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HDTV via GNU Radio
NortonDC writes "High Definition TV has been successfully captured in its native data stream from an over the air broadcast by a software defined radio that is Free and open source from the GNU Software Defined Radio project."
Seems really neat, but I found that card on a science site. ONLY 1000 pounds (Great Britan). I suspect that this isn't much cheaper in the US either ;-(
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https://directory.adeptscience.co.uk/controller
You can get many TV shows you might have missed by using BitTorrent .
This site has a list of links to various sites which contain TV shows available through BitTorrent.
A West Wing episode is available here (The West Wing - s04e16 - California 47th [ftv].mpg.torrent) (but you need to have installed BitTorrent prior to clicking on that link).
I don't follow West Wing so I don't know whether that's from second season, and your comment is accurate -- that's the only one available from that site. One other is The.West.Wing.S04E14.Inauguration.Day.Part.I .
Enjoy!
I feel fantastic, and I'm still alive.
At $1,299.00 for the PCI card that their driver is written for, I do not see this in my future. For that matter, I don't see that in the future of many hobbiests which makes this project rather useless to the general population at present.
See here for information on the product the GNU Radio project wrote the driver for: Measurement Computing
Maybe some day...
My understanding is that it is a fight against copy protection. Open (Free) software defined radio means that the user can pull down any (unencrypted) broadcast and save it - whether or not the "broadcast flag" (no-copy bit) has been used. In a future in which hardware televisions can't save copies of anything, this will allow the user to save copies and play back later (or do anything else) on a future PC or TiVo. Good stuff.
sulli
RTFJ.
It's not so much a special radio card as it is just any wide-banded data acquisition board and a little frequency-translation unit.
There is a "tuner" that multiplies the incoming radio signals by a variable frequency. When you mix two oscillating signals (by multiplication) you get harmonics. If the variable frequency is just a sine wave (i.e., not modulated with any information), then the harmonics are identical in modulation to the original, but at a difference frequency. The tuning box is used to bring various radio signals down to a frequency that can be digitized by any ordinary data acquisition board.
These data acquisition boards are designed to basically sample voltages of whatever is tied to their inputs, and to sample it very very quickly and very often. Since these boards (and computers also) are getting more advanced (i.e. faster), they are able to sample real radio frequencies (stuff in the ones of MHz ranges).
After you get the signal digitized, it's just a simple matter of writing software that mathematically performs the functions that all the circuitry in the 'old-fashioned' receivers would do with their capacitors, resistors, and inductors (and more).
That's pretty much how it works.
a little expensive for my taste.
Always going forward, 'cause we can't find reverse.
GNU Radio is a collection of software that when combined with minimal hardware, allows the construction of radios where the actual waveforms transmitted and received are defined by software. What this means is that it turns the digital modulation schemes used in today's high performance wireless devices into software problems.
Read the site! This is very important stuff and could have a huge impact on technology.Try one of the GNU mirrors:
e s/hdtv-samples.html
s amples.html
e s/hdtv-samples.html
a ges/hdtv-samples.html
: www.gnu.org/server/list-mirrors.html+gnu.org+mirro rs&hl=en&ie=UTF-8
http://gnu.sunsite.utk.edu/software/gnuradio/imag
http://gnu.wwc.edu/software/gnuradio/images/hdtv-
http://gnu.mscnetworks.com/software/gnuradio/imag
http://www.phildowd.com:4060/software/gnuradio/im
Basically, append software/gnuradio/images/hdtv-samples.html to any of the links from here: http://216.239.57.100/search?q=cache:1KyAbWv9nRAC
Withdrawal before climax is very ineffective and those who try this are usually called "parents."
It could be used for that (assuming you have a way to rebroadcast the signal later? Without the FCC hunting your signal down?), but the purpose of the software is to provide signal-processing software targeted at radio signal processing. If that signal is an HDTV signal, than so be it, but it could just as easily be X-Ray signals from space (assuming your sampling device could capture them) or some AM Radio talk show.
If you look at the site you can see a number of other examples. Since you are no longer limited by a standard radio's hardware, you can do completely different stuff like receive two different frequencies at the same time.
If I have been able to see further than others, it is because I bought a pair of binoculars.
Well, I DO do this stuff for a living, as well as being a computer geek and a ham.
But really, $1300 for the digitizer card is a bit steep - I work with a system using a 40 MSamp/sec 12 bit flash converter and Intersil 50214. The Intersil is about $30, and I don't think the flash converter is much more. Add a $50 FPGA to do the interfacing to the PCI bus, and you could do scatter-gather busmastering capture to the main system pretty easily.
Use a $50 Intersil 50216, and you could do most of the heavy lifting with it - Final IF filtering, I/Q recovery, post-detection filtering, symbol tracking, etc. That would remove a lot of the CPU load from the system, possibly allowing for real-time aquisition and decode.
Go to one of the board fab houses, and you could probably get a board built for about $500, maybe less.
Considering that people are spending $500 for video cards, this might not be so bad.
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This has been covered here on Slashdot before. Some of the comments in the previous post are particularily informative.
