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AnaLog Services, Inc.
I have a recent model Tek digital color scope. It is an amazing instrument, especially when it comes to making quantitative measurements. Nevertheless, I have a love-hate relationship with the lil bugger. I still have a 465 as my primary trouble shooting scope on the bench. Even with a wonderful Tek digital scope, looking at irregular relatively fast events like pulses from radiation detectors can be problematic. In fact, troubleshooting any oddball, unexpected signal can be much harder with a digital scope than an old analog unit. Notice which scope is right at eye level on my bench, and which one sits at the back.
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From: Don To: Electronics_101@... Sent: Saturday, October 07, 2006 10:00 AM Subject: Re: [Electronics_101] Re: How limitting do you think a scope would be if it were limitted to 35 volts? The sampling rates on the low-end digital scopes and pc scopes has kept me away from them. for the $300 figure that was mentioned, you should be able to get a very good working tektronix 4xx series scope. The 465 is probably the most common, and easy to find a good working, clean unit. And as far as recording, there are camera setups just for that which are also easily obtained and used. you may wish to check out the Yahoo group "Tekscopes" for more info. Don ----- Original Message ----- From: rtstofer To: Electronics_101@... Sent: Saturday, October 07, 2006 8:39 AM Subject: [Electronics_101] Re: How limitting do you think a scope would be if it were limitted to 35 volts? --- In Electronics_101@..., "lcdpublishing" <lcdpublishing@...> wrote: > > Horses stopped, but I had no plans of pulling the trigger right away > as I don't have the money. > > I really don't understand that specification at all > though "50Msamples" > > Sounds like something that someone made up to represent something. > > Is it 50 million samples per second or something like that? > > As Stefan points out, the 50 Msps limits the frequencies that can be sampled. The absolute maximum signal that can be accurately sampled, according to the Shannon Sampling Theorem, is 1/2 of the sample frequency or about 25 MHz. And that requires that the signal be periodic. All bets are off for one shot signals. A square wave is composed of the fundamental frequency (let's say 100 kHz) and all of the odd harmonics clear up to daylight (a really high frequency). To get a decent leading edge, you probably need up through the 7th harmonic but I'm not going to do the math. So, for the 100 kHz signal you need to accurately display 700 kHz or sample at 1.4 MHz. No problem - the box samples far faster than that. However, when you get to frequencies above a very few MHz, the sampling rate isn't fast enough. At some point, that is a problem with all digital scopes. I have often thought about buying a PC scope. One of the reasons is that I like the idea of having a logic analyzer come along for the ride. And for those that worry about Linux versus Windows, Bitscope has the answer. FWIW, you can download the software and try it over the Internet by connecting to a device back at the factory. Anyway, I kind of like the Bitscope 310 (www.bitscope.com) but it only samples at 40 Msps. Richard |
