[Elecraft] Elecraft Digest, Vol 130, Issue 53

[Alan Ibbetson]

Steve,

So they did something to reduce CODEC artifacts. Not just AGC mods. 
Interesting. And the talk of lower AF cutoff selection is news to me: 
were you aware of it?

Alan

On 24/02/2015 19:05, elecraft-request at mailman.qth.net wrote:
> Date: Tue, 24 Feb 2015 09:27:42 -0800
> From: Wayne Burdick<n6kr at elecraft.com>
> To: jim<jbollit at outlook.com>
> Cc:elecraft at mailman.qth.net, "'Wes \(N7WS\)'"<wes at triconet.org>
> Subject: Re: [Elecraft] Sherwood Engineering Tests
> Message-ID:<966816B7-51DA-4F7E-ACAF-16CBCACB6C7E at elecraft.com>
> Content-Type: text/plain; charset=us-ascii
>
> Jim (et al),
>
> The K3's audio has improved due to three factors in the past couple of years:
>
> - a low-noise, low-pass audio filter stage was added to the DSP board, eliminating high-pitched CODEC artifacts
>
> - DSP firmware changes were made to correct AGC linearity and eliminate a CODEC quantization problem
>
> - main MCU firmware was modified to allow the user to select the lower AF cutoff in CW mode (100/200/300 Hz) by adjusting the lower edge of the crystal filters
>
> With the above changes in place, we carefully measured the K3's audio spectra and compared it to other radios with the same type of class-AB final AF amplifier IC (most transceivers fall into this category). They are all virtually identical.
>
> Rob, too, told us that the audio spectra he measured on a recent K3 (with new synths and the latest DSP and MCU firmware) was significantly improved from the K3 he measured several years ago.
>
> While it is possible to reduce audio IMD products even further, this typically requires a class-A final audio output stage, which would add perhaps 0.5 to 1.0 amps of additional receive-mode current drain (and an associated heatsink). That is inconsistent with the K3's intended usage, which includes excellent power efficiency for portable applications (Field Day/DXpedition/travel). Also, most users would not notice such a subtle change.
>
> 73,
> Wayne
> N6KR

-- 

Alan Ibbetson
alan at g3xaq.net