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Message started by Rudy on Apr 8th, 2011 at 12:02pm

Title: What is mhz??
Post by Rudy on Apr 8th, 2011 at 12:02pm
I see that Picos new scope(updated?) is rated at 80 mhz. What exactly is this for? A technician I know said that anything over 50mhz is overkill for a car. He said nothing communicates this fast on a car. Is this true? If not can you give examples as to what would communicate this fast? thanks for the help...

Title: Re: What is mhz??
Post by Tom Roberts on Apr 8th, 2011 at 3:00pm

Rudy,

You have to sample at least twice the frequency of a signal just to avoid aliasing.  For best digital reconstruction you need to sample 5 to 10 times signal frequency.

The 4000 series scopes were made to tackle Flex Ray communication, which can be 10MHz.  So, now the dual 80MHz ADCs in the 4000 series scopes can sample that at 8x.

Of course, real time sample rate is a function of ADC speed, record length, and capture time.  So, a large memory depth is needed to be able to maintain robust sample rates at long enough time bases to capture enough signal to analyze.

The 4000 scopes have you covered there also with the internal 32 million point sample memory.

Title: Re: What is mhz??
Post by Dr. Jake on Apr 19th, 2011 at 9:27am
Hertz means laps tah me. Whatever ever it is, it does a so many laps ina second.

80 MHZ is 80,000,000 laps per second. They must some really fast switches to do that...............amazing,aye--mate.?

Must have some really good hinges on tha gates..........

I wonder how many electrons that is between on and off.?

Title: Re: What is mhz??
Post by Tom Roberts on Apr 19th, 2011 at 10:45am

I also assumed the question related to sample rate, although it was not clear.  Maximum samples per second = 80,000,000.

I later saw this was a question that was also asked on the iATN Technical Theory Forum.  A lot of misinformation was provided there including much confusion between sample rate and bandwidth.  They are two completely different things.

The 4423 has a 20MHz bandwidth.  This means that it will not begin attenuating (distorting) the signal until you approach 20MHz.  In other words, the maximum frequency of signal that can pass through the front-end amplifiers.

This all takes place before the signal is even sampled.

As mentioned earlier, you must sample at least 2x signal frequency to avoid aliasing.  So, you would need a minimum sample rate of 40MHz to even come close to making use of the 20MHz bandwidth before the signal became useless.  The Pico 4423 has enough sample rate power to sample at up to 4x the bandwidth.

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