the software can detect it.
In the dialog box that opens, click Search. A drop-down menu will appear. Select your SDR device (e.g., RTL Dongle/USB). SDR Console will search for your device.
Once the device is detected, click Add. The software will automatically populate the technical details of your device, and it will appear in the list of available devices.
Don’t forget to click Save to keep the device in your list. From now on, you can simply double-click it to select it whenever you launch SDR Console.

You can also add additional SDR devices if desired.

Hardware Not Detected

If SDR Console fails to detect your SDR receiver, and you’ve confirmed that it’s connected and the correct model was selected in the Search menu, the issue might be related to USB device discovery.

Here’s how to fix it on a Windows PC:

Plug your SDR stick into a USB-A port. You should hear the sound indicating that a new device was recognized. Press WIN+R and type devmgmt.msc to open the Device Manager.
In Device Manager, check for any unknown devices or devices with strange names such as Other devices/Bulk-In. If you see one, the SDR device may have a USB driver issue.
Install Zadig, launch it, and select the unknown device from the drop-down list (e.g., Bulk-In, Interface 0).
In the Driver field, check whether a driver is installed. If no driver is present, select WinUSB from the drop-down menu and click Install Driver. This process may take up to a minute.

After installing the correct USB driver, return to SDR Console and try searching for your SDR device again. It should be detected within a few seconds.

SDR Console - First Steps

Once you have installed SDR Console and added your SDR Radio Device to it, let’s walk through the first steps:

Launch SDR Console
If you pinned SDR Console to your taskbar, click its icon. Otherwise, navigate to the installation folder and find SDR Console.exe. Launch it.
Select Radio
A Select Radio dialog will open, listing all SDR receivers you’ve previously added. Select the one you want to use.
Set Bandwidth
In the lower part of the dialog, you can select the bandwidth. This refers to the frequency range that can be monitored simultaneously in the spectrum. The available bandwidths depend on your SDR receiver’s quality and performance. A higher bandwidth requires more computational power and higher data transfer rates. Start with a low bandwidth, such as 1 MHz, then click Start.
Start Listening
After a few seconds, SDR Console will start emitting sound, most likely static. By default, it will tune to 7.1 MHz.

Listening to Public Broadcast

Now, let’s tune into the radio frequency range and modulation type you want to examine. As a first test, tune into VHF public broadcast:

Set Frequency
Click on the frequency meter in the upper left corner. On each digit, there is a square above and below when you hover the mouse over it. Clicking the square increases/decreases the digit. Tune in your favorite VHF radio station, or tune in a frequency in the range of 88-108 MHz.
Spectrum and Waterfall
The spectrum display will now show any signals that can be picked up in the selected bandwidth around the frequency you set. So if you dialed in 100.000.000 MHz (100 MHz), and defined a 1 MHz bandwidth when launching the software, the spectrum will show all signals in the range 99.5-100.5 MHz.

Even if you don’t know a particular station’s frequency, you can discover signals within the monitored spectrum. Simply click on a signal in the spectrum to tune to it.
Modulation
To actually hear the public broadcast transmission, you need to set the modulation type to the appropriate one.

On the left side, click Mode, and from the drop-down, select W-FM (wideband FM). Done! Now, if you’ve tuned into a radio station and cranked up the volume, you should be able to hear music or news.

Testing RF Remote Controls

Now let’s try something more practical: You may have found an old RF remote control and want to figure out which frequency it uses.

Tune to Suspected Frequency
Set SDR Console to the first suspected frequency range, such as 433.920.000 (433.92 MHz).
Listen for Signals
Listen for a while. You may pick up various ISM band transmissions, from short bursts from remote controls to regular intervals from digital data transmissions. The waterfall display shows signals over time. If the transmission is on a license-free band, the signals should be centered around 433.92 MHz.
Test the Remote Control
Press the unknown remote control and check whether it emits a signal in this spectrum. It should produce a much stronger signal, as it is much closer to the receiver.

Findings

Your remote control may be within the monitored range, but its transmission frequency might be slightly off.

The weak signals in the middle of the waterfall come from unknown sources at precisely the center frequency 433.92 MHz, while the tested remote control transmits around 433.78 MHz.

The default waterfall speed is 40 lines per second. To adjust the speed, go to View > Speed. With the vertical bar on the right side, you can set the sensitivity. Click Auto on top to auto-tune the waterfall to the best sensitivity.

You found that your remote control:

Works
Uses the 433 MHz frequency range
Is slightly off (±150 kHz is typical for inexpensive RF remote controls)

If your remote control didn’t produce signals within the monitored spectrum, try switching to other common frequency ranges, such as 315.0 MHz, and test again.

Conclusions

The example test cases illustrate the value of SDR bandwidth: if an SDR receiver were capable of i.e. 200 MHz bandwidth, it could monitor the full frequency range from, e.g., 300-500 MHz, picking up remote controls from both ISM bands in one sweep.

However, such bandwidths are beyond the reach of most affordable SDR receivers:

SDR Model	Max Bandwidth (MHz)
RTL-SDR (RTL2832U)	~2.4 (practical ~2.0)
HackRF One	20
LimeSDR Mini	30
LimeSDR USB	61.44
USRP B200	56
USRP B210	61.44
Airspy R2	10
Airspy Mini	6
SDRplay RSPdx	10

With these SDR models, you need to manually switch frequency range once signals fall outside the monitored bandwidth. That’s perfectly acceptable, and even a 2 MHz bandwidth often is overkill for typical RF test scenarios.

High-performance SDR receivers, however, can easily achieve broad monitoring:

SDR Model	Max Bandwidth (MHz)
Ettus USRP X310	160
Ettus USRP N320/N321	200
Ettus USRP N210	25
Per Vices Cyan	1,600
Per Vices Crimson TNG	960
Per Vices Chestnut	500
NI/Ettus USRP X410	400
Analog Devices AD9361	56
Analog Devices AD9371	100
FlexRadio 6700	14 (per receiver, 7 receivers)
RFSpace NetSDR	1.6
Signal Hound SM200B	160
R&S PR100	10
R&S EB500	20

Regulators also use SDR technology, albeit a bit more powerful (more similar to this). That enables easy monitoring and detecting of suspicious RF signals that should not be present in unauthorized frequency ranges.

Another reason why these days you should definitely adhere to legal regulations, and not transmit on frequencies outside legal ranges or with excessive RF power.

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