Cheap and Easy SDR, Let’s do this!
The Cheap and Easy SDR (Software Defined Radio ) article that appeared in January 2013 QST caught my eye. Robert Nickels does a great job describing the project and it is an easy read. The basic premise of the article is to use a DVB-T (digital video broadcast – Terrestrial) “dongle” as the basis for a SDR. You simply plug it into a USB port on a computer (Windows or Linux) after loading some open-source software and you’re off and running.
Cheap and Easy SDR, Buy it!
I purchased my hardware on e-bay for less than $20 including shipping:
The device I purchased is manufactured by Terratec and was advertised as “DVB-T USB Dongle Realtek RTL2832U Elonics E4000 50-2200MH(z)” it included an antenna with a magnetic base, a suction cup adapter for the magnetic mount, and an extension cable for the USB port so that you can move the receiver a few inches away from and change the orientation relative to the PC, for noise reduction if required. The E4000 is the tuner and the RTL2832 is the ADC/IQ decoder.
|Cheap and Easy SDR
|Cheap and Easy SDR
|Cheap and Easy SDR
Cheap and Easy SDR, Install it!
Installation is fairly straight forward here a couple of recommendations for your Cheap and Easy SDR so that if something “breaks” you can get running again quickly.
- Save all of the zip files into a convenient and safe location. ( I created a SDR folder that I stick everything into) I created two icons on my desktop one that starts the receiver (SDR#, SDR Sharp) and another to take me to the folder without starting SDR# (SDR sharp).
- You can download and configure all the software except the dongle driver before it arrives. You need to edit a file so go ahead and do all of that while you’re waiting for your stick or SDR dongle to arrive.
- After you create the config file as described in the QST article, create a copy and save it in a safe place. I made mine
and saved it is in the same directory as all of the Cheap and Easy SDR (SDR#) files.
- The driver installation program requires 7-Zip to unpack. I’m not sure if newer versions of WinZip will decode it (I’m at 11.2), I had to download 7zip. You can’t install the driver until you have the stick as the installation software needs to “see” the stick to install the driver.
- After installing, I took screen shots of the FM broadcast spectrum at various RF Gain settings see below. You can see how the “floor” moves up as the gain is increased. Not surprisingly, when the gain is increased by 10dB the floor goes up 10!
- Calibrate the frequency… I adjusted the PPM offset until the cursor aligned with a known frequency. (I used local police channels) I also used my 440MHz transceiver. I first checked it against a frequency counter then made the display show the same frequency. Photo shows a busy night in San Jose. Can you see all 8 Channels? The picture on the right is a close up of a data channel.
- Run the RTL_TEST.exe program several times to see how your unit behaves. See sample output below. It will tell you in order:
- Any devices & the channel they’re on below indicates Terratec T Stick Plus on channel 0
- It then indicates the tuner type is an Elonics E4000
- The available gain settings, both the number and increments (these should correspond to the ones you see in the SDR# configuration screen)
- It will then summarize the frequency coverage
- Low, High then the L-band hole
|RF Gain= -1dB||RF Gain= +9dB||RF Gain= +19dB||RF Gain= +29dB||RF Gain= +42dB|
In the second picture you can see that the numbers fluctuate around a bit and is the reason I recommend doing the test several times. I performed those two tests as close together as I could.
Like most command line programs the required options are input immediately after the command itself. To test the dongle the complete command is “rtl_test –t” if you send rtl_test –h it will “puke” on you but will then tell you what the acceptable options are.
One thing I’ve noticed with the SDR# software is that it doesn’t “bow out gracefully” What I mean by that is if you are performing the FFT at 4096 samples, and it is “happy” as you increase the sample rate to 8096 and upwards the number of calculation increases. You will notice the computer getting slower and “catching” or “dragging” if you go too high you will have to patiently wait to move the cursor and select a lower value or exit the program and start over at a lower sample rate. It won’t tell you that it can’t do the calculations it will try it’s best, to the potential detriment of your system. If you can’t get out of it, reboot! This makes for an easy entrance into the realm of Software Defined Radios. Good luck with your Cheap and Easy SDR.
I purchased the kit that was offered in the article and will put that together in the near future. Another Day, Another post…