[time-nuts] Why a 10MHz sinewave output?

Bob Camp lists at rtty.us
Mon Feb 6 17:42:05 UTC 2012


Hi

Differential signaling does indeed take care of a bunch of stuff. The gotcha
is that both sender and receiver need to agree on levels and stuff like
that. Most of these logic families have pretty short life spans if you
include supply voltage dependant stuff. Could you work it out over the
decades - yes. Would it be a pain to do 1960's style stuff today - yes
again. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of paul swed
Sent: Monday, February 06, 2012 9:15 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Why a 10MHz sinewave output?

Indeed the long cable runs are tough. Though today we have differential
cable drivers that do quite well to the Ghz range. But certainly back in
the dark ages the sine wave was a very reasonable way to go.
Regards
Paul

On Mon, Feb 6, 2012 at 3:56 AM, Attila Kinali <attila at kinali.ch> wrote:

> On Sun, 05 Feb 2012 19:50:28 -0800
> bob grant <bobgrant at fastmail.fm> wrote:
>
> > Why is 10MHz output of many sources or distribution amps in the form of
> > a sinewave?
> > Is it something to do with signal reflections or ease of isolation?
> >
> > Since zero crossing detectors are susceptible to noise wouldn't a fast
> > TTL square
> > wave be more appropriate for signal distribution within a equipment
> > rack?
>
> The advantage of a sine wave is that you have a single, bounded frequency.
> A square wave has quite strong components at odd multiples of the base
> frequency, theoretically going up to infinity. To get a "good" shape
> of the signal you need at least the first three of the harmonics,
resulting
> in a seven times increased bandwidth need.
>
> Beside of the more complicated handling of the higher frequency
components,
> you also have to think about dispersion of the signal if you go trough
> filters or use longer cables.
>
>                        Attila Kinali
>
> --
> The trouble with you, Shev, is you don't say anything until you've saved
> up a whole truckload of damned heavy brick arguments and then you dump
> them all out and never look at the bleeding body mangled beneath the heap
>                -- Tirin, The Dispossessed, U. Le Guin
>
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