On 4/27/2010 12:50 AM, Daniele Tincani wrote:
Hi Alberto,
thank you very much
for clarification. I was misled by the softrock example :-)
Anyway, a doubt
persists...I read on the frontpanel of the R&S SDR that it is a
"digital wideband receiver"...Well, in my "prejudice", "wideband" does
not match with "high-quality", unless the radio contain several
different "narrow band" receivers. Is this (apparent) conflict solved at the
digital signal processing level?
Regards
D
HI Daniele,
yes, it is a prejudice, as a matter of facts.... why "wideband"
should be not compatible with "high quality" ? This stems probably from
the
old analog world, where you had to face conflicting requirements... in
a SDR, "wideband" can mean e.g. that an ADC does directly sample the
incoming RF spectrum at a rate of 150 MHz (there are ADCs capable of
this), thus providing information up to the Nyquist frequency of 75 MHz.
Then you have just numbers, and with numbers you can perform miracles,
if correctly handled (ask to an accountant, if you don't believe me...
:-)
When you have the digitized stream of numbers that represents the 75
MHz chunk of spectrum, you can, if you need to, analyze those
75 MHz with a resolution of 0.001 Hz, yes, one millihertz... changing
on-the-fly where that millihertz is placed on the spectrum, or even its
bandwidth... try that with an old, analog "high quality" radio.... :-)
Of course, you need both the mathematical background in digital signal
processing and coding ability to do that, and these are skills not very
familiar to analog RF engineers that hence look suspiciously to the new
world of SDRs. But this does not mean that it can't be done....
73 Alberto I2PHD
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