[Elecraft] Prospective K4

[Wayne Burdick]

Most “pure” SDRs (using wideband direct sampling and no crystal filters) process all incoming receive samples in large packets.This provides some economies of scale for signal processing algorithms, but it does impact latency. In some cases the impact can be dramatic – like 100 to 200 ms QSK delays.

An alternative is to process only the pan adapter data in large packets. If such data is only being used for a spectral display, the latency is not an issue. 

In CW mode or in other situations where latency must be low, time-domain DSP routines can optionally be used for processing data from the slices (signal channels) used for demodulation. Latency as low as just a few milliseconds is then possible, contingent on the level of filtering required. Filtering trade offs can be automated, e.g. in proportion to the QSK delay setting.

Wayne





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elecraft.com

> On May 5, 2019, at 10:50 AM, Mike Markowski <mike.ab3ap at gmail.com> wrote:
> 
> Hi Wayne,
> 
>> On 5/5/19 1:03 PM, Wayne Burdick wrote:
>> Grant Youngman <ghyoungman at gmail.com> wrote:
>>> Flex has always had issues with CW — QSK with too much latency to work to, now, clunky QSK?
>> That latency is due to processing even the demodulation channels in the frequency domain.
> 
> Can you explain this a little more?  It's probably clear to many, but not me. :-)  I think of 'channel' as the RF channel, but this is used differently. A demod channel as opposed to what other sorts of channels?
> 
> Also, since an fft/ifft change over between frequency and time is the norm in SDRs, why does it matter at what point processing is performed?
> 
> Not doubting, wanting to understand.  Tnx es 73.
> Mike ab3ap
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