Tom` Blahovici (@tomb18)
I am writing software to collect data from several different Software defined radios. Typically they provide a packet of data that contains Real and Imaginary...
Well, it turns out that exactly the same number of packets leave the DSP code and arrive in the audio code. In fact if I send the audio to a wav file and play...
Hi,Yes that will probably work.I did do some benchmarks with timers and I found that on average, the audio routine was two packets short over a 10 second period....
The input rate is defined by the radio and the output by the Windows operating system. I think the complicated part here is to calculate how much the rate is off. ...
You are correct. In fact, there are several seconds in addition to the 5 where the sound is perfect so I do believe that it is an underrun situation.
Hi,I am collecting IQ samples from a software defined radio and decimating them to a rate of 192kHz. I then pass the buffers to an audio component (part of a library...
Well, I have solved the whole down sampling issues that have perplexed me for some time.As I mentioned in my first post, I didn't see any obvious aliasing because...
Hi,I passed this question on to a friend who is an expert in DSP and he pointed out what the effect of aliasing has on the resulting spectrum.When I downsampled...
Forgive my newbie questions. I always thought that to down simple a signal you first should do a low pass filter and then Dow sample to prevent any aliasing. So...
Hi,When you are talking about a block, what exactly do you mean?The SDR delivers 200 i samples and 200 q samples in each callback. I continue acquiring samples...
Hi,It sure looks that way. I just did this again like you suggested and I got-0.000000000000058120175339126945I guess that qualifies as extremely low...
I asked this question before but I thought I would rephrase is a bit with a little more background.I have a software defined radio that provides a quadrature signal. ...
Thanks for all the answers. yes linear interpolation is fine. I guess what through me off was the cases like starting with 2047 samples and interpolating to 2048....I...
Hi,I need to be able to convert a set of data composed of X samples with amplitude Y to a new set of data.The original data has anywhere from 1024 samples to 2048...
Ok. You are right of course! I was thinking of what the result was after further processing when converting the output for plotting.Perfect! Much thanks here....
Ok. But where are the negative frequencies?When I run the FFT I receive as output an array of 16384 values. The values from bin 0 to 8191 are the frequencies...
Hi,This seems real simple! Let's see if I got this straight.1) I zero out frequencies above the frequencies of interest.2) I perform the iFFT.3) I keep 3 samples...
I am not that knowledgeable in DSP but trying to learn.Perhaps knowing how my tools work will help. My iFFT tool will take an array of complex numbers.For example,...
Thanks. My understanding is that I can do the "trick". This is where I am having issues.First of all, there are 16384 samples since this is a complex FFT and...
I would like to down sample a signal from it's original sampling rate of 2,000,000 samples per second to 48,000 (or 44100) starting from the output of an #FFT. This...
Well I have made progress. When I use a device that is sampling at 2,000,000 samples a second I need to downconvert it to 48000 samples per second to get it to...
HiI
have a question concerning getting a virtual audio cable output in a program I wrote. A virtual audio cable output is an audio stream where the left channel...
Lots of good comments here. Thanks. As to signal content between 192 and 384kHz there will be potentially quite a bit so then a simple filter will not do.This...
I have a need to downsample a signal that is at 384 kHz down to 192kHz. I have read that you first apply an FIR filter then you throw away 1 out of every 2 samples....
I do get the idea of rational vs non-rational downsampling. I've been reading everything I can about it. Nonetheless it is not an easy field for a non-DSP professional...
The IQ signal is centered at zero hz. It is obtained by sampling the rf space around a tuned frequency. So I guess its both. #1 is done in the sdr, but what i...
No. I do not want to demodilate the signal. I want to pass this signal on to another application that requires a wide bandwidth so that it can scan a spectrum for...
I think it's best to explain this a little more. I have a software defined radio that samples at 2mhz and higher. I do not have access to a lower sampling rate....
I would like to downsample a signal (#SDR) from 2MHz to 192kHz. I understand the general principle when you go from let's say 1.92MHz to 192 KHz but what happens...
