[LAD] Smallest, simplest, silliest SDR?

Gene Heskett gene.heskett at verizon.net
Sun Feb 28 04:06:02 UTC 2010

On Saturday 27 February 2010, Tim E. Real wrote:
>On February 27, 2010 07:50:07 pm Gordon JC Pearce wrote:
>> On Sun, 2010-02-28 at 01:41 +0100, fons at kokkinizita.net wrote:
>> > On Sun, Feb 28, 2010 at 12:40:00AM +0000, Gordon JC Pearce wrote:
>> > > I wanted a very simple SDR with jack inputs and outputs for a
>> > > demonstration I was doing.  I had a look at the DSP guts of dttsp and
>> > > quisk, and sat down to code.
>> >
>> > Forgive my ignorance, but what is an SDR ?
>> Software-Defined Radio.  Basically you downmix incoming RF to the audio
>> range with two mixers fed 90 degrees out of phase.  You can then munge
>> this in various different ways to tune and demodulate various different
>> radio signals.
>> Gordon MM0YEQ
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>I read about this in Nuts And Volts magazine.
>They describe in some detail how SDR works and neat DSP techniques
> in general.
>I searched the web but could only seem to find Windows related stuff.
>Some more Linux stuff would be cool.
>One still needs to build or buy a front-end first though, right?

Build it.  In 1975, RCA was making an IC for the FM detector that claimed
  <0.1% distortion and at least a 60db SNR for tv and fm radio rx use, the 
type CA3089-E.  They were about $3 the last time I bought a onsie.  14 pin 
dip package.  I would imagine that even better integrated circuits are 
available today for that.  That one needed a superhet front end that could 
give it 400 microvolts to achieve that <0.1% THD, and delivered about 400 
millivolts of audio.

Cheers, Gene
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