[time-nuts] Programmable clock for BFO use....noise

ewkehren ewkehren at AOL.com
Mon Sep 17 06:25:48 EDT 2018


Good choice                    Bert Kehren


Sent from my Galaxy Tab® A
-------- Original message --------From: Gerhard Hoffmann <dk4xp at arcor.de> Date: 9/16/18  6:30 PM  (GMT-05:00) To: time-nuts at lists.febo.com Subject: Re: [time-nuts] Programmable clock for BFO use....noise 


Am 16.09.2018 um 23:11 schrieb Attila Kinali:
> On Sun, 16 Sep 2018 22:08:19 +0200
> Gerhard Hoffmann <dk4xp at arcor.de> wrote:
>
>> I'm also not a fan of using slowish, slew-rate challenged  logic as a
>> replacement
>> for a low pass. When I want a low pass, I make it from nice,
>> time-invariant RLC.
> Unfortunately, using a low pass after the divider will not
> prevent the down-mixing. The down-mixing happens as an inherent
> property of digital circuits. Any filtering you do afterwards
> will be too late. If you want to have low noise, then the only
> way is to produce a non-square wave signal. Or in other words:
> use a divider built from harmonic mixers*.
Why do you assume that slew-rate limited mixers are any
better than mixers with an ultra-short analog time window
for doing mess?

We should sort that out offline, we are just 20 miles apart?
I propose the Zwickel pub in Dudweiler; I'm there with the
mostly emerited Fraunhofer people on Friday evenings
now & then.        :-)  :-)  :-)
> * That is, if you don't like Λ-dividers or DDS
I do like DDS, and I don't see  a reason for the D/A converters
in front of the mixers. D/A converters remove the fun when you
can just instantiate a multiplier.

Cheers,

Gerhard



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