Re: KX2/3 DSP AM Demodulation

Posted by k6dgw on Sep 10, 2017; 6:12pm
URL: http://elecraft.85.s1.nabble.com/KX2-3-DSP-AM-Demodulation-tp7634311p7634329.html

Your KX2 isn't really a DC receiver, it has an 8KHz IF which is then
digitized and demodulated in a digital computer executing the demod
algorithms to produce baseband output.

But the original question was simply "what is direct conversion?" and
the answer is, you convert the incoming signal to baseband ... directly
... one time.  What you do with the baseband after that is a separate
matter.  And, you can hear SSB, CW, and AM just fine with a
free-running, reasonably stable LO.

My experience listening to an analog direct-conversion receiver in a low
ambient noise environment is that the RX noise is uncharacteristically
low, almost to the point that I thought something was wrong, like no
antenna.  Then, tuning across a signal, it just sort of pops up at the
expected volume.  Since I've only done this with one receiver, it's hard
to draw meaningful conclusions however. [:-)

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County


On 9/9/2017 7:46 PM, K9MA wrote:

> On 9/9/2017 21:35, Fred Jensen wrote:
>>  A DC receiver converts the signal once to audio.  Regardless of the
>> mechanics [which these days can get very complex], that's really all
>> there is.
>
> Ah, but the only way direct conversion can convert AM to audio,
> without some kind of fancy DSP stuff, is to phase lock the conversion
> oscillator to the carrier.  My KX2 doesn't sound like it's doing that
> when I tune across a signal; it sounds more like a conventional
> superhet AM receiver.  I'm trying to figure out how you take the I and
> Q mixer baseband ("audio") outputs of an AM signal and convert them to
> audio, and in a way that works when the carrier is not exactly zero beat.
>
> 73,
>
> Scott K9MA
>

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