Questions tagged [sdr]

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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343 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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105 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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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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86 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
124 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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96 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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32 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
538 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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216 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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2answers
563 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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308 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
860 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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1k views

Is it possible to transmit and/or receive multiple types of signals at the same time?

Using an inexpensive SDR (such as the USRP or Per Vices Phi), I want to process two or more communication protocols at the same time (e.g. WiFi and GSM). Is it possible to Tx (or Rx) both at the same ...
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1k 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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3answers
5k 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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78 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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197 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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1answer
960 views

IQ sampling vs 2X f0 sampling for SDR

Are there any modulation schemes (or other situations) where sampling at or very near twice the carrier frequency would be better than IQ or quadrature sampling using a local oscillator at or near the ...
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3k 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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566 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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39 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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54 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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77 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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440 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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96 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
1k 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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396 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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4k 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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398 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
360 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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597 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
878 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
137 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 ...
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1answer
1k views

Splitting a Complex FIR Filter into Real Filters

I'm working on a software defined radio project on a PIC32 MCU. I'm using a CMX 973 quadrature frontend to provide I and Q. I'm independently low passing I and Q with carefully matched analog filters ...
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328 views

Detect FSK high/low bits in presence of noise with only simple processing

I'm currently in the process of writing DSP code, based on the amazing RTLSDR project, and using this as a vehicle to teach myself the basics of DSP (I have an extensive background in software ...
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1answer
1k views

Processing and plotting quadrature data in the frequency domain

Ok, so I recently started playing around with an SDR in an effort to challenge and educate myself. So, let's say the sampling rate (Fs) is 3MHz and of those we grab 3M samples. Now we are left with 3M ...