On 10/05/2011 07:11 PM, Nick Foster wrote:
By "no IF frequency" he meant the LO frequency is the same as the RF
frequency. This is called a zero-IF receiver, or direct conversion.
http://en.wikipedia.org/wiki/Direct-conversion_receiver
--n
More precisely, and completely, they use a direct-conversion, quadrature
(I + Q) signal format.
Without the I+Q bits, then the the two side-bands created from mixing
the RF with LO==RF would cause
them to "fold about each other". In the very, very, early days of
direct-conversion designs (way back near
the start of the 20th century), the fact that the two side-bands
overlapped wasn't an issue, because the modulation
mode was typically AM, which "doesn't care" about such things. But
for anything else, you need to use
a complex representation, in order to distinguish (-bandwidth/2-DC)
from (DC-bandwidth/2).
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org
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