> But modern techniques now provide the selectivity needed without the
> superheterodyne format with all of its issues. The quadrature sampling
> detector is one of those.
The quadrature sampling detector is a large step backward from the
current IF sampling in the K3. I have always felt QSD as exemplified
by Flex radio is a toy compared to a serious radio much like simple
direct conversion transceiver is a toy compared to the K3 or other
modern superhetrodyne transceiver.
If one wants to use modern techniques direct sampling/direct synthesis
should be the approach of the future. While I am sure that Wayne has
a few tricks to make QSD work better than the toys produced to date in
that genre QSD still suffers from significant gain distribution and
spurious response issues. In addition QSD adds issues with gain/phase
balance, and has blocking/overload and dynamic range problems that are
more severe than those in the narrow band (superhet) approach.
73,
... Joe, W4TV
On 12/6/2011 10:12 PM, Ron D'Eau Claire wrote:
> I agree, Joe. The direct conversion (RF to baseband) architecture has been
> around since the earliest days of radio for a reason. The superheterodyne
> format using "intermediate" frequencies offered selectivity that wasn't
> available in the past but at a cost: spurious responses and very sensitive
> gain distribution are just two of the most severe. But 'superhets' were
> better and so became the format of choice.
>
> But modern techniques now provide the selectivity needed without the
> superheterodyne format with all of its issues. The quadrature sampling
> detector is one of those.
>
> We've seen a lot of work in the direct conversion format since the 1950's,
> but development has accelerated rapidly in recent years as any casual review
> of the literature will show. It's exciting that Wayne chose this approach
> for the KX3, given the high-performance engineering skills he has
> demonstrated with the other Elecraft rigs.
>
> 73, Ron AC7AC
>
> -----Original Message-----
> Howdy Gang:
>
> Perhaps I should have made my previous comment regarding the KX3 and my
> "daydream" K4 a bit clearer.
>
> I should have been more specific in terms of the QSD (quadrature sampling
> detector) architecture of the KX3 as related to my "day dream" K4.
>
> While the K3 is controlled via firmware (SDR) it has a conventional superhet
> architecture as opposed to a QSD scheme.
>
> 73, Joe W2KJ
> 7
>
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