Software Defined Radio (SDR)

If you don’t have one of the latest and greatest expensive scanners, you will struggle to listen to a lot of transmissions. While there is still a lot of Analogue transmissions today, even a lot still on AM especially when it comes to Aviation, however most have gone to digital.

There are several reasons for this, but put simply, digital seems to have a longer range, is clearer and you can do a lot more using just the one frequency.

For the hobbyist, to make matters hard, there are many digital modes.  P25, DMR, NXDM are just a few.  Some of these are popular, and some are not.  Then within these digital modes are different ways of using them.  For example, DMR can have T1, T2 or higher, where T stands for Tier.  What this is the radio will do one micro second for T1, then switch to T2 for the next micro second.  Effectively you can have two different conversations on the same frequency, and although every second micro second is lost, to the user you wouldn’t know. This is just one example of DMR.  You can also transmit text messages, your location and so on, all behind the user that is talking and on the one frequency.  So instead of needing to pay for 2 frequencies for two channels, you can have two talk groups on the one frequency.

And this is just the start.  It is clear my old scanner won’t cope with this at all.

However, you can do it all at minimal cost on your PC.  While your PC isn’t as portable as your scanner, it is a lot cheaper alternative and give you an idea on what you can here.

It is a bit fiddly though, and can take a while to setup.  One tick box wrong can silence everything.

Here is what I did, however there are many options, longer than your arm, so do what you think is best for your situation.

When Digital TV came in, a lot of people had trouble receiving it, and additional repeater stations had to be installed along with a lot of home TV antenna’s being upgraded.  So, whatever you do, make sure your antenna isn’t letting you down.  You can try what you have first if you want, but if it doesn’t work, have a think if you need to upgrade your antenna.

I downloaded AirSpy, a program where you can tune in the frequency and add a lot of plugins if you want to.  While this program is rather technical and can be hard for the first-time user, after using it a little while I think it is very well set out.  You can see this program in the picture below where I have the number 1 in red on it. I recommend you download the Community Package with Plugins. If you want some tips on how to get going, I recommend going to this page that has an easy step by step setup guide. Remember, there are so many options regarding this software so try not to get overwhelmed. Just look at what you need to, for example, don’t worry at this stage about tracking aircrafts – a good project for tomorrow!

The next step is to buy a SDR.  This can cost almost as much or as little as you want.  An entry one can cost somewhere between $30 and $50 Australian dollars.  However, I recommend you buy it via the AirSpy store, as there have been some imitations out there.  This is where I got mine from if that helps you. However there are heaps of other options available on this page also. Before it arrives however, you can use the AirSpy software to tap into other shared SDR users that share their devices over the internet.  There may be one close to you.  This post isn’t about this though or the detail of setting all this up, as it will go on for to long.  It is more about what you can do fairly easily.

An example of my interface. 1 = Airspy screen, 2 = wave, 3 = Dos screen, 4 = Decode box, 5 = Talk Groups

Once you get your dongle, plug in your dongle. Do not install any of the software that it came with (if any), and ensure that you wait a few seconds for plug and play to finish attempting to install the dongle (it will either fail or install Windows DVB-T TV drivers). If you’ve already installed the DVB-T drivers that came on the CD bundled with some dongles, uninstall them first. If you got the same dongle as I did, this is what I did to get it going:

In the folder where you extracted the sdrsharp files find the file called zadig.exe. Right click this file and select “Run as administrator”.

In Zadig, go to “Options->List All Devices” and make sure this option is checked. If you are using Windows 10, in some cases you may need to also uncheck “Ignore Hubs or Composite Parents”.

Once running Zidgig, select “Bulk-In, Interface (Interface 0)” from the drop down list. Note on some PCs you may see something like RTL2832UHIDIR or RTL2832U instead of the bulk in interface. This is also a valid selection. Do not select “USB Receiver (Interface 0) or Interface 1” or anything else or you will overwrite that driver! Double check that USB ID shows “0BDA 2838 00” as this indicates that the dongle is selected.

