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Ultra Cheap Software Defined Radio Hack

by admin on April 15, 2014

OK,  so I didn’t invent this idea. It’s been floating around on the web for a couple of years but I finally decided to try it and thought I would share my experiences in turning a $25 Digital TV dongle into a generic RF (radio frequency)  receiver front-end capable of receiving continuously, all-mode from 100-900 Mhz, all might I add, for less than $25. Listen to military radio, police radio, satellite, you name it, albeit with some varying antenna requirements from a piece of wire to a gain antenna. This hack gives you a $5000 tactical radio receiver system (spec-wise) for $25.

Realtec RTL2832 IC in USB Dongle

Software Defined Radio (SDR) is essentially sampling radio frequencies directly just like you would sample audio frequencies for digitization. Using the CD analogy, a stereo signal containing music which is comprised of audio frequencies in the 20-20,000 hertz range is sampled 44.1 thousand times per second. This device directly samples frequencies that start at 100 Mhz and converts to two signals called “I” and “Q” that used to be (and still can be) fed to the L and R microphone input of a sound card. What is cool about this is that when you share this application over the internet, you are sharing not just a single listening port but rather a slice of the radio spectrum. The device converts to a specified center frequency and the sound card provides a 96Khz bandwidth of data. This is important as when you share the application via TCP/IP, you are actually sharing that 96 Khz “chunk” of bandwidth. You can try some of the on-line shared SDR receivers at www.websdr.org. Direct sampling and subsequent demodulation provides an exceptionally high signal-to-noise-ratio (SNR), which would have only been possible in the analog realm with extensive circuitry. This entire circuit is primarily one ASIC (Application Specific Integrated Circuit), the Realtec 2832 IC.

What is remarkable about Software Defined Radio is that the technology responsible for the ability to sample high frequency (HF) , Very High Frequencies (VHF), and Ultra High Frequency (UHF) RF is that Application Specific Integrated Circuit (ASIC) Technology has made it possible for exceptional fast processors using technology that wasn’t readily available on a non-commercial basis a decade ago. Indeed we have gone from a $10K box to a $400 box to a device in a dongle that can be purchased off of Amazon for less than $25. This dongle is really designed to allow you to plug into your laptop and tune digital TV channels which run from around 100 Mhz up to 900 Mhz.

This hack does a couple of things – first it substitutes a driver for Windows to recognize the Realtek 2832U IC . then uses an open source software called SDR# to provide a user interface (UI) for changing frequencies and filters. The interesting thing from a radio perspective of receiving in this manner is that no frequency is off-limits, however the demodulation (that is,  the process of converting the superimposed audio over the radio carrier back to audio that you can listen to) is limited to AM, FM, narrow-band FM (police radio), SSB and CW. The waterfall display makes it easy to spot subtle amplitude shifts over a broad frequency spectrum. (this is one of the reasons that “waterfall” displays are used in both medical and military ultrasound).

I struggled for over a year trying to get this to work in Windows. I understand that some people had better success early on running on Linux of some flavor, but but my first experience with Ubuntu was not positive. 
So here’s what I did to make it work:

  1. Download and install Zadig USB driver replacement utility. Zadig replaces the goofy DTV driver with a universal Windows driver. You can download and follow the instructions here.
  2. Install SDR# from the website here.
  3. You should be able to go to Windows Control Panel and see the 2832 device under Universal Serial Bus Device (this means that Zadig did it’s job)

control panel

 

Launch SDR# by double clicking on SDR. You can also save this .exe on your Start Menu or toolbar…

sdrexe

 RESOURCES:

  1. RTL-SDR.com – for more on the subject
  2. Add HF module for 0-30 Mhz (shortwave) coverage. Some assembly required. YouTube Video
  3. Listen to SDR radios on the web from various locations

 

                    

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2 UHF Grounded Element Yagi Antennas

by admin on November 7, 2013

UHF Commercial Yagi Antennas

I wanted to experiment with the so-called “Plumbers Delight” Yagi-Uda antennas – that is,  directional antennae whose driven, active element is at the same potential as the boom so it’s welded together- which apparently delights plumbers, as they are so-named “plumbers delight”. This allows the element to be welded to the boom, making them very durable. The other advantages of neutral-potential Yagis are very low noise floor and relative lightning immunity as they can take a direct strike as they are at ground potential.

The unusual element-to-boom potential required some nuanced feed impedances however. Originally I was going to implement a Gamma Match which basically adds capacitive reactance to the antenna.

This time I used a balanced Delta feed with integral 4:1 coax balun. Thus I can achieve a 52 ohm match with less than a 1.2:1 SWR at 449 Mhz. My next project is a an X-Y 144/444 Twist Yagi for AMSAT operation. They  also make the perfect ant for terrestrial data capture systems with a UHF satellite data uplink data-radio.

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Super rack mount computer project

January 30, 2013

  Build a $3000 computer for under $700 and win all of the computer pissing contests While my former computer was only a year old or so, it was in a big gamers case with room for 10 hard drives,  (I only used 3), and took up an inordinate amount of space.  Also it was […]

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Schumann Resonance and the fifth dimension

August 25, 2012

Before you think that this is about a musical conflagration involving 70’s pop and classical compositions – stop right there… If you’re like me though, you would probably be intrigued as I was when I encountered a couple of really weird pieces of physical (as in physics) trivia and started thinking about what else do […]

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Latest Repeater Project Pic

June 4, 2012

The saga of the never ending repeater project… This is the Voice-over IP UHF radio repeater system that Tim Hardy and I have been working on for over a year.  It’s is a custom made radio repeater system that uses open source Asterisk voice-over-IP (VoIP) to allow the radio system to be remotely accessed via […]

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The Google Security Question

April 16, 2012

We all know that Google has had unfettered access to virtually all of our data. Google has long since had one of the most non-commercial search engines, allowing you to search for, say, “sodium” without being bombarded with ads for on-line merchants selling salt shakers. We’re all familiar with the Google “Street View” that allows us […]

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3D Polymer Printing

December 29, 2011
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The Story of Hedy Lamarr and Frequency Agile Transmission

December 3, 2011

National Public Radio recently did a piece on Richard Rhode’s new book entitled “Hedy’s Folly’s” that documents Hedy Lamar’s contribution to modern technology. Most do not know the story of Hedy Lamarr, who aside from being a movie starlet and being called “the most beautiful woman in the world”, also invented the concept of “frequency […]

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Cisco’s Little “Flip” Pocket HD Video Recorder

October 26, 2011
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I first heard about Cisco’s little Flip pocket HD video recorder at a communications conference a few months ago. A PR director had extolled the attributes of Cisco’s tiny little under-$100 video recorder. It was touted as a nice alternative to recording video with your camera which chews through your SD card memory faster than […]

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