Always value the individual over the system. --Bruce Lee "I don't need a Sig - I have a custom 191" - me
A few nitpicks:
.7 volts a 6 or a 5?), and you have to slice at the correct time (the symbols are only defined at certain times - any other time the signal isn't valid, it is a blend of the current and the (next|previous) symbol - what is called inter-symbol interference or ISI). So you have to do symbol tracking - figuring out when to sample, and at what levels to slice.
You don't get harmonics (frequencies that are related to the fundimental by an integer multiple), you get mixing products, also known as "sum and difference".
You get harmonics when you feed a single signal into a non-linear element - feed f1 in, get f1, 2*f1, 3*f1, 4*f1,... out. This is commonly used in tranmsitters to allow the use of a lower-frequency crystal to generate higher frequency carriers - you use a 10 MHz crystal, and the feed it into a non-linear element such as a squaring amp, and pick off the tenth harmonic to get 100 MHz.
Mixing involves feeding 2 signals f1 and f2 into a multiplier - you get f1, f2, f1-f2, and f1+f2 out. Mixing allows changing a frequency by a non-integer relationship. You have heard this used in the voice distorters used on TV to mask mob informants - they mix the person's voice with a low-frequency signal to change the pitch of the speaker's voice. This is also the basis of any modern superheterodyne receiver - you mix two different (heterogenous) signals together.
The idea is to take the signal from whatever frequency it is on, and move it to the frequency you have designed your circuit to work at - an "intermediate frequency", or IF. You then filter the signal, amplify it to a specified level, and repeat as necessary to get the signal where you want it. For example, a standard FM radio might go from the broadcast frequency to a 10.7 MHz first IF, then to a 455 kHz second IF, then finally to the FM detector circuit.
Eventually, in a design like GnuRadio, you sample the signal. The tricky bit is you have to sample at a frequency not less than twice the highest bandwidth in the signal (Nyquist's criterion). For a 6MHz wide TV signal, that means you need to sample at not less than 12 million samples per second.
Then, for a system like HDTV, you are dealing with a complex signal - and I mean complex as in sqrt(-1), not just as in "not simple" - you need both the real (in-phase, or I signal - the "real" part) and the quadrature (out-of-phase, or Q signal - the imaginary part). The signal is 8VSB - eight level vestigial sideband. So you have to do carrier recovery and tracking (because the carrier itself was removed - that is what makes it a sideband signal), then you have to convert the signals from the analog RF signal into one of 8 levels (slicing is the technical term). However, you have to slice accurately in 2 dimensions - you have to slice at the correct level (is
Finally, once you have a symbol stream, you then have to do all the foward error correction - you have to de-interleave the signal (think of unshuffling a deck of cards) - interleaving is done so that a transient interference (like a lightning strike) doesn't scramble adjacent bits - the errors are spread out.
Then you do your block error correction - this can undo a small number of bit errors per block (again, that's why you interleave the signal: so that block error correction needs to only correct a few bit errors per block).
Then you do some more protocol recovery, and you have an MPEG stream.
Normally, you do this sort of stuff with a big FPGA or an ASIC. The GnuRadio folks are doing it in software. The up side is that you can more easily tweak the code. The downside is that you are not going to be real-time for a few more iterations of Moore's "Law".
What gets to be REALLY fun is when, in addition to all of the above, you have to compute parametrics on the signal - not just recover the bits, but measure how far out of ideal the signal was (that's the sort of stuff I do for a living.) When you do that, you have to do all of the above, THEN once you have an error corrected bit stream you have to regenerate an ideal signal and compare the received signal against it, and measure how far away from the ideal signal the real signal is.
And THAT is when you start using multi-GHz processors, 10 million gate FPGAs, big-ass DSPs, and all sorts of other fun stuff.
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Also, keep in mind that the popular CRT and projection projection TVs will purposily overscan the picture such that some of the lines are pushed outside of the viewing area. So, while 1088 lines are broadcast, a projection TV may only show 1076 of them and clip 6 lines each from top and bottom. If overscanning results in only 4 lines being clipped then you will actually see only 1080 of the 1088 lines of MPEG-2 stream.
The width of 2730 pixels appears to be intended get close to the correct aspect ratio when displayed on a computer monitor. Based on how the people's heads look on my monitor, it seems to be a little over stretched. But when I return the images to 1920x1088, they clearly look squeezed.
Actually, 20MHz isn't so bad - I work with 40 Msample/sec 12-bit flash converters, and there are 100 Msample/sec 12-bit flash converters on the market.
However, you DON'T build things like this with your brother's wood-burning kit and a old nail - These parts come in surface mount packages, and your board has to be carefully designed to maintain proper impedance matching on the RF traces, as well as having excellent grounding (RF and digital grounds meeting at one and only one point, ground planes cut as needed to prevent current loops, etc.).
Lastly, you need a proper dithering circuit to introduce noise equivelent to 1/2 of the least significant bit, in order to shape the quantization noise out of the frequencies of interest. Otherwise, you end up throwing away a couple of bits of resolution.
Those are the sorts of things you have top-notch RF designers laying out, and a top-notch fab build for you - either by having such a fab working for you, or by contracting it out.
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