Tech Info

Copy'nPaste

Hi, I'm a noob when it comes to DSO type scopes, so,
what is the highest frequency sine/sawtooth/square wave that the PropScope can display ?
Will it for example show a reasonable representation of a PAL video waveform ?

I picked up that Hanno is working on software that can decode the more common types of data strings, now THAT would be a huge selling point !

Regards,
Copy'nPaste

Copy'nPaste

"Bump" ^

Nobody ?

I really need this info, please :smilewinkgrin:

hover1

A search of the PropScope threads, found this thread:

http://forums.parallax.com/showthread.php?t=121211

Jim

Copy'nPaste wrote: »

"Bump" ^

Nobody ?

I really need this info, please :smilewinkgrin:

Copy'nPaste

Thanks Jim,
I did search, honest, but missed that one
12.5 MHz analoque waveform sound ok to me :scool:

The most I require is to look at a baseband video signal, of which the highest frequency component is about 5.5 MHz, so I can safely assume the PropScope is up to the task

Actually, reading the previous link, my understanding is to sample a waveform 10 times/bits, means that at 25 MS/s I can only sample a 2.5MHz waveform ......
Mmm, seem to have confused myself now.

David Carrier

The PropScope will show a PAL signal with reasonable quality. The 12.5 MHz cutoff is for detecting the presence of the signal. If you put in a square wave at under 12.5 MHz, it will show up pretty well, but you won't be able to tell what type of waveform it is. At 5.5 MHz, a sine wave will start looking like a sine wave, but your peak-to-peak measurements may be a little short. A 2.5 MHz sine wave would be very clear.

— David Carrier

Copy'nPaste

Thank you for the reply David, so I am correct that the highest frequency waveform that can be accurately sampled, would be just under 3 MHz

That still beats my old Po Scope, that can only do 20 KHz :smilewinkgrin:

David Carrier

It is still a bit more complicated than that. Most oscilloscopes are limited by their bandwidth more than they are by their sample rate. For example, I have a Tektronix TDS 1012 on my desk that can sample at 1 Gsps with a bandwidth of 100 MHz. The bandwidth doesn't instantly cut off, but it fades away, so the frequency specified is the point where the signal passes through with half of the original voltage peak to peak. The PropScope only samples at 25 Msps, which pales in comparison to the $1,400 Tektronix oscilloscope. The bandwidth, on the other hand, is about the same, near 100 MHz.

Many scopes have a bandwidth of about 1/10th of their sample rate, so measuring a wave at 1/10th the sample rate would still end up with half of the original voltage peak to peak. Since the PropScope bandwidth is well above the sample rate, you can accurately make measurements of any repeating wave at less than 12.5 MHz, but the image displayed will have major aliasing. For a non-repeating waves it depends on the wave form. If you have a square wave at 6.25 MHz, you are guaranteed to catch at least one measurement per period while the signal is high and one while it is low. For a sine wave, you are never guaranteed to make a measurement at the peak voltages, but the more measurements per period, the more accurate the reading.

Like I said earlier, a 2.5 MHz wave would be very clear, but that doesn't preclude higher frequency waves from being clear too, it mostly matters what you are measuring. You can try it out with just the PropScope. Set the DAC to 5.5 MHz, then switch channel 2 to display the output of the DAC. It will look the same as connecting a 5.5 MHz wave into the PropScope.

— David Carrier