I have downloaded a wave file of **SDRSharp SDR** that contains FM data I/Q samples for demodulation. The file attributes are sample rate=22050, samples=32 bit float. When i play it in SDRSharp, it demodulates FM signal and also shows frequency spectrum of the original signal i.e 50 Mhz. My question is how a wav file with 22050 sample rate can store 50 Mhz RF samples? If it is possible then it means one can have wav file of any frequency range stored at 48000 or 44100 sample rate? Can any one comment on this. _____________________________ Posted through www.DSPRelated.com
I/Q file frequency content
Started by ●June 19, 2014
Reply by ●June 19, 20142014-06-19
On 19.6.14 15:53, engrmasood2002 wrote:> I have downloaded a wave file of **SDRSharp SDR** that contains FM data I/Q > samples for demodulation. The file attributes are sample rate=22050, > samples=32 bit float. When i play it in SDRSharp, it demodulates FM signal > and also shows frequency spectrum of the original signal i.e 50 Mhz. My > question is how a wav file with 22050 sample rate can store 50 Mhz RF > samples? > If it is possible then it means one can have wav file of any frequency > range stored at 48000 or 44100 sample rate? Can any one comment on this. > > > _____________________________ > Posted through www.DSPRelated.comSDRSharp is just a piece of code written in C# and running on a Windows computer. There must be a piece of front-end hardware handling the radio frequency and its downconversion. The SDRSharp program knows which frequency it has requested from the front-end, and it seems that the information is stored in the wav file headers (in a way only SDRSharp knows). -- Tauno Voipio
Reply by ●June 19, 20142014-06-19
50 MHz sounds like a carrier frequency. If so, it has nothing to do with the frequency content (bandwidth), it's just the station. _____________________________ Posted through www.DSPRelated.com
Reply by ●June 19, 20142014-06-19
If you are interested in the theory, a keyword to search for is "complex baseband equivalent". The concept is quite central to modern radio engineering. The IQ signal is the "complex baseband equivalent" of a radio signal. That means, it is the positive frequency component, shifted to 0 Hz. The result is complex-valued, that's why two channels I and Q are needed. _____________________________ Posted through www.DSPRelated.com
Reply by ●June 19, 20142014-06-19
"engrmasood2002" <100558@dsprelated> writes:> I have downloaded a wave file of **SDRSharp SDR** that contains FM data I/Q > samples for demodulation. The file attributes are sample rate=22050, > samples=32 bit float. When i play it in SDRSharp, it demodulates FM signal > and also shows frequency spectrum of the original signal i.e 50 Mhz. My > question is how a wav file with 22050 sample rate can store 50 Mhz RF > samples? > If it is possible then it means one can have wav file of any frequency > range stored at 48000 or 44100 sample rate? Can any one comment on > this.I concur with mnentwig. 50 MHz was the original carrier frequency, not the actual sample rate. The signal had a < 22050 Hz bandwidth at the original 50 MHz carrier. Note also that since this is I/Q data, you have Fs bandwidth and not Fs/2. So if your sample rate is 22050 samples/second, then you have a bandwidth of 22050 Hz, not 11025 Hz as would be the case for real sampling. -- Randy Yates Digital Signal Labs http://www.digitalsignallabs.com
Reply by ●June 19, 20142014-06-19
>"engrmasood2002" <100558@dsprelated> writes: > >> I have downloaded a wave file of **SDRSharp SDR** that contains FM dataI/Q>> samples for demodulation. The file attributes are sample rate=22050, >> samples=32 bit float. When i play it in SDRSharp, it demodulates FMsignal>> and also shows frequency spectrum of the original signal i.e 50 Mhz. My >> question is how a wav file with 22050 sample rate can store 50 Mhz RF >> samples? >> If it is possible then it means one can have wav file of any frequency >> range stored at 48000 or 44100 sample rate? Can any one comment on >> this. > >I concur with mnentwig. 50 MHz was the original carrier frequency, not >the actual sample rate. The signal had a < 22050 Hz bandwidth at the >original 50 MHz carrier. > >Note also that since this is I/Q data, you have Fs bandwidth and not >Fs/2. So if your sample rate is 22050 samples/second, then you have a >bandwidth of 22050 Hz, not 11025 Hz as would be the case for real >sampling. >-- >Randy Yates >Digital Signal Labs >http://www.digitalsignallabs.com >i have downloaded other wav files not generated by SDRSharp but by Winrad i.e Winrad_20100823_142329Z_14181kHz.wav This wave file is for RF signal at 14.181 Mhz and still SDRSharps demodulates it and shows correct carrier frequency spectrum. Now we have two things based on what has been said in reply to my post. If 1. If SDRSharp puts header in its file then how come it's also showing correct frequency content of I/Q file generated by other program?. 2. Having said that I/Q is collection of samples of RF shifted to 0 hz then how one can know from I/Q data what frequency they represent at any instant? _____________________________ Posted through www.DSPRelated.com
Reply by ●June 19, 20142014-06-19
