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

On Sun, 4 May 2008 12:28:34 -0700 (PDT), rickman <gnuarm@[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.

d
-- 
Pearce Consulting
http://www.pearce.uk.com