"David Nebenzahl"

http://en.wikipedia.org/wiki/Direct-conversion_receiver

OK, so this is why I absolutely *hate* Wikipedia. Here's the lead
paragraph in the article:

In telecommunication, a direct-conversion receiver (DCR), also known as
homodyne, synchrodyne, or zero-IF receiver, is a radio receiver design
that demodulates the incoming signal by mixing it with a local
oscillator signal synchronized in frequency to the carrier of the wanted
signal. The wanted modulation signal is obtained immediately by low-pass
filtering the mixer output, without requiring further detection. Thus a
direct-conversion receiver requires only a single stage of detection and
filtering, as opposed to the more common superheterodyne receiver
design, which converts the carrier frequency to an intermediate
frequency first before extracting the modulation, and thus requires two
stages of detection and filtering.

Now, class, how many things are wrong here? (And please correct *me* if
I'm incorrect):

** Only one error.

A basic superhet has two stages of filtering ( RF and IF) followed by one
stage of detection.


o Is their explanation of how DCR works even correct? I don't understand
the business of mixing the signal with a LO signal: why would you do that?

** To shift the modulation down to base band - silly.


They're a little vague: does "synchronized in frequency to the carrier"
mean *exactly* the same frequency as the carrier (???),

** Yep - that is exactly how it works.

In the case of an AM receiver, the original carrier can be extracted and
then mixed with the original AM signal to recover the modulation. Some
hi-fi AM tuners worked this way.


If I were in front of a firing squad and had to try to describe DCR
without actually knowing what it is, I'd guess(tm)(R) that it's a bunch of
tuned RF stages followed by a detector.

** The you would be justifiably shot.

Cos that describes a TRF receiver.


Anyhow, I think I've shown that even if I'm way off base, Wikipedia
articles tend to be extremely badly written, if not outright full of
doubtful information.


** Bob Dylan wrote a song about people like you.



...... Phil