[Elecraft] KX2/3 DSP AM Demodulation

[K9MA]

On 9/9/2017 22:13, Don Wilhelm wrote:
> The KX2/3 does not convert directly to audio.
> It converts the RF to "baseband" which is a zero frequency IF (in the 
> KX3).  The KX2 has the "8kHz shift" built in at all times, so the IF 
> is 8kHz rather than baseband.
> The KX3 can shift to the 8kHz IF if there is breakthrough of AM 
> broadcast stations.
>
> Again, these are not Direct Conversion receivers.

I didn't realize the KX2 used an 8 kHz IF, though I see it is mentioned 
in the manual.  I guess that means the image is 16 kHz away from the 
desired signal, and is suppressed by the I/Q demodulation, as in a 
phasing transmitter.  It does explain why the post mixer amplifier 
cutoff frequencies are so high.

However, is not the KX3, when it's using the zero frequency IF really a 
direct conversion receiver, just with quadrature mixers so one side of 
zero beat can be suppressed?  Perhaps the term "Direct Conversion" is 
avoided because of the lack of opposite sideband rejection in 
conventional DC receivers.

Just out of curiosity, why does the KX3 not use the 8 kHz IF all the 
time, as does the KX2?

73,

Scott K9MA

-- 
Scott  K9MA

k9ma at sdellington.us