svensl

Pete, Thanks for the response. Since I was taking 2000s point for a record time length of 1e-6 (which corresponds to about 17 periods of the 17MHz signal), my sampling rate would be 2000/1e-6=2GHz. The picture is indeed the FM signal (17MHz), and the x-axis is just the samples. The wave displayed is not superimposed. Below, is the waveform at the beginning of the acquisition. Regards, Sven

The record time is not exactly the size of a period. It's more like 12.xxx. But I made sure when adding for example two record windows, that there is not discontinuity in the waveform. The trigger of the oscilloscope is just an edge trigger, at dc since the sine wave is centred around dc. Can you please clarify what you mean by "trying to remain synchronous". As for the funny behaviour of the waveform: I have a condenser microphone instead of a capacitor in the LC oscillator. Essentially, when excited with sound the capacitances changes, and I obtain a FM signal. Since the change in capacitance is small, I would not expect to see any change on the oscilloscope when exciting the microphone with a sine wave (The deviation in frequency of the FM signal around the carrier might only be 50kHz). And in fact I don

Pete, I ended up using the data acquisition in a loop which records the FM signal with constant time record. At each new iteration of the loop I move the start time by the time record. Thus, if the modulating sine wave is constant, I should be able to obtain a true representation of the FM signal, even if the osc. stops during streaming the internal buffer data to the PC. However, what I noticed is that after some iterations of the loop, the waveform starts "jittering" around. For example, it does not have an exact zero crossing anymore as it jumps up and down a bit. Once I stop the program and auto-setup everything, the waveform is stable again. Do you know what this might be caused by? I guess it must be due to the fact that with each iteration of the loop I move the start time by N*record_time, where N is the current loop iteration. But I don't know what exactly is causing this. Any ideas? Cheers, Sven

Yes, my circuit modulates a carrier wave (could be any frequency, but happens to be around 17MHz), with a slowly varying sine wave (could be a voice signal). At the moment I do not transmit the FM signal and use a receiver to receive and demodulate the signal to obtain the original modulating signal. But I will do that in the future. Currently, I want to do the demodulation on my PC as I want to test my modulating circuit to see how much of the original sine wave I can get back.

Thanks for your thoughts. There are many ways of extracting or rather demodulating the frequency modulated signal. In my case I am interested in the zero crossings of the sine wave (the 17Mhz signal). Each positive going zero crossing corresponds to a total phase change of 2PI. The modulating signal varies the phase of the carrier wave and thus varies the positive zero crossings of the signal. After acquiring the sine wave I would hard-limit it in Matlab to make it a pulse train. Then all that is left is to differentiate the signal and I should obtain the original 8kHz signal after low-pass filtering it. I will try to make it work with while loops, and/or, using programing. Thanks for your help. sven Ps. I will post any updates.

Again thanks for your valuable feedback. At the moment I only have access to that particular instrument but might be able to user a better one later. So for the sake of getting the job done assume we

Thanks for your post Pete. Sorry for not having given all the details. The waveform is a frequency modulated signal at about 17MHz. The oscilloscope is a 60Mhz, 200Msa/s. The modulating signal is a 8khz sine wave (slightly changing during data acquisition). Thus, to get decent information I would like to have 4 periods of the modulating signal = 500us. This is about 8500 periods of the 17MHz signal. For each of the 8500 periods I would like to have as many data points as possible, but a few hundred should suffice. Thus if we say 500 data points per period means 500 * 8500 = 4.25e6 points. All I want is the data points on the disk. I will then process them in Matlab. Is there a way of telling the oscilloscope to stream the data points continuously to the PC where they

Thanks for the link. I had a look at the manual for the osc. but could not find anything on how to continuously read data. It seems that the data acquisition stops when the osc. internal buffer is full. At least this is according to the manual. I am sure there is a way of reading data continuously from the oscilloscope. For example, when one wants to capture the signal obtained from a pressure sensor over a long period of time one would need to constantly quire the waveform. I just have no clue how to do that using Labview. Any ideas? Cheers, Sven

Hello all, I am having difficulties extracting data from an agilent 54621a oscilloscope and would appreciate if someone could help me. With the instrument drivers I downloaded from the NI website I can only acquire a maximum of 2000 data points of the signal that fits on the osc. screen. What I would like to do is capture a let's say 100 periods of a signal of which each period has 2000 data points. How can I accomplish this? Also, is there a way of continuously writing data from the osc to the computer, i.e. in vector form? Thanks Ps. I attached my current labview file. Download File:post-4408-1143459150.vi

I am new to Labview and have some questions on how to obtain a waveform from an oscilloscope connected via GPIB. Having installed the instrument drivers for the osc, I managed to obtain a captured waveform. However, this waveform is essentially just a screen shot (static) and has a limited number of points. I would like to record the waveform from the osc in continuous time (dynamically), meaning I would like to specify a start time, stop time, and interval time for which to take data points from the waveform that is constantly changing and save it to a file. Can anyone please suggest a way to do this? If so, please be very detailed as I am brand new to Labview. Thanks, svensl

I am new to Labview and have some questions on how to obtain a waveform from an oscilloscope connected via GPIB. Having installed the instrument drivers for the osc, I managed to obtain a captured waveform. However, this waveform is essentially just a screen shot (static) and has a limited number of points. I would like to record the waveform from the osc in continuous time (dynamically), meaning I would like to specify a start time, stop time, and interval time for which to take data points from the waveform that is constantly changing and save it to a file. Can anyone please suggest a way to do this? If so, please be very detailed as I am brand new to Labview. Thanks, svensl