Thanks Duane.
And just to be clear - I'm talking audio noise here (not birdies).
This noise is NOT present if you bypass the dsp loop (cables 54/56),
meaning if you restrict the audio path to the IF/AF board alone. And the
DSP loop consists entirely of the two cables plus the one CODEC chip U11
(because on the other side of the CODEC chip everything is digital).
If you want to hear this noise in isolation, just turn RF Gain to minimum
and AF Gain to maximum with headphones on. You can also clearly hear the
encoder noise then if you turn the VFO knob.
Barry N1EU
On Sun, Apr 5, 2015 at 6:17 PM, Duane Calvin <ac5aa1@gmail.com> wrote:
> If I recall correctly, the VI+'s and maybe the VI's as well, had these
> residual noises. Individual radios had more or less of this noise. A lot
> of work was done to try to fix it, and the leading answer was to re-orient
> the cables interconnecting boards, etc., in a way that reduced that noise
> pickup. I don't remember what the subject of those threads was, but it was
> covered some time back (resulting in variable results) quite a while ago.
> I'm thinking it was maybe in the late 1990's or so?
>
> 73, Duane
>
> Duane Calvin, AC5AA
> Austin, Texas
> www.ac5aa.com
>
>
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Barry
> N1EU
> Sent: Sunday, April 05, 2015 9:12 AM
> To: Discussion of Ten-Tec Equipment
> Subject: [TenTec] Digital noise in Omni 6+ audio
>
> There's a fair amount of low-level objectionable noises (high-pitched
> tones, tuning encoder noise, etc) in the Omni 6+ receive audio. It
> detracts from what is otherwise a fantastic sounding receiver. Using the
> LP function gives some, but not complete, relief to the high-pitched
> tones.
>
> Has anybody investigated/analyzed this to any degree? I would think that
> the noise must be introduced where the IF/AF board audio loops to the CODEC
> (via cables 54/56) on the logic board for dsp processing. I pulled the
> logic board and was surprised to find that the CODEC chip's "analog" ground
> U11-17/18 is isolated from the rest of the logic board and is only
> connected to the shield of cables 54/56. Yet the shield of cables 54/56 IS
> connected to chassis ground back on the IF/AF board. This just leaves me
> scratching my head - has anybody else looked at this circuit or can
> otherwise comment on this grounding scheme?
>
> I also looked at the +5V supply to the CODEC chip U11 and no glaring issues
> jumped out at me.
>
> 73, Barry N1EU
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