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

On May 4, 3:40 pm, nos...@[EMAIL PROTECTED]
 (Don Pearce) wrote:
> On Sun, 4 May 2008 12:28:34 -0700 (PDT), rickman <gnu...@[EMAIL PROTECTED]
>
> wrote:
>
>
>
> >On May 4, 12:18 pm, DigitalSignal <digitalsignal...@[EMAIL PROTECTED]
> wrote:
> >> Hi rickman, can you refer the company who can produce or analyze the
> >> signals with 140 dB SNR? I have never seen one. I guess they are not
> >> using any digital technology, or they are look at very low frequency
> >> signals. Right?
>
> >> Jameswww.go-ci.com
>
> >Thales Communications, makers of military radios.  This figure came up
> >in the context of digital interference with the RF sections.  I was
> >told that the digital noise had to be below -140 dB to prevent
> >desensitization of the receiver.  These units are *very* overbuilt and
> >far surpass anything commercial I have seen.  One spur anywhere in a
> >huge range, 30 MHz to 500 MHz, IIRC and they are back to the testing
> >room to add more copper tape or to put more resistors in clock lines,
> >etc.
>
> A desensitization level is going to be measured in dBm, and -140 is a
> very ordinary figure. If external noise interference is present at the
> input of a receiver, it will add to the inherent noise already there,
> raising it. This is called desensitization. A common interference
> requirement is that a desensitization of no more than 1dB is
> permitted.
>
> The -140 in this instance is just a receiver input level, and nothing
> to do with S/N ratios, dynamic ranges or anything like that.
>
> I would be very surprised if anything military surpassed the spec of a
> commercial design. Far too few units are built to justify the number
> of trips round the design cycle that are needed to remove every spur
> from and maximise performance. That fact that they have to bodge units
> with copper tape to make them work rather bears this out.
>
> Certainly when I was designing low noise converters for domestic
> satellite systems I achieved a guaranteed total noise figure 0f 0.25dB
> at 12GHz, and the entire unit had a works cost price of 11 dollars.
> Nothing military has ever come close to that kind of performance or
> price.

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.

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.

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.

Did you read my post which used the original 140 dB figure?