http://elecraft.85.s1.nabble.com/Comparison-K3-and-SDR-5000A-tp454268p454281.html
I don't believe you can get something for nothing. The sample-in/sample-out
number of samples and time to fill the filter pipeline, as well as empty it.
delayed in time at the output. What is it about the K3 architecture that
>> As I understand it, latency is no longer an issue. Latency issues with
>> the early versions of PowerSDR and the SDR-1000 have been resolved. That
>> being said, signal processing latency is a fact of life for all digital
>> radios. We are talking microseconds,
>
> I beg to differ.
>
> Latency (delay) in a DSP-based radio (or SDR, if you prefer) is caused by
> several things.
>
> The one we can't get rid of is the filter delay. By making "shorter"
> filters (fewer taps), we can reduce the delay through the filter, but at
> the expense of filter performance. We get wider skirts, less ultimate
> rejection, more passband ripple, or some combination of these three
> factors.
>
> However, DSP can be applied in many ways. One sure way to increase
> latency is by processing the incoming signal in blocks. This means you
> collect a certain number of samples, then process them all at once while
> collecting the next block, etc. PC implementations of DSP typically use
> this method.
>
> Another method is to process the signal after each sample. This
> eliminates the block delay. This is how the K3 processes signals.
>
> As an example, let's consider an SDR using 2048-sample blocks (common in
> the SDR world) and 96 kHz sampling. It will take (2048/96,000 =) 22
> milliseconds to acquire this block. This is 22 ms more delay, or latency,
> than a K3 will have, assuming similar delays in each radio for the
> filter(s).
>
> For a real world example, I connected an SDR-14 receiver (with associated
> dual core 3 GHz PC) to the IF output of my K3. I then tuned in an SSB
> signal and listened to it through the K3's speaker as well as demodulating
> it and listening through the PC's audio system.
>
> The audio coming from the PC was very noticeably delayed versus the audio
> from the K3.
>
> This delay or latency may not be an issue in all cases. But in come
> common operational scenarios, like QSK CW or SSB using "syllabic" VOX, it
> can be critical. By paying close attention to such latency issues in the
> architecture of the K3, we are able to provide QSK CW operation at speeds
> well over 30 WPM without "reducing the taps" in the filters or otherwise
> compromising the performance of the radio. The 22 ms additional delay
> cited in the example above would kill QSK performance.
>
> Latency is just one of many considerations that arise when comparing
> radios, architectures, and one's own needs and preferences.
>
> 73,
>
> Lyle KK7P
>
>
>
>
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