[Elecraft] K4: superhet vs. direct sampling

[Wayne Burdick]

The superhet module buys a lot of BDR improvement. But also -- a subtlety I've failed to mention so far -- the superhet module is intended to somewhat improve 2 kHz IMDDR3 *and* make this figure more repeatable. 

Q: Say what?

A: As Rob Sherwood noted many times before finally immortalizing this point in his must-read footnotes, A-to-D converters sharing the same part number are not all created equal. The long-time previous occupant of his Top Spot benefitted from a never-corroborated monotonicity in its ADC's LSBs. An act of god. The product of a very good day at the silicon foundry when, serendipitously, all the bunny suits were defect-free, and no one was exhaling molecules of grain alcohol or other substances from the night before.

That said, most ops can get by without the extra BDR and IMDDR3, because they're not situated in the RF equivalent of the Gulf Stream. Hence the different K4 models. 

73,
Wayne
N6KR


> On Jun 4, 2019, at 5:10 PM, Lyle Johnson <kk7p4dsp at gmail.com> wrote:
> 
> Mark,
> 
> The "20 dB lower than a K3" figure is an estimate for 100 kHz Blocking Dynamic Range rather than the 2 kHz Narrow Spaced Dynamic Range.
> 
> The K3 is listed at 140 to 150 dB (depending on model, synthesizer, etc) on Sherwood's Receiver Test Data page.  The K4 series without the "HD" option are estimated to be in the 120 to 130 dB range, typical of other direct sampling SDR products (Flex, Apache, Icom, ...).
> 
> 73,
> 
> Lyle KK7P
> 
> On 6/4/19 4:00 PM, mark roz via Elecraft wrote:
>> Before putting my money up front for the first run of K4D I need to know what is the dynamic range
>> of the K4D RX at 2kHz spacing. K3 is 105 dB and K4D? If it is 20dB lower than K3 than it would be 85dB-correct?