Xref: utzoo rec.ham-radio:13441 sci.electronics:7897 Path: utzoo!attcan!uunet!ginosko!brutus.cs.uiuc.edu!lll-winken!tekbspa!optilink!elliott From: elliott@optilink.UUCP (Paul Elliott x225) Newsgroups: rec.ham-radio,sci.electronics Subject: Re: New cheap 200 kHz ADC: good for digital receiver? Summary: Digital Radio / DSP commnt Message-ID: <2378@optilink.UUCP> Date: 22 Sep 89 17:38:10 GMT References: <1989Sep19.171259.1670@mentor.com> <17673@bellcore.bellcore.com> Organization: Optilink Corporation, Petaluma, CA Lines: 32 In article <17673@bellcore.bellcore.com>, karn@jupiter (Phil R. Karn) writes: > > Antenna ---> Mixer ---> LPF/gain --> ADC -----> DSP -----> DAC -----> audio > > ^ | > > | | > > DDSynth \------> data > > > >A few real RF stages + cheap digital VLSI = high-performance receiver? > > Actually, you'll want two mixers, low pass filters and A/D converters. > The mixers should operate in quadrature so you can do things like SSB > filtering in DSP software. > > Phil Correct me if I'm mistaken, but we can still do the SSB phasing demodulation in software with the receiver as shown in the diagram (assuming blazingly fast processing hardware). The only function of the mixer is to shift the input signal frequency down to a more comfortable range for the A-D and DSP. Of course, if you had REALLY fast hardware and software, you could dispense with the mixer and local oscillator altogether... I vaguely remember a conversation I had with the designer of some sort of (fairly low frequency?) (aeronautical navigation?) receiver, where they did essentially this in an ASIC. It doesn't seem entirely practical to me now, so I'm probably forgetting something critical. I'll post again if I can come up with the details. -- Paul M. Elliott Optilink Corporation (707) 795-9444 {pyramid,pixar,tekbspa}!optilink!elliott "I used to think I was indecisive, but now I'm not so sure."