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Old 29th Dec 2009, 8:25 pm   #11
G8HQP Dave
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Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
Default Re: Homodyne/Direct Conversion

Quote:
G8HQP Dave has confused me! Until now, I had considered a homodyne to be a direct conversion receiver, with the locally generated carrier derived from the input itself with suitable limiting and filtering. so the frequency is always right. In other words, it's a special case of a synchrodyne (which does have a local, critically tuned oscillator, with PLL or some other sync system).
When I read this I wondered if I was confused. However, after checking it seems that some people use homodyne in this sense (i.e. LO derived from incoming signal) while others use it as a synonym for synchrodyne. It has also been used for receivers which use the oscillator from an associated transmitter e.g. Doppler radar speed gun.

Whatever you call it, the problem remains of extracting/producing a signal with the right frequency and phase. A PLL can be complicated. A filter requires accurate tuning. You can ease requirements if you can guarantee that AM negative peaks will never completely remove the signal.
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