New cheap 200 kHz 14-bit dual ADC chip = digital HF receiver?

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3 total messages Started by Mike Butts Thu, 21 Sep 1989 16:23

#247

Author: Mike Butts
Date: Thu, 21 Sep 1989 16:23

30 lines
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Here's something I recently posted to rec.ham-radio:

The current Electronic Design (9/14/89) has a piece on the new Burr-Brown
PCM1705P, a monolithic dual analog-to-digital converter.  It runs at 200 kHz,
gives 14-bit accuracy and 18-bit resolution, and costs $27 in 1K quantity (I'd
guess <$50 in onesies).  It's designed for high-end home audio, DAT and effects
and such, but the article is mostly about how you can hook it to a DSP & use
it for medical, telecommunications, spectrum analysis, imaging, etc.

I wonder if any DSP radio experts out there can comment on whether this chip,
with an 80 kHz or so IF front end on the input and a DSP on the output might
make a practical HF receiver, using the DSP for most of the selectivity, gain
control, and demodulation?  Is it reasonable to use that low an IF?  Could you
use both ADCs on the chip to alternatively sample a higher IF, like 160 kHz?

Imagine how fast, cheap ADCs and DSPs could cause a revolution in receiver
design (especially when we get cheap ADCs and DSPs that can handle several
MHz IFs, and direct digital synth chips to match):

  Antenna ---> Mixer ---> LPF/gain --> ADC -----> DSP -----> DAC -----> audio
                 ^                                |
                 |                                |
              DDSynth                             \------> data

A few real RF stages + cheap digital VLSI = high-performance receiver?
-- 
Michael Butts, Research Engineer       KC7IT           503-626-1302
Mentor Graphics Corp., 8500 SW Creekside Place, Beaverton, OR 97005
!{sequent,tessi,apollo}!mntgfx!mbutts         mbutts@pdx.MENTOR.COM
Opinions are my own, not necessarily those of Mentor Graphics Corp.

Re: New cheap 200 kHz 14-bit dual ADC chip = digital HF receiver?

#257

Author: Ted Dunning
Date: Fri, 22 Sep 1989 17:01

27 lines
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In article <1989Sep21.162329.2416@mentor.com> mbutts@mentor.com (Mike Butts) writes:

   Here's something I recently posted to rec.ham-radio:

	...

   I wonder if any DSP radio experts out there can comment on whether
   this chip, with an 80 kHz or so IF front end on the input and a DSP
   on the output might make a practical HF receiver, using the DSP for
   most of the selectivity, gain control, and demodulation?  Is it
   reasonable to use that low an IF?  Could you use both ADCs on the
   chip to alternatively sample a higher IF, like 160 kHz?

if you are already down to an if < 200 KHz, then you have either done
most of the work of getting the selectivity you want, or you haven't.
similarly, gain control must be done earlier.  demodulation can be
done digitally (certainly for fm), but there may well be better
digital demodulation methods than just digitizing and then (ds)
processing

--
ted@nmsu.edu
			Most of all, he loved the fall
			when the cottonwoods leaves turned gold
			and floated down the trout streams
			under the clear blue windswept skies.

Re: New cheap 200 kHz 14-bit dual ADC chip = digital HF receiver?

#402

Author: Tom Anderson
Date: Mon, 25 Sep 1989 23:20

28 lines
1864 bytes

>I wonder if any DSP radio experts out there can comment on whether this
>chip, with an 80 kHz or so IF front end on the input and a DSP on the
>output might make a practical HF receiver, using the DSP for most of the
>selectivity, gain control, and demodulation?  Is it reasonable to use
>that low an IF?  Could you use both ADCs on the chip to alternatively
>sample a higher IF, like 160 kHz?

Yes, you can make an IF with digital parts.  The HP8560A Spectrum
Analyzer has a digital IF in it.  I can't comment specifically on the
Burr-Brown part.  But if I had two channels, I would sample the IF
signal in quadrature instead of alternately.  This way you get the full
benefit of twice the sample rate of a single converter, and you get to
do some DSP tricks with the quadrature inputs.

Notice that any gain or offset mismatch between the two A/Ds (when
sampling alternately) would look like a signal at half the sample rate.

Don't forget to put a good S/H amp in the system.  Parts designed for the
audio market might have some nasty distortion characteristics when the
input signal is at a high frequency.

A book with some ideas on this subject is "Communication Receivers" by
Ulrich L. Rohde and T. T. N. Bucher.

Tom Anderson           Hewlett-Packard   Signal Analysis Division
toma@hpsad.hp.com      "It's only hardware"

Views expressed are my own and not Hewlett-Packard's

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