Re: KX2/3 DSP AM Demodulation

Posted by Alan Bloom on Sep 10, 2017; 3:38am
URL: http://elecraft.85.s1.nabble.com/KX2-3-DSP-AM-Demodulation-tp7634311p7634318.html

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
>>
>

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