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, [email protected] wrote:
Date: Tue, 24 Feb 2015 09:27:42 -0800
From: Wayne Burdick<[email protected]>
To: jim<[email protected]>
Cc:[email protected], "'Wes \(N7WS\)'"<[email protected]>
Subject: Re: [Elecraft] Sherwood Engineering Tests
Message-ID:<[email protected]>
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
[email protected]
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