On 4/17/12 7:15 AM, Robert Darlington wrote:
I need lots of memory on scopes. A buddy of mine I worked with in the
ultrasound world actually yelled at the Tek product management and
asked if they actually *use* oscilloscopes. The answer was a sheepish
no, and yet they felt qualified to develop the products for the
company.
The cheap Aktakom scope I have has plenty. 10 million samples (you
can select less if you want) and will write out to usb thumb drives.
It's definitely a toy scope with lots of noise, but it's useful for
some things.
What we do is send out pulses or chirps and look at what returns.
There are tens of millisecond delays between what we send out and what
we receive and the echos. With traditional low memory scopes we
simply can't get by. Thankfully Tek is learning that memory is cheap
and 2500 samples was hardly sufficient in the 70s, let alone now!
Yes, just like in the radar world (really, ultrasound and radar are
really similar.. same kinds of pulse compression and signal processing)
Back in 1998-1999, I was buying digitizer cards from Gage Applied
Sciences (since acquired by Tek, as it happens), and one of their big
markets was for ultrasound. Same for Signatec (another mfr of fast
digitizer cards for PCs)
Another case where deep memory is nice is when you don't know exactly
when the signal is going to arrive, it's very low SNR, so you want to
record a long time, and then go look for the signal later. But that's
more a data capture problem than a bench oscilloscope problem.
say you were recording off-the-air GPS signals. You want to record a
couple milliseconds, at least (so you get at least 1 code epoch), and
you need to record at least 10 MHz bandwidth. That's only, say, 64,000
samples, but you might want to record a whole 50 bps nav message bit, so
then you need ot record 40-50 milliseconds, and the record length starts
to grow.
Again, that's more of a data recording problem than an oscilloscope problem.
It's the wideband pulsed waveforms where you want to compare pulse to
pulse is where deep memory in an oscilloscope is nice. The digitizer
cards are ok, but "real oscilloscopes" tend to have better input
amplifiers and such.
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