Tom` Blahovici (@tomb18)

Author of Win4K3Suite: Ham radio control application. Includes a software based panadapter. DSP code is handled by Mitov Signallab and c#.

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....
This is my software so it's up to me to code this...
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...

Re: Down sampling an iq signal

Reply posted 4 years ago (10/12/2018)
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...

Re: Down sampling an iq signal

Reply posted 4 years ago (10/05/2018)
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...

Down sampling an iq signal

New thread started 4 years ago
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...

Re: Removing DC Spike from an FFT

Reply posted 4 years ago (08/16/2018)
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...

Re: Removing DC Spike from an FFT

Reply posted 4 years ago (08/16/2018)
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...

Removing DC Spike from an FFT

New thread started 4 years ago
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. ...

Re: Upsampling of data

Reply posted 5 years ago (11/20/2017)
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...

Upsampling of data

New thread started 5 years ago
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...

Re: Downsampling from an FFT

Reply posted 5 years ago (08/24/2017)
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....

Re: Downsampling from an FFT

Reply posted 5 years ago (08/24/2017)
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...

Re: Downsampling from an FFT

Reply posted 5 years ago (08/24/2017)
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...

Re: Downsampling from an FFT

Reply posted 5 years ago (08/24/2017)
Great. That explains a lot! Now, the next question is interesting. Thanks, Tom 

Re: Downsampling from an FFT

Reply posted 5 years ago (08/23/2017)
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,...

Re: Downsampling from an FFT

Reply posted 5 years ago (08/23/2017)
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...

Downsampling from an FFT

New thread started 5 years ago
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...

Re: Decimation by 2

Reply posted 6 years ago (01/16/2017)
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...

Decimation by 2

New thread started 6 years ago
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....

Re: Downsampling from 2.0 MHz to 192kHz

Reply posted 6 years ago (10/27/2016)
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...

Re: Downsampling from 2.0 MHz to 192kHz

Reply posted 6 years ago (10/27/2016)
On Second though it is #2.  I want to isolate the 192kHz and then pass this on.

Re: Downsampling from 2.0 MHz to 192kHz

Reply posted 6 years ago (10/26/2016)
I there another way? I do have a set of fft bins.

Re: Downsampling from 2.0 MHz to 192kHz

Reply posted 6 years ago (10/26/2016)
,Thank you for this. Interesting article.Tom

Re: Downsampling from 2.0 MHz to 192kHz

Reply posted 6 years ago (10/26/2016)
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...

Re: Downsampling from 2.0 MHz to 192kHz

Reply posted 6 years ago (10/25/2016)
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...

Re: Downsampling from 2.0 MHz to 192kHz

Reply posted 6 years ago (10/25/2016)
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....

Downsampling from 2.0 MHz to 192kHz

New thread started 6 years ago
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...

Re: Removing DC and low frequency noise from a spectrum

Reply posted 6 years ago (10/23/2016)
Hi Thanks!No the 73 in ham radio lingo means Best Regards.How did you do that for the future?Thanks

Re: Removing DC and low frequency noise from a spectrum

Reply posted 6 years ago (10/23/2016)
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;...

Re: Removing DC and low frequency noise from a spectrum

Reply posted 6 years ago (10/22/2016)
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...

Re: Removing DC and low frequency noise from a spectrum

Reply posted 6 years ago (10/18/2016)
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....

Re: Removing DC and low frequency noise from a spectrum

Reply posted 6 years ago (10/18/2016)
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...

Re: Removing DC and low frequency noise from a spectrum

Reply posted 6 years ago (10/18/2016)
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...

Re: Removing DC and low frequency noise from a spectrum

Reply posted 6 years ago (10/18/2016)
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...

Re: Removing DC and low frequency noise from a spectrum

Reply posted 6 years ago (10/18/2016)
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...

Re: Removing DC and low frequency noise from a spectrum

Reply posted 6 years ago (10/18/2016)
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...

Re: Removal of DC Spike from quadrature receiver

Reply posted 6 years ago (08/14/2016)
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....

Removal of DC Spike from quadrature receiver

New thread started 6 years ago
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...

Re: Zero IF vs Low IF receivers

Reply posted 6 years ago (07/10/2016)
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...

Re: Zero IF vs Low IF receivers

Reply posted 6 years ago (07/10/2016)
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...

Zero IF vs Low IF receivers

New thread started 6 years ago
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...

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/19/2016)
Problem is solved...The SDRPlay device provides packets with different numbers of samples depending on the sampling rate.  Unfortunately, these packets are not...

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/19/2016)
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....

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/18/2016)
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...

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/18/2016)
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...

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/17/2016)
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....

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/17/2016)
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]...

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/16/2016)
Yes, I got that.  But why do the spectra look so different?

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/16/2016)
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...

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/16/2016)
Hi,Where do I reply here? Individually?  Or to my initial post?

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/16/2016)
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....

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/16/2016)
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....

Re: Newbie with questions about decimation for SDR

Reply posted 7 years ago (05/16/2016)
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....
Hi,I currently have software that will plot a spectrum from I and Q data obtained from a software defined radio.  The slowest sampling rate is 2msps.  This is...

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