Topband: Analog to Digital converter for 1.8MHz

[Richard (Rick) Karlquist (N6RK)]

You certainly want to bandpass filter the input
to get rid of AM BCB signals.  Assuming a passband
250 kHz wide and a stopband 500 kHz wide, you only
need to sample at 1 MSample/s.  (Of course you still
need an "analog bandwidth" of at least 1.8 MHz.)
However, the dynamic range of 71.5 dB may not do
so well in a contest with lots of strong signals.

Rick N6RK

> -----Original Message-----
> From: topband-bounces at contesting.com
> [mailto:topband-bounces at contesting.com]On Behalf Of Steve Ireland
> Sent: Thursday, July 01, 2004 10:06 PM
> To: topband at contesting.com
> Subject: Topband: Analog to Digital converter for 1.8MHz
>
>
> G'day
>
> It seems that the days of converting 1.8MHz signals from analog to digital
> at our antennas seem just about here.  On October 14 last year Texas
> Instruments released its ADS7881 A to D converter - good to 1.8MHz and
> retailing at about US$7 each.
>
>
> >Analog-to-Digital Converter achieves 4 msps.
>
> >Model ADS7881 combines 12-bit resolution, 1 LSB linearity, -91
> dB harmonic
> distortion, 71.5 dB signal-to-noise, and 95 mW power dissipation. It
> addresses high-speed data acquisition needs by providing
> specification with
> input signal frequency as high as 1.8 MHz. Suited for optical networking,
> imaging, and telecommunications, SAR-based unit integrates internal
> reference and reference buffer, and has pseudo-differential,
> unipolar input
> range of 0–2.5 V.
>
> -----------------------------------------------
>
> I'd be interested to hear from anyone on the reflector who has started to
> think about a topband receiver along these lines - a very sharp front end
> filtering system (the old Cohn filters are pretty good), an A to D
> converter followed by a dsp board to do all the filtering.
>
> Vy 73
>
> Steve, VK6VZ
>
>
>
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