How do use the Oscilloscope to look at the siganls in...??

[Rasengan]

How do you use the Oscilloscope to look at the siganls in frequency time domain?

is it possible?

I think I saw somewhere that u can build a circuit and use it with the oscilloscope that will let you look at the signals in frequency time domain.

Can anyone confirm????

Thanks

 

[Nigel Goodwin]

Re: How do use the Oscilloscope to look at the siganls in...

How do you use the Oscilloscope to look at the siganls in frequency time domain?

is it possible?

I think I saw somewhere that u can build a circuit and use it with the oscilloscope that will let you look at the signals in frequency time domain.

Can anyone confirm????

Thanks

It's called a 'spectrum analyser', they tend to be VERY expensive, there have been various add-on units for scopes over the years, but they aren't terribly cheap either - it's not a trivial thing to do!.

What sort of range are you looking for?.

 

[Someone Electro]

If you need for freqencys up to 44 kHz you can use you're computers sound card.

You simply conect it to youre "line in" port (or "mic" if you need more sesetivety) and get a freqency analizer software from the internet (there are a cuple of freware ones)
Use Yahoo or Google :wink:

 

[Rasengan]

At least 500MHZ+......definitely can't buy the oscilloscope so I was thinking if there is some sort of circuit that can help the oscilloscope see the signal in frequency time domain....would it be possible???

Thanks

 

[Rasengan]

Can I use the sound card thing with frequencies of up to 500MHZ+??

 

[Styx]

probably not, since sound card are design for the audible range: analogue =22kHz thus digital 44Khz,

snd card manufacturer would upp the manufacter cost my installing much higher bandwidth components than that.

Depending on the scope you could get a FFT module. you can get such modules for Tektronics scopes (only scopes I know about sorry) but they are still faily pricy.

If you have means to record the data from the scope (ie to a floppy) in comma separated variable (or similar means) you could post-compute the freq domain in Matlab or equiv software

 

[Nigel Goodwin]

At least 500MHZ+......definitely can't buy the oscilloscope so I was thinking if there is some sort of circuit that can help the oscilloscope see the signal in frequency time domain....would it be possible???

There have been various DIY spectrum analysers as add-on's for scopes, if you search on google you can probably find some? - but bear in mind, they are likely to be complicated, expensive to build, and difficult to align.

Amateur radio publications have published designs over the years, I seem to remember seeing one in Radio Communication a few years ago - stretched over a few months of issues.

What exactly are you wanting to do?.

BTW, a quick (very quick!) google produced this .

 

[Rasengan]

I'm just trying to learn more about the signals that flow through a modulator and the oscillator, so I wanted to look at those signal in frequency time domain.

I'm trying to get a clear picture of how the signals flow in a modulator, demodulator and the oscillator (i.e. in the transmitter and receiver).

I could do that using PSpice but then the signals in the receiver wouldn't be like the actual one that you get experimentally (you know with interference and noise).

 

[JimB]

At least 500MHZ+......definitely can't buy the oscilloscope so I was thinking if there is some sort of circuit that can help the oscilloscope see the signal in frequency time domain....would it be possible???

Thanks

A bit of terminology:

Time Domain, plotting the amplitude on the Y-axis, against time on the x-axis. Use an oscilloscope.

Frequency Domain, plotting the amplitude on the Y-axis, against frequency on the x-axis. Use a spectrum analyser.

Frequency Time Domain, a new one on me???

If you want to go probing around RF circuits to try and understand their operation, I suggest that you do not go to 500 Mhz+. You will affect the circuit you are investigating as soon as you put your hand near it, let alone touch it with a probe.
I suggest that you start off with circuits operating at less than 2 Mhz, layout and stray capacitance effects are a lot less down there.

PC sound card based software spectrum analysers are generally only good for audio frequencies.
Real RF spectrum analysers are expensive, even old second hand (good) ones will cost £500+

JimB

 

[samcheetah]

i think he means frequency domain and he is confusing it with time domain.

Rasengan i would suggest that you try out other simulation softwares with an underlying spice implementation like Multisim. you can simulate any type of circuit and you can also add noise and non-idealities in the system. as you only want to learn about frequency domain analysis this would be easier (and less expensive) then buying a spectrum analyser.

 

[checkmate]

There is such a thing as time-frequency domain, with a whole family of associated transforms such as STFT, WT etc. Essentially, the FT that you are all familiar with only applies to periodic stationary signals and hence not very useful most of the time.

Transforms are always digital processes, and let's assume you do not require real-time updates. So as long as you can capture the signal, you can do whatever transforms you want later. Hence, the main challenge lies in signal capture.

If you want resolutions of up to 500MHz, you need a whopping 1GHz ADC. If you still can't contemplate what kind of speeds you are looking at, that's 1Gb of data per second (assuming simple 8-bit ADC) or 200 times faster than the standard 5MIPS which the PIC16F877 provides (Assuming it does the capture and store operations all in a single instruction!). Even the fastest Intel processor would have problems achieving that kind of speeds, needless to say it exceeds the bandwidth of all buses available on your PC (Even your memory works at 400MHz only). Digital scopes and spectrum analyzers are expensive for a reason.

If you want something cheap, take a look at www.bitscope.com. They have designs that can reach 40 mega-samples per second. A far cry from your requirements, but already quite a challenge to DIY.

 

[Rasengan]

Thanks I'll try "samcheetah" suggestion, I didn't know u could add "noise and non-idealities in the system", yep I'll try this multism software.

I'm also looking for a book that can teach me how to analyze a whole circuit (RF transmitter and receiver) properly and what and which type of signals I need to look at to do whatever it needs to be done, like analyze the types of signals that can be obtained from the oscilloscope and why do I need to look at those signals.

In other words I kinda get lost when analyzing a circuit....I want to be like u guys!!!

Thanks everyone

 

[crust]

I think the user wants a spectrum analyzer. I use an HP RF spectrum analyzer, but for low frequency, I *really* like the one I got from Data Physics. I forgot the model but it is a PCMCIA card for a laptop and is only 4K. It does everything I could ask.

On some of the very high speed scopes they use the input to apply a charge to a CCD like array, then use a slower ADC to read it off. That allows them to capture transients and so on. My bench DSO is a 2GS/s and it has lots of capture bandwidth, but does not capture for very long at its highest speed (maybe 128K samples or something like that).

 

[TheOne]

If you have some time you could try to make a "poor man's spectrum analyzer" for a scope
http://www.nitehawk.com/rasmit/sa50.html

 

[samcheetah]

If you have some time you could try to make a "poor man's spectrum analyzer" for a scope
http://www.nitehawk.com/rasmit/sa50.html

nice link! lots of info