We need to install the WinUSB driver, so also ensure that WinUSB is selected in the box after the arrow next to where it says Driver (this is the default selection). – Note that there has been some confusion for a few people over this step. The goal is to install the WinUSB driver. So to be clear, the box to the left of the arrow shows the currently installed driver, whereas the box to the right of the arrow shows the driver that will be installed in the next step. The first time you open zadig the box on the left will show either ‘None’, or the default DVB-T drivers installed by Windows (RTL2832UUSB), depending on your Windows configuration and version.

Click Replace Driver. On some PC’s you might get a warning that the publisher cannot be verified, but just accept it by clicking on “Install this driver software anyway”. This will install the drivers necessary to run the dongle as a software defined radio. Note that you may need to run zadig.exe again if you move the dongle to another USB port, or want to use two or more dongles together.

Open SDRSharp.exe and set the “Source” drop down box to ‘RTL-SDR (USB)’. This “Source” tab is on the top left. (Note that the first time you do this you may get a smart screen message indicating that Windows has protected your PC, this is a false alarm. Simply click on “more info” and then “run anyway”).

Press the Play button (the right facing triangle). Your RTL-SDR software radio should now be set up and ready to use! If everything has worked you should be able to start tuning to frequencies.

Important! Don’t forget to also adjust the RF gain settings by pressing the Configure button (looks like a cog) up the top next to the Play button. By default the RF gain is set at zero. A gain of zero will probably receive nothing but very strong broadcast FM – increase the gain until you start seeing other signals.

Decode Digital Signals using DSD Plus

So now your on the air, you can take it to the next level now and decode the digital signals you haven’t been able to in the past.

Here’s what you are going to need:

Uncompressed DSDPlus and DSDPlusDLLs. Copy the DLLs into the extracted DSDPlus folder. Now all the DSD Plus files are in the same folder.

Then extract DSD, then copy SDRSharp.DSD.dll into the Sdrsharp folder. Copy the text in the text file and add it to the plugins.xml file in the Sharsharp folder.

Extract VBCable. Find the setup file (use x64 if you have that pc) and run the file as administrator. Then install driver. You will have to reboot afterwards.

Then have a look from 5:58 in the video below and do the following.

After that, open SDR Sharp.

Go to Audio, and for the output, select cable input – this will pump the audio from the SDR to the Virtual cable input.

From DSD interface, select cable imput here. This will mean the audio from the SDR now goes down the Virtual Cable to the DSD software. Select configure in the DSD interface and change the input audio device number to the input of AirSpy and not something else. Once you have done this, test by changing frequency or pressing the stop button, the blue wave box (number 2 in the above picture) should stop.

If you are not sure what numbers to use, the dos screen that opens when you start DSD has the numbers of input and output devices. Make sure you set this correctly else your input will not work, or you output will give you no sound. Once you have set it correctly, press Create Command Line to update.

On the Decoder Options tab, you can leave it at Auto Detect, but if you know what it is, then you can manually select the mode you want. Once you select the mode you want, press Create command line then ok so the settings get updated.

Tune into the correct frequency that has the digital transmission, then enable aux audio output. In DSD Interface, press enable Aux Audio Output.

Once on a digital frequency, press Start DSD. It then opens a dos screen, this will tell you where the audio output will be, eg speakers. Audio input device will be where you selected on DSD plus, which is the virtual cable.

If it all works, you should hear slot 1 in your left speaker, and slot 2 in your right speaker. If not, check you are on a frequency that has a transmission. Then the graph (2 above) is moving (if not your audio to DSD isn’t getting there), then the dos screen should have lots of text running (if not it may not be a digital transmission).

If your still struggling getting this set up, try the following web site: SDR Users Guide.

There are heaps of more information I could post here, but here are some of the plugins I recommend:


Shuttle Plugin

Scanner Frequency – here is a video on this plugin.

DSD Plus – as mentioned above. Here is another video to look at.

Further Reading

Enjoyed that? Please add your comments below or let us know how you went. I hope it was useful. Remember to subscribe so you don’t miss out on our future posts. Here are some other similar articles you may enjoy:

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