[Elecraft] KX2/3 DSP AM Demodulation

[Alan]

Right, the amplitude of the signal is just the length of the I/Q vector, 
which is sqrt(I^2 + Q^2).  If the receiver is a little off-frequency, 
the I/Q vector rotates (because the phase is constantly changing) but 
the amplitude is still just the length of the vector.

Alan N1AL


On 09/09/2017 08:19 PM, K9MA wrote:
> Never mind:  I think I found the answer:
> 
> https://www.tjhsst.edu/~rlatimer/techlab/Gelbpaper04.pdf
> 
> (The explanation isn't that clear, but I worked through the trig a bit 
> more rigorously, and got the same answer.)
> 
> Basically, the modulating signal, m, is the square root of the sum of 
> the squares of I and Q.
> 
> So really, all the DSP has to do is a little simple arithmetic.
> 
> I should have been able to figure that out.
> 
> 73,
> 
> Scott K9MA
> 
> 
> On 9/9/2017 21:19, 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?
>>
>>
>> 73,
>>
>> Scott K9MA
>>
>