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Software Defined Radio (SDR) is the implementation of radio receiver, detector and transmitter systems in software, as opposed to analog hardware or application-specific ICs. It usually uses a baseband sampled representation of the RF bandpass signals.

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Recovering data from mystery signal

I was scanning the airwaves using my RTL-SDR and found a signal being broadcast locally that I was able to receive. When I configure the SDR Console V3 software to NFM, I get the following audio. (Wav ...
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1answer
35 views

am I recording LTE uplink signals?

I have this app in my phone which tells me the LTE UL frequency and power: so I went with my SDR and measured the received signal at that frequency: Now, how can I be sure this is the transmitted ...
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26 views

How can I account for the 180 degree ambiguity in radio Direction of Arrival?

I'm working on a phase interferometry direction of arrival system for radio signals. It somewhat works for a range of 180 degrees (still very jumpy / imprecise), but due to only sampling at 2.4 ...
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1answer
45 views

why transmitting a long pulse its spectrum gets spread?

I'm transmitting an RF signal with a CC1101 at 440 MHz. This signal is a constant of 1, so the spectrum should be a delta. Using a SDR dongle, I've checked the spectrum and it's wider than a delta ...
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2answers
111 views

How can I align these two signals? Cross correlation isn't working properly

I have two radios sampling simultaneously, and I am trying to time-align their two signals (they will always start sampling at slightly different times with random delays due to hardware differences). ...
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1answer
51 views

How to undo dynamic Doppler effect by software?

I have a signal affected by Doppler effect. In general, the Doppler effect changes the scale of the time and frequency domains. So, to undo this phenomenon, I am using a sampling rate converter. Two ...
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1answer
120 views

Checking for VHF pulse with SDR and python

So I have a small NooElec Software Defined Radio and I've got it working well with my Raspberry Pi using GQRX as a controller and to visualize the SDR output. My goal though is to use a python script ...
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134 views

Software Defined Radio samples analysis using gnuradio and python

I'm trying to replicate what gnuradio is doing in "pure" python with a hackrf. Having mixed result, I decided to use the same data to compare the outputs I obtain. My gnuradio workflow is the ...
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79 views

Does anyone recognize this modulation?

I'm trying to extract the code of my garage remote, but i have some difficulty to find witch modulation has been used. At first I thought it was a simple digital modulation, but there is some strange ...
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44 views

USRP Gain Problem [GNURadio / Matlab]

I'm having a problem figuring out the noise floor of my USRP. Receiving on the USRP with no antenna attached with Matlabs USRP integration I get noise around 0-80 (magnitude of real portion) when I ...
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2answers
216 views

Help in understanding the IQ raw file format used by SDRs/GnuRadio [closed]

I apologise as I feel like I should know this off the top of my head. I will try to explain what I believe I know and then ask a simple question. The usual file format used in software defined radios ...
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1answer
70 views

How to get coordinates of complex RTL-SDR signal?

As I have already explained here (https://stackoverflow.com/questions/49358449/python-how-to-get-coordinates-of-complex-rtl-sdr-signal-peaks?noredirect=1#comment85722604_49358449), I need to find the ...
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1answer
38 views

Understanding unexpected i/q calculation on a downsampled signal

I am reading samples with an RTL-SDR, centered on an FM broadcast station: ...
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46 views

RTL-SDR data types

I am using pyrtlsdr to read samples from an RTL-SDR. As in the example on the page, I am getting samples with sdr.read_samples(x). The RTL-SDR returns 16 bits per ...
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1answer
61 views

FFT showing evenly spaced signals when tuned to ~56 MHz down to 25.680

I'm running GQRX on Mac OS X 10.11.6 hooked up to an RTL-SDR dongle. I noticed when I'm tuned anywhere between ~56 MHz on down to 25.680 MHz I see evenly spaced signals on the FFT. But when I tune ...
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1answer
221 views

Curved noise floor and ugly unexplained peaks after FFT

It has been so long since I studied this at University, so I'll better ask here if I'm doing something really wrong here. I'm using a USRP frontend for L1 band surveillance. I want a 20MHz bandwidth, ...
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1answer
56 views

