[Elecraft] K3 DSP LPF daughterboard - What is an artifact and where can you find them?

[Don Rasmussen]

Thanks to Doug for the clarification of the hardware aspect of the DSP board upgrade. This has allowed me to do some research with my own K3's. 

First of all, the term "artifact" seems to be used these days as a catch all. I have heard "rumbles", funny pops and ticks that were seemingly in the foreground of my IC756 and have taken a very negative view of this - DSP artifact generally means to me, odd beyond the point of accepting under normal conditions. I have analog ears, guys who got their first HF with DSP are probably okay with that type of thing.

I went searching for an artifact in the K3 transceiver having not encountered one before. I remembered that I had the upgraded DSP board for low range audio, but unfortunately a very early one that had no lettered marking on it at all, and no daughterboard. So, I was 99% confident that my K3 was ready to exhibit some artifactual behavior, and I would decide if it was objectionable enough to want the $24 upgrade LPF. 

I searched NABBLE and found one of the first reports of this in early Spring to be sounding like "Jingle bells". Hmmm, never heard that. But I knew to look for "jingle bells" at approximately 4 khz and 78db down (weak). I put the K3 on 7 Mhz LSB at night and found a strong SWL signal. I went into the RX Eq and put all sliders at negative 16 EXCEPT number 8 (rightmost) which I put at +16. 

What did I hear? "Sleigh Bells"!. That is quite different from Jingle Bells and although disappointed, it made more sense. ;-) It was plain as day - I am assuming I have found the artifact. 

I pressed the CLR button to set the Rx EQ to FLAT, and I seriously could no longer hear this "artifact". I cant think of any scenario, ever when that rightmost EQ would be above ZERO. But for those that want to hear up there in dog whistle range, or those that can hear it naturally better than I can using a practical EQ setting, Elecraft has gone the extra mile. I hear as well as anyone as a reference, but as Doug suggests, the headphones may be a possible factor. I favor the speaker, 2 of them in fact.  

I applaude Elecraft for going to all the trouble and expense of engineering a daughterboard for this, and maintain once again that to my ears, K3 is the only IF DSP transceiver that sounds analog. The AGC is Q5, no artifacts in the foreground, and minimal DSP filter noise.

Just as a point of reference and no Icom bashing here, but Icom produced a document when the 756Pro was introduced, explained "rumble" and suggested that if you were the type to enjoy record albums, etc. - you may not like the sound of their transceiver. I have no idea what Elecraft did differently.  

I won't be adding the LPF mod - at $24 bucks. It's cost is trivial and I -enjoy- applying mods to my sets, but if there was ever a case of not broke don't fix, this is it for these ears.

73,
Don