Re: What's the use of a 192 kHz sample rate?

On May 5, 3:04 am, nos...@[EMAIL PROTECTED]
 (Don Pearce) wrote:
> On Sun, 4 May 2008 19:54:57 -0700 (PDT), rickman <gnu...@[EMAIL PROTECTED]
>
> wrote:
>
> >I am not an RF guy and the figure I actually remember was 150 dB.  I
> >hedged it a bit as 150 sounded rather extreme to me.  I dunno if 150
> >is anything outside of ordinary or not.
>
> OK 150 - different bandwidth, then. The basic thermal noise at the
> front end of a receiver is -174dBm + 10 log(bandwidth) + noise figure.
> A noise or interference level that desensitizes that by 1dB will be
> about 10dB lower than that level. You need to do the know the
> bandwidth and noise figure to know the significance.
>
> What is significant is that this receiver has a desensitization limit
> for interference that it throws at itself. I have never, ever come
> across that before - it is always an external spec; you design the
> internals so it doesn't interfere.

I have *never* seen a commercial receiver that did not generated self
interference.  They normally are much more concerned with cost and are
willing to live with a few spurs of noise in the spectrum.


> >When you say that it costs too much to go around the design cycle many
> >times, you clearly don't know much about the military procurement
> >process.  On the last radio that they built while I was there, they
> >were up to rev 14 of the board that had nothing but the UI controller
> >and external interfaces.  You need to remember that often the
> >development process is cost plus and the customer is *asking* for
> >tough specs.  It is only when they can't be delivered that they back
> >off.
>
> Iteration 14 and the company was still in business? Anyone can afford
> to do it again if they can't do it right. Was this a "cost-plus"
> contract? Three or perhaps four was more the number I had in mind.

You still don't understand the government procurement process.  The
company doesn't pay for this stuff.  The government pays for
development as well as the product.  That is one of the reasons that I
don't work there anymore.  I have a strong drive to get it right the
first time, literally.  But the politics meant that anyone in the
company could raise a stink about any silly imagined potential problem
and I would get pressure to change the design, *after* the board was
built.


> >What is really funny is that you are getting wrapped around the axle
> >about my use of this figure when that was really just an aside to an
> >aside of my original point.  Funny how these discussions get so far
> >off topic.
>
> If you like. It was clearly a number you threw in because it sounded
> impressively big, even though you hadn't a clue what it meant.

You don't have to be insulting.  I may not know RF by chapter and
verse, but I have a feel for the issues.  I remember very clearly the
issue that was being discussed when I was given that number, I just
don't remember the units.  Lets face it, we all talk about dB in
context and know exactly what is meant.  But at some point *which* dB
is being discussed can be forgotten.  I still get mixed up when
figuring dB in phone lines, but when I have to I can go back to
references and figure out exactly what is correct.


> >Did you read my post which used the original 140 dB figure?
>
> Yes. It was nonsense.

Then why are you bothering to discuss this with someone who posts
nonsense?  Are you compulsive-obsessive?  You are still discussing an
issue that has nothing to do with the original point.  Do you want to
discuss the original point or are you just going to harp on this one
tiny detail?