[Elecraft] kx3 vs k3

[Don Wilhelm]

You may have to do some study on both analog receivers and SDR receivers 
to understand and appreciate the differences, but let me try to give an 
answer in the way I understand it (others can correct me if I am wrong 
in any area).

The K3 down-converts first to an 8 MHz IF, then converts to a 15 kHz IF 
signal that is passed to an ADC and the digital output is processed by 
the DSP before being converted back to analog audio signals which are 
amplified and sent to the headphones or speaker.

OTOH, the KX3 down-converts direct to baseband (audio range) as I/Q 
signals (each with its ADC) and the DSP processes those quadrature 
signals and then sends the output to a DAC to obtain audio which is then 
amplified.

That means that the KX3 will be more like other SDR receiver designs 
than the K3 (which is also technically an SDR).

Which is better?  That is a difficult question to answer.  The 8 MHz IF 
of the K3 allows crystal roofing filters to be inserted in the path to 
keep strong signals which are out of the filter passband from 
overloading the ADC (which would result in garbage data out).
The KX3 can have roofing filters, but they will be active filters in the 
audio range - they will do the same thing, but I expect the dynamic 
range of the KX3 will not be as great as that if the K3.
There are advantages for both approaches.  The K3 design is more 
complex, but allows more controls in the analog IF system (note both 
analog and DSP Noise Blankers for one example).

I do not expect the KX3 to have performance characteristics that are 
equal to the K3, but it may be close.
You might want to think of the KX3 as a "full SDR" as opposed to the K3 
which is a combination of analog and SDR - both of which are complete 
receivers without the addition of a computer, and that is different than 
most other SDRs on the market.

73,
Don W3FPR

On 9/4/2011 5:24 PM, KC6CNN wrote:
> The KX3 and K3 have different engineering for the receive.
> Can someone explain the difference and which one would be better?
>
> Thanks.
>