[Elecraft] K4 DSP bit width

[Bill Frantz]

A friend and I were discussing the K4HD and he said that it 
sounds a lot like the K3S. Well, we both agreed that since the 
K3S has world class receiver specs, that would not be a bad thing.

I started comparing the information about the K4HD with the K3S 
manual and found:

K3S       K4HD   Feature
8.215MHz  ~8MHz  First IF
15KHz      ?     Second IF (if used in the K4)
24         16    ADC width
~30KHz?   122MHz ADC sample rate (WAG for the K3S)
5         2+1    Crystal filters (one empty slot is from a post 
on this list.)


Note: In the K4 FAQ there are forward references to a K4HD 
section, but I couldn't find it on the web site.


Analysis and wild speculation

Both DSPs and ADC technology have had at least 10 years to 
improve between the K3S and the K4. WHile I don't track ADC 
tech, DSPs are computers and we all know what has happened in 
computers. The basic processors are somewhat faster, and there 
are many more cores on a chip. The K4 certain to have taken 
advantage of these improvements.

The K3S uses a 32 bit floating point DSP, and I don't see any 
reason to change that specification for any of the K4 models. 
Not changing means that much of the K3 DSP code should easily 
port to the new DSP.

I don't understand how the basic K4 can get good dynamic range 
with a 16 bit DAC. The K3's 24 bit DAC seems a better choice, 
although getting high speed and wide bit width at the same time 
is hard and expensive.

In the wild speculation department, there seem to be several 
approaches for the K4HD. (1) Run a K3 like superhet with an 
~8MHz IF and digitize that into the DSP. (2) Duplicate the K3's 
2nd IF and use the 16 bit ADC at 15Khz. (3) Use a wider ADC at 
either 8MHz or at 15KHz. Note that one of the features of the K4 
is ease of upgrade to new ADCs.

73 Bill AE6JV

---------------------------------------------------------------------------
Bill Frantz        |"Web security is like medicine - trying to 
do good for
408-356-8506       |an evolved body of kludges" - Mark Miller
www.pwpconsult.com |