7

I can't dig up my source for this, but I'm pretