SDR (Software Defined Radio) for Under $20

This is a new, inexpensive USB device, is taking amateur radio operators by storm. SDR radio, or Software Defined Radio, has been around for some time now, however, the cost of these SDR’s have kept many from enjoying the technology. Now you can purchase one of these SDR receivers off the internet at websites such as eBay for less than $20

DVB-T Stick

So you’re probably wondering why this thing comes with a remote control. These are actually intended to be a digital terrestrial TV receiver, and use the DVB-T standard (which by the way won’t work here in the states), however that’s not what we’re wanting them for.

You will need to throw out the software and remote because you won’t need it. You will need some software (which is free) that will allow you to use the DVB-T USB stick as a SDR radio. There are several software packages available that will work with the USB stick, however I am going to provide the easiest steps to get your SDR up and running.

The great thing about these is the wide frequency coverage, some models vary. The USB stick I have will cover from 24 – 2300 MHz, and sensitivity when used with a “real” antenna is comparable to a normal radio in your ham shack. Image rejection from strong signals is not the greatest, however later in this article I will talk about how to reduce the effect.

System Requirements

Windows XP**, Vista, 7 & 8*

Intel Pentium 4 (minimum, read my remarks), Core2Duo/Core i3 or higher

1 GB of RAM or better

200 MB of available disk space (for installation), you will need considerable disk space to make recordings (we’ll talk about that further on).

Windows XP is a bugger, you can make these run under Windows XP, however you wont be able to use the software package I recommended most likely (I received a nasty DLL error), there are a few steps to fix but this might be for the more tech savy ham.

Windows 8 I have not tested, but since apparently Windows 8 shares a similar driver model as Windows 7, it is assumed everything should work fine (feedback requested).

Installation of Software

For most folks who want to jump right in, and not through hoops to get this to work can download a software package that includes:

  • RTL2832U Drivers (these make the device work with windows and your SDR application)
  • HDSDR
  • ExtIO
  • USRP Interface
  • BorIP

Now some of this software isn’t needed (such as BorIP), but depending on your usage, it may necessary, and this stuff doesn’t take up that much room.

You can download this package here. All the software is in a ZIP file and you will need to extract the ZIP file to run the setup application.

During the setup you will be asked to setup a device using Zadig. Zadig will setup the USB driver for your SDR. If you don’t see anything that says “Bulk-in, Interface 0” just click on Options and click “Show all devices.”

zadiag

 

Choose the Bulk-in, Interface 0 and click on Install Driver (mine shows replace driver because it is already installed on my computer). Once this is completed you will be given to option to install HDSDR or WinRAD (I suggest HDSDR, but there are others that are available)

Once the setup is complete, you may want to restart the computer to ensure everything works.

Basics of HDSDR

hdsdr1

  • Top – RF waterfall (you can adjust contrast, zoom, and speed)
  • Middle – RF scope
  • Bottom right – Audio spectrum waterfall
  • Audio spectrum scope below waterfall

You will notice that you have two frequencies showing. One is the LO (Local Oscillator) and the other is the frequency you’re tuned to. The easiest way to tune to a frequency is to start typing it in, a box will immediately appear and you will choose kHz or MHz.

Buttons and Keyboard shortcuts

F5 – Soundcard – This allows you to choose and configure your soundcard, most of the time default settings are sufficient. If you have more than one soundcard you may want to change this.

F6 – Bandwidth – This sets the amount of bandwidth that the SDR will use. For SSB, or Narrow FM you may want to use 24000. While wider bandwidth modes such as AM, FM (including FM Stereo) you will want to set to the highest setting of 192,000. NOTE: If you do not see an option for 192k, then your soundcard cannot sample at this rate.

F7 – Options – This is the big one. This menu allows you to fully configure HDSDR. Anything from changing the sample rate, customizing the display and so on. Which bring us to the next section.

F1 – Help/Update – Contains links to help and information about HDSDR

F11 – Full Screen – Toggles back and forth from full screen.

F2 – Start/Stop – Starts and stops the SDR reciever

F3 – Minimize – Minimizes HDSDR to the taskbar

F4 – Exit – Exits the HDSDR application

A couple of tips

In addition to typing in the frequency you want to receive you can tune and fine tune the frequency by placing the cursor over the numeric display using the scroll wheel. You can apply a NB (Noise blanker), as well as IF and RF noise blankers. In CW mode you can set HDSDR to follow the CW signal in addition to other filtering.

CPU Speed and Performance

You will need a fast processor to take advantage of the higher sample rates and wide bandwidth modes. On slower, older computers, you may notice jitter and break-ups in the audio. If this is the case set the SDR to a lower sample rate. Depending on the software package you use, the sample rate can range from 1.0 Msps to 3.2 Msps. When using the Extio_RTL.dll (not used in the setup I’ve outlined) you can set the sample rate as low as .25 Msps. The sample rates translate into MHz of bandwidth, 3.2 Msps is equivalent to 3.2 MHz. This means when set at 3.2 you can look at 3.2 MHz at a time.

Recording and Disk Space

If you decide to record the RF from your SDR you will find that this uses disk space very quickly. Recording our weekly net, which lasts around 30 minutes will use over 20 GB of disk space at the 3.2 Msps sample rate. If disk space is low consider switching to a lower sample rate before recording. The recordings are in a WAV format, however, these WAV files (which are normally just an audio file) can only be played back by HDSDR. You may find that your recordings are broken up into several files, as the file size limits for a WAV file are 2 GB.

Image rejection

Image rejection is that ugly thing where a strong signal appears all over the radio dial. This can be combated by adjusting the gain. Also note that if you are using the extio_rtl.dll file (not used in the above setup) there is an automatic gain control, however adjusting may still be needed in some cases.

Antenna performance

The antenna that comes with your SDR is not very good, in fact you might find that you don’t pick up much other than our local repeater and the couple FM broadcast stations. There are several options here. You can improve the existing antenna by attaching a longer element, using an adapter to use a different antenna, or simply cut the wire and solder a SO239 connector to attach a good antenna. W4GUD, Howard, says that the sensitivity of the SDR is comparable to a regular receiver when a suitable antenna is used.

Upconverters & Other sources

It is possible to get the good stuff below 24 MHz by using an up converter. An upconverter converts HF frequencies to a frequency that the SDR can use. Calibration of HDSDR is required when using the upconverter for HF reception. These upconverters are available at www.nooelec.com

You can also find more information about decoding certain digital modes and use other SDR software to take full advantage of the DVB-T USB stick. KF4QCB, James has provided some links with good stuff, be sure to check them out.

www.rtl-sdr.com
w
ww.rtlsdr.org

 

I encourage everyone to look into these, and remember if you run into trouble we’re here to help, that is what being a ham is all about.