[hpsdr] New entry in the (almost) SDR arena

[Philip Covington]

On 1/23/07, Howard Long <hlong at btinternet.com> wrote:
> Folks
>
> > Basically they are paying $159 or $350 for an ADC to use
> > with the SDR-1000 (or even a SoftRock!!!).  If you look at
> > it this way the $95 for a LTC2208 130 MSPS ADC seems pretty
> > cheap.
>
> ...plus a digital down converter, then for TX too digital upconverter and
> DAC.
>
> I went as far as purchasing parts and evaluation boards for a design just
> over two years ago, but after about four months I redesigned using the
> QSD/QSE method for two reasons: (1) the programming of the DDCs and DUCs was
> very complicated, more than my DSP knowledge at the time was comfortable
> with, and perhaps more fundamentally (2) the high power consumption of this
> combination was not compatible with the design criteria.
>
> The DUC/DDC I used had the lowest power consumption for any combination I
> could find at the time, and this was a TI GC5016. It was only available in a
> BGA package, then costing ~$85 per device. For development I purchased a BGA
> socket adapter that broke out the pads for mortals to solder - that cost
> $400!
>
> At that time the state of the art was 14 bits of ADC at 125MSPS (TI/Burr
> Brown ADS5500), so unless you get smart with oversampling, the dynamic range
> is likely to be less that QSD/QSE.
>
> 73, Howard G6LVB

A lot has changed in the last few years.  The DDC/DUC can be done
completely in a Cyclone II FPGA - you don't need a separate DDC/DUC
chip.  I can't speak for the TI/GrayChip parts, but the AD DDC/DUCs
are easy enough to set up - about the same as setting up the AD DDS
chips via SPI.  As far as spending $400 on a BGA socket, hmm - it
would have been cheaper just to have a prototyping PCB made to bring
the BGA pins out to pads.  I've done this for work projects at $51 per
board.

The SDR-1000 is a good example.  At the time it used the best DDS chip
available from Analog and it *is* a power hungry SOB.  The chip was
not cheap either.  The newer 99xx DDS chips are less power hungry but
even more expensive.  The newer 99xx DDS chips need a very low jitter
clock in the 400 - 500 MHz range which is not inexpensive either.  The
SDR-1000 uses an expensive 200 MHz Valpey-Fisher oscillator to get
good phase noise performance.  You could use a PLL/microwave VCO
divided down to give you good phase noise performance but that won't
be cheap either.  There is nothing wrong with the QSD/QSE, but for a
high performance* system the cost is not cheap - nor is the power
consumption low because of the PC needed to complete the DSP
processing.

Phil N8VB

* A SoftRock is cheap and will give fair to OK performance.  If you
use it with your on-board sound card you can get away with a pretty
cheap system.

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