On 19.6.14 22:29, engrmasood2002 wrote:> > i have downloaded other wav files not generated by SDRSharp but by Winrad > i.e > Winrad_20100823_142329Z_14181kHz.wav > This wave file is for RF signal at 14.181 Mhz and still SDRSharps > demodulates it and shows correct carrier frequency spectrum. > Now we have two things based on what has been said in reply to my post. > If > 1. If SDRSharp puts header in its file then how come it's also showing > correct frequency content of I/Q file generated by other program?. > 2. Having said that I/Q is collection of samples of RF shifted to 0 hz then > how one can know from I/Q data what frequency they represent at any > instant?Have a look at the end of the file name: 14181kHz.wav It seems to be the SSB sample from DK3QN webpage. -- Tauno Voipio (OH2UG)
Reply by ●June 20, 20142014-06-20
>On 19.6.14 22:29, engrmasood2002 wrote: >> >> i have downloaded other wav files not generated by SDRSharp but byWinrad>> i.e >> Winrad_20100823_142329Z_14181kHz.wav >> This wave file is for RF signal at 14.181 Mhz and still SDRSharps >> demodulates it and shows correct carrier frequency spectrum. >> Now we have two things based on what has been said in reply to my post. >> If >> 1. If SDRSharp puts header in its file then how come it's also showing >> correct frequency content of I/Q file generated by other program?. >> 2. Having said that I/Q is collection of samples of RF shifted to 0 hzthen>> how one can know from I/Q data what frequency they represent at any >> instant? > > >Have a look at the end of the file name: 14181kHz.wav >It seems to be the SSB sample from DK3QN webpage. > >-- > >Tauno Voipio (OH2UG) >Does it mean that I/Q samples stored in wav file (22050 sample rate) can have samples of 14.18 Mhz? How my understanding is that Fs=22050 N=1024 (FFT Bin Size) ,therefore Bin 0= N * Fs/N=0
Reply by ●June 20, 20142014-06-20
On 20.6.14 12:21, engrmasood2002 wrote:>> On 19.6.14 22:29, engrmasood2002 wrote: >>> >>> i have downloaded other wav files not generated by SDRSharp but by > Winrad >>> i.e >>> Winrad_20100823_142329Z_14181kHz.wav >>> This wave file is for RF signal at 14.181 Mhz and still SDRSharps >>> demodulates it and shows correct carrier frequency spectrum. >>> Now we have two things based on what has been said in reply to my post. >>> If >>> 1. If SDRSharp puts header in its file then how come it's also showing >>> correct frequency content of I/Q file generated by other program?. >>> 2. Having said that I/Q is collection of samples of RF shifted to 0 hz > then >>> how one can know from I/Q data what frequency they represent at any >>> instant? >> >> >> Have a look at the end of the file name: 14181kHz.wav >> It seems to be the SSB sample from DK3QN webpage. >> >> -- >> >> Tauno Voipio (OH2UG) >> > > Does it mean that I/Q samples stored in wav file (22050 sample rate) > can have samples of 14.18 Mhz? > How my understanding is that > Fs=22050 N=1024 (FFT Bin Size) ,therefore > > Bin 0= N * Fs/N=0No. The samples are from a range of +/- 11025 Hz from the center frequency, which is in the DK3QN sample 14.181 MHz. The center frequency seems to be recorded in the file name. Forget the FFT, it is Nyquist that determines here. The frequency range is two-sided due to the I/Q two channel data. Each channel can transfer only frequencies from 0 to 11025 Hz. -- -TV
Reply by ●June 20, 20142014-06-20
On Thu, 19 Jun 2014 22:48:13 +0300, Tauno Voipio <tauno.voipio@notused.fi.invalid> wrote:>On 19.6.14 22:29, engrmasood2002 wrote: >> >> i have downloaded other wav files not generated by SDRSharp but by Winrad >> i.e >> Winrad_20100823_142329Z_14181kHz.wav >> This wave file is for RF signal at 14.181 Mhz and still SDRSharps >> demodulates it and shows correct carrier frequency spectrum. >> Now we have two things based on what has been said in reply to my post. >> If >> 1. If SDRSharp puts header in its file then how come it's also showing >> correct frequency content of I/Q file generated by other program?. >> 2. Having said that I/Q is collection of samples of RF shifted to 0 hz then >> how one can know from I/Q data what frequency they represent at any >> instant? > > >Have a look at the end of the file name: 14181kHz.wav >It seems to be the SSB sample from DK3QN webpage. >Another possibility is that these are not simple WAV files. The basic WAV format includes the sample rate and data format, but no "custom" stuff. However, WAV files are supposed to adhere to the Microsoft RIFF format, which allows for other data "chunks" to be included, properly labeled so that they can be skipped by software that doesn't understand them. Each chunk (including the WAV data) begins with a 4-char label, followed by a size DWORD, followed by the chunk contents. Then the next chunk label, size, and contents, etc. That makes it simple to skip over chunks that aren't understood. So it's certainly possible that the "secret" data is really there, readable only by SDRSharp and anything else that knows what to look for. Best regards, Bob Masta DAQARTA v7.60 Data AcQuisition And Real-Time Analysis www.daqarta.com Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusiq generator Science with your sound card!
