Pages: [1]   Go Down

Author Topic: What Is SDR?  (Read 7041 times)

KC9KOW

  • Member
  • Posts: 6
    • homeURL
What Is SDR?
« on: March 28, 2007, 05:32:21 PM »

While browsing around the forums, I came across this section, and because i'm semi-new at this, i'm wondering what SDR is and how it works.
Logged

KG4RUL

  • Posts: 3781
    • HomeURL
What Is SDR?
« Reply #1 on: March 29, 2007, 03:50:26 AM »

Check the second-to-last topic from the bottom.

Dennis KG4RUL
Logged

KG6OMK

  • Member
  • Posts: 107
What Is SDR?
« Reply #2 on: March 30, 2007, 10:24:39 AM »

What is SDR?

In short, it replaces radio electronics with software.  

look at an SDR transmitter first:  In the ideal case you have a computer with a DAC (digital to analog converter) the computer sends a stream of numbers to the DAC, the DAC  converts these to voltages.  the voltage goes to an RF ampliphier and then on to an Antenna.  So rather then using VFO, mixers, modulators and what not you simply compute the RF waveform.

In this ideal system you compute the voltage that you want  to place on the antenna a few million times per second and the DAC directly drives the antenna.  In the real world the computer is not so fast and direct computation would only work down in the low HF bands so you have the DAC drive an up-converter.


In a practical SDR receiver you have a tuned RF front end and a down converter that takes RF to IF.  Then you digitize the IF and feed it to the computer where it get demodulated.  This is only slightly different then hooking a sound card up to the AF output of a receiver.  The difference is really just bandwidth.  Typically when sampling IF you sample a few megahertz where as with AF you sample a few kilohertz.



Why?   because you can do things you can't otherwise do.  For example one SDR demo receives two commercial FM broadcast stations and copies each to a different file.  I've seen the  SAME radio with just a software change receive ATSC (HD television)

SDR is really the only way to do some advanced digital modes.  like QAM-256 or DRM (Digital Radio Mondiale)

But way would hams care?  You can build and experiment with cutting edge radio technology with just a keyboard and a text editor, no need for expensive custom RF hardware.

Read here for more
http://www.gnu.org/software/gnuradio/doc/exploring-gnuradio.html

Logged

WA9UAA

  • Member
  • Posts: 364
What Is SDR?
« Reply #3 on: April 05, 2007, 11:49:13 AM »

Hi All,
Check out the SoftRock group on Yahoo. Two band QRP kits, which need a computer/ sound card of course, are in the low $30.00 range.
73,
Rob WA9UAA
Logged

AF6WC

  • Member
  • Posts: 2
What Is SDR?
« Reply #4 on: April 29, 2007, 04:25:09 AM »

I'm sure I'm going to take some heat for this post, but I feel it needs to be said.

Hams across the board should be embracing this new leap, and it is just that, in radio technology. But from what I'm seeing it's just not happening. I see complaining about the user interface (really missing the point folks), while the majority of folks miss the looming gift that has been given to us, a gift which further allows ham radio to stay at the forefront of tech and fix a few "problems" that some folks like to gripe about but never have a solution to.

As I see it software defined radio is an open door that if promoted properly would bring many, many new folks into out community, and realize that the people coming in through projects like GNU Radio are talented and highly intelligent folks. In fact they are the type of people that 20 years ago would have been the tinkers, the guys building rigs from scratch, developing new operating modes, etc. It's just that the tech world is heavily software-centric now. There is only a small community of hardware hackers nowadays (although it looks like hobbyist electronics and homebrew is making a strong comeback), instead the majority of the sharpest tech-minded folks, the ones developing disruptive technology, are poking around in code.

So from that angle this solves the worry and possibly the real issue of being flooded with, as the tone seems to denote, less than desirable people spoiling the ham community now that the code requirement has been pulled from general and up.

Secondly and most importantly, software defined radio is an extremely powerful tool for advancing radio technology. In every other piece of promo literature the claim that amateur radio had and is ahead of the technology curve is hyped. And this was true for the longest time, but honestly the current state of amateur radio tech isn't much to write home about. Sorry IRLP isn't that revolutionary nor is PSK31. Now being able to go from idea, to prototype, proof of concept and into application for a new protocol/operating mode in a time span as short as a few days (no hardware to build, reduced expenses, etc.) creates an environment that fuels innovation and lowers the barrier or even removes the barrier to breakthroughs and innovation.

What we have here is an awesome opportunity to update the state of amateur radio, bring valuable people assets into the fold, continue the greatest traditions and contributions of amateur radio and just plain have fun with pushing the boundaries of what is possible in communications.
Logged

KG6OMK

  • Member
  • Posts: 107
What Is SDR?
« Reply #5 on: April 29, 2007, 07:25:47 PM »

"I'm sure I'm going to take some heat for this....
Hams across the board should be embracing this new leap, and it is just that, in radio technology. But from what I'm seeing it's just not happening.'

There IS a lot of interest in SDR.  You would not think so by watching this forum but my in-box gets maybe 50 messages a day from other lists.  More than I can read or follow. Maybe more SDR related messages than all of all of eham.net forums combined


If you read the lists you see that not every in a ham.  People are using SDR for other things too.  Some examples are GPS receiver, a mode S radar transponder, HDTV Receiver,.... not just ham bands and not everyone working in SDR is a ham.

Very few hams are into building stuff.  Not with solder and not with software.  What?  Maybe 2% would ever build any piece of gear with solder and wire.  Even fewer have the skills to build with software.  But even so that fractional percent is a big number and there is lots of activity. It's just not here.
Logged
Pages: [1]   Go Up