Success. While I do not know why the above example didn't work this one, based on an IIR filter does!!double wt_i = 0;
double prev_wt_i = 0;
double alpha = 0.988;...
Well I investigated all possibilities and HDSDR also shows the spike at -70dB. In HDSDR, if I then enable DC correction it disappears as it should. However in...
Ok, this is probably where my issue is. The offset was about 15dB above the baseline and the baseline was - 90dBm or even more. But the scales are all relative....
HiI think I may have found where I am having an issue. I compared my spectrum to that of HDSDR, and I found that there was no spike at DC as in my setup even if...
Hi,In my code I have access to the I and Q samples independently at this point. So, I have done what you suggested with independent I and Q corrections for the...
Hi,This is perfect. Only question is if you receive the I and Q samples independently which is the case for me. My limited DSP knowledge suggests that you could...
I have tried out this idea and it does work, but it is dependent on the average signal level over the whole spectrum. So if there are no signals, it works pretty...
Hi this is interesting but I don't think I quite follow. So, for my first block, I start with .05, subtract this from each sample, and then average the block. How...
In a previous post, I asked about removing a DC spike from a spectrum generated by a quadrature receiver. I have been able to remove the DC spike but the spike...
Thanks for the suggestions.I have however determined that subtracting the mean does reduced the central spike a bit. It lowers it from a height of 15dbm to 10dbm....
Hello,I have an application that plots a spectrum originating from a software defined radio. I have read a number of articles of how to remove the spike at DC...
Hi,Looks excellent. Much thanks for this.In any case I just found out the reason for not seeing anything on the spectrum in low IF mode.It turns out that the SDR...
HiGood explanations for the zero vs low IF. But I still don't get the idea of the processing. The SDR I am using at zero IF has it's center frequency tuned to...
HI,I am having some conceptual difficulty understanding how one an process data from a low IF recever. Currently I am using an #SDR which has a "zero IF" mode which...
Hi,Ok, just to be clear: The SDRPlay device has a minimum sampling rate of 2 msps. I start with this and then perform 16384 smaple FFT's. This gives a resolution...
Hi, been away on a fishing trip with no internet.Ok, so to get this right, I am doing a 16384 point FFT on the 2msps signal and then doing a 16384 point FFT on...
Ok, so how can i tell if antialiasing is occurring? I am using a 64 order FIR filter. The signals appear the same as far as I can tell. And the FFT duration will...
Hi, I am collecting samples at a rate of 2,000,000 per second from a software defined radio (#SDR). I am plotting the output of a 16384 point FFT and observing...
Problem is solved...The SDRPlay device provides packets with different numbers of samples depending on the sampling rate. Unfortunately, these packets are not...
Hi,I'm using the SDRPlay device. It has a range of 100 kHz to 2 gHz with a bandwidth of 8 MHz. One of the least expensive "high end" SDRs.As to a WAV file, I can't....
Hi,Yes I am seeing that the -128 KHz to +128 kHz is pretty well identical to the filter output.Where I see the issue is that the 256kHz downsampled spectrum looks...
Hi, Thanks.Here is a picture of the filters response. filter-response.jpgShould this be set at 256000 or 128kHz? I tried both and it makes no difference to the...
Hi,It's up to me to label the axis., The software will not do this automatically and I didn't bother at this time since it will depend on the tuning of the radio....
Hi,Ok, Thanks.[1] Here is the original showing -2.048MHz to +2.048MHz (it's a quadrature signal) 2msps.jpg[2] Here is the 2msps with the FIR filter 2msps-with-filter.jpg[3]...
Ok, I have it all working....sort of.For starters I just wanted to get things going simply. So I am using an FIR filter with 64 taps and a cut off frequency of...
Thanks for all the answers. I Guess, there is no absolute rule here and I have to play. So I started with 32 taps (Mitov has an FIR designer) without downsampling....
Thanks for all the answers. I Guess, there is no absolute rule here and I have to play. So I started with 32 taps (Mitov has an FIR designer) without downsampling....
Thanks for all the answers. I Guess, there is no absolute rule here and I have to play. So I started with 32 taps (Mitov has an FIR designer) without downsampling....
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