[Elecraft] KX2/3 DSP AM Demodulation

[Don Wilhelm]

Scott,

The KX2/3 is not a direct conversion receiver/transmitter.
Instead, it has a quadrature mixer which converts the incoming RF into 
baseband (or 8kHz IF) I/Q streams which is then sent to analog to 
digital converter.  The output of the A to D converter is a 'bunch of 
bits', which can be manipulated by mathematical processes (DSP) to 
poduce most anything you wish.

So the KX2/3 receiver is similar to a SoftRock receiver which feeds its 
output I/Q streams to a computer soundcard for DSP processing.  With the 
KX2/3, the soundcard and computer are contained inside the box (no 
computer needed).

That is the best I can explain "how it works".
If your study of signal theory also included Digital Signal Processing, 
then look to the DSP algorithms for modulation/demodulation of all forms 
of RF signals.  AM, CW, SSB, FM are all just mathematical formulas by 
which to manipulate data.

The DSP process is more akin to the phasing method of detection.  If you 
want an all analog comparison, look at the phasing receivers that Rick 
Campbell KK7B has designed.  His receivers did "DSP" with analog 
circuits, and the weakness of that approach is only that analog devices 
have component tolerances, while mathematical formulas can produce exact 
results without those tolerances.

73,
Don W3FPR

On 9/9/2017 10:19 PM, K9MA wrote:
> It's been a long time since I studied signal theory in college, but I'm 
> curious as to how AM is demodulated in a direct conversion radio like 
> the KX2/3.  (SSB and CW demodulation I understand.) Does anyone know, or 
> have a reference?