Wednesday, April 24, 2013

A nice discussion on ADC !

Is it possible to record or capture a broad range of frequencies for example from 55MHz to 550MHz all into on file? 

I'm assuming that you mean that you want to capture *everything* between 55MHz and 550MHz at the same time, with nothing left out.

The Nyquist criterion says that you need to sample at at least twice the the bandwidth of interest.  Reality says it's more like 2.2 times.

In the example above, the bandwidth of interest is 550M - 55M = 495M. Thus you'd need to sample at a minimum of 990M samples/sec.  Call it 1GS/s.

1GS/second A/D's are available, typically with on the order of 8-bits.

The other downside is that if you're covering 55M - 550M, you're going to have lots of very weak signals and lot of very strong signals in that range.  Thus you're going to need *lots* of dynamic range if you want to see them.  Way more than 8-bits.

Of course you'd also need a raid array that was capable of sustaining writes at 1GB/sec.  A good SATA drive will do about 50MB/s, so if you striped 20 of then together, and had a system that could sustain 1GB/sec of i/o, you'd have that requirement covered ;)

In theory it's possible.  In practice very hard.

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