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.
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| Cheap and Easy SDR Box Front |
Cheap and Easy SDR Cutaway view |
Cheap and Easy SDR Box Back |
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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
SDRSharp.exe.Config.ORIGINAL
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
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| RF Gain= -1dB | RF Gain= +9dB | RF Gain= +19dB | RF Gain= +29dB | RF Gain= +42dB |
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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.
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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…
N2YP February 3, 2013 at 2:59 pm
I installed the SDR after the QST article with the same hardware/ software. I am having problem with its receiving. I am only able to receive one local fm broadcast radio station which is less than 10 miles away. If I crank up the gain I can get a few more but the are full of tons of static. I use the same antenna on my 857D and can hear stations 80+ miles away crystal clear. Being in a rural area this makes it useless to receive any land mobile stations. I was wondering how this compares to our experiences and if you had any input. 73 N2YP john@n2yp.com
Dan February 4, 2013 at 7:34 am
John I can’t give you an A/B comparison which I think would be the best. However, I did have the following experience that might help you figure it out. I installed everything per the article and was running happily. I’m using a desktop PC which is in a metal (shielded) box, not a laptop. I’m only using a ~12″ whip sitting on the side of the case which is on edge so about 18″ off the ground. The side of the house is stucco so essentially a Faraday cage thought I’m not sure if the chicken wire is grounded purposely. Anyway after about 4 or 5 days I turned it on and could hear nothing. I noticed though, the noise floor was substantially higher than it had been previously (my photos show ~-60dB) I believe it was about -20dB. I could only hear one or two FM stations and could NOT hear any of the Police/Fire/EMS transmitters.
To get it working again I had to reload ALL software. That may have been more than necessary, but I had tried different parts so after three failed attempts did the wholesale change out. Success! This was why I wrote the article as I realized afterwards I could have saved some time if I had saved a virgin copy of everything before using it. Let me know if it works, good luck!