Weird noise floor slope when capturing with USRP E310

I'm experiencing a weird effect on my captures. It may just be due to my bad dsp understanding. I'm using an E310 SDR platform to capture a multitone (4 carriers) signal: Fc = 150 MHz Bw = 286 KHz ...
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1answer
37 views

Multirate Signal processing for matching DAC of the SDR

I have been breaking my head for a long time. Please help with this..any input would be helpful! I am trying to implement a OFDM system using SDR (USRPN210 for Transmitter and USRP2 for receiver) ...
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127 views

Decimation and filtering in the frequency domain

I'm working on a Software Defined Radio project where I'd like to low-pass filter and decimate an analytical signal (IQ) sampled at 96ksps. Let's say the low-pass filter has a cutoff at 5kHz and I'd ...
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28 views

Signal view from two different receivers (of the same model)

I have two SDRs hooked up to two different computers, both radios tuned to the same frequency. They sample at 2Msps. What I would like to do is start up both (at 'about the same time'), and, after ...
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2answers
137 views

FM signal detection

I'm just playing around with cheap RTL based SDR dongle and I wanted to implement a simplistic FM radio receiver. I managed to get mono sound with no problem, however I decided to implement automatic ...
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1answer
81 views

How to calculate baudrate?

I'm going through this article https://www.elttam.com.au/blog/intro-sdr-and-rf-analysis/ and I find it hard to understand the following part: However, in our case we might want to transmit this ...
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27 views

Tx-Rx synchronisation to frequency changes

So I am part of an SDR project using gnu-radio and usrps where we are trying to set up a link between usrps. The ideal is similar to the DARPA spectrum challenge (https://...
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2answers
206 views

pyrtlsdr: Why is my output different than universal radio hacker?

I'm trying to build a script to do some signal processing from my RTLSDR. But, the bits I'm getting is not what I would expect. The preamble using 'Universal Radio Hacker' looks like this: But after ...
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106 views

Visualize the spectrum of a $433\textrm{ MHz}$ signal in MATLAB

I recorded a $433\textrm{ MHz}$ IQ signal with a SDR dongle as a .wav file and when I read it in MATLAB, I see the following: This is the code: ...
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1answer
126 views

Zeros inserted in QAM Constellation

I need to ask about insertion of Zero Symbols after QAM modulation in a OFDM system. Such that the 4 QAM has a constellation with 4 corner and 1 center symbol indicating zero. What advantages or ...
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3answers
2k views

What does correcting IQ do?

Some software (for example SDR Sharp) has a "Correct IQ" option. This is used to get rid of the DC spike in the middle of the display. What does this setting do to the signal? What is wrong with ...
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1answer
66 views

Spectrum Sensing HW

I am interested to use an existing hardware to perform a spectrum sensing/monitoring in the frequency range of 2.2–2.6 GHz. Taking into account that the 802.11ac channels are in the range of 2.4–2.5 ...
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2answers
475 views

IQ FM Demodulation of Wow and Flutter Signal in Software

Background: I have a recording device that exhibits Wow and Flutter, or periodic frequency deviation. I use this device to record a calibrated 3.15kHz test tone from a tape film to generate a .wav ...
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2answers
192 views

Adding a constant to a bandpass-signal in transmission

I do understand AM-DSB-SC and AM-DSB-TC, but can't see the point in adding a constant DC-offset of 2 in the upper part of this Simulink-model? Source
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1answer
109 views

Frequency-ratio at baseband IQ-mixing

I was wondering by what logic or mathematics the frequency-ration $$ \frac{f_{lo}}{f_s} $$ in the sine-functions comes into existence? Source
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2answers
911 views

Why do SDR receivers emit I/Q samples?

To my understanding hardware receivers for software-defined radio applications basically take the input signal, mix it with the tuning frequency to remove the carrier frequency and then sample the ...
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35 views

Taking care of 'splash' onto adjacent frequencies

I have a system that should identify activity on a frequency (say in a 5kHz range), and report the frequency. I have a problem with this system - the signal strength is sometimes wider than 5kHz, or ...
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36 views

Considerations when determining squelch

I asked this question recently. From the comments I learned that squelch is not a hard and fast thing, and that many considerations might go into determining a reasonable value, depending on use, the ...
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57 views

Coming up with a squelch value

I am building a scanning-type system. I have samples in $\textrm{dB}$ and I want to determine when to allow them through. I am trying to decide between allowing them through when they reach a ...
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1answer
272 views

Efficient way to get power levels from an SDR (RTL-SDR specifically)

At the moment I can step through the frequency band of interest and take samples to estimate relative power at various frequencies. But this is slow. Is it effective to center myself in the band of ...
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2answers
178 views

RTL-SDR units, $\textrm{dBm}$

I am using the Python rtlsdr library to get complex samples from my RTL-SDR USB stick. I am getting power by squaring the real and imaginary components of these ...
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2answers
101 views

Should I filter before calculating power, if I'm looking for relative changes in power?

I am building a "scanner" sort of program, which reads IQ samples from an rtl-sdr stick, and keeps track of the power on certain frequencies, in certain bands. I am interested in detecting activity ...
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64 views

When to use raw signal strength, vs. when to filter first

I am collecting I/Q samples from an RTL SDR dongle. I notice the rtl_power utility provided for Linux filters and does other processing, before reporting signal ...
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1answer
849 views

Possible to Derive Receive Signal Power from RSSI?

My Set-Up I am sending packets at a specific frequency and with a specific gain from one N-210 USRP to another of the same model. NOTE: I have the transmitting USRP connected to a series of ...
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1answer
2k views

Large spike at the center frequency when using Ettus X310

I am using the Ettus X310 SDR and GNU radio. On the GNU radio schema I have a standard UHD USRP source block connected to a GUI FFT sink - basically I'm just displaying the spectrum of the raw signal ...
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209 views

Understanding Baud or Symbol Rate

I'm trying to decode temperature data using an RTL-SDR from a La Crosse temperature sensor. It broadcasts on 433.92 MHz using amplitude shift keying (ASK). I've got the IQ data, then calculated the ...
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217 views

Moving signal power normalization

I am using matched filters using GNU Radio to extract from noise a CW Morse signal. The filter actually performs pretty well in various SNR environments. My problem is that the threshold upon I decide ...
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1answer
392 views

GQRX Frequency tuning

In GQRX (an GNURadio based RTL-SDR receiver) I have an FFT and waterfall display. When I tune to a local FM station (107.5MHz) I can hear strong, clear voice. But on FFT and waterfall display I can ...
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2answers
516 views

Sampling frequency lower than half of sampled signal frequency?

In GNURADIO when RTL-SDR Source block is placed there is a parameter Sample Rate (sps) and ...
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0answers
318 views

Short VHF pulse detection from SDR

I need to detect a short (10ms) VHF pulse that occurs every 1.5s at a specific frequency (e.g., 150.20 MHz). I have an SDR that support IQ sample rates up to 10MSPS but due to computing constraints 2....
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1answer
294 views

WFM SDR and Audio resolution

How does SDR resolution translate to audio resolution when using FM demodulation? For example: using a 8-bit/2.048 Mhz IQ stream, what is the maximum audio sample rate and bit depth that can be ...
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539 views

IQ imbalance on quadrature signal

Hi I am attempting to develop a reasonable IQ balance mechanism for a quadrature signal coming from a software defined radio.I can balance out the amplitude and phase differences at one frequency ...
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1answer
665 views

Sample rate changing audio pitch

I am using rtl-sdr at an adjustable sample rate to get stuff from a WBFM radio station. I then filter and demodulate it. When I sample at 2.4Msps, the sound is 'choppy'. I tied the sample rate to a ...
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1answer
112 views

Help on implementing an IIR filter

I am new to signal processing and and having difficulty understanding how to implement an IIR filter. The reference is athttp://www.dxatlas.com/rocky/Advanced.asp in the Band scope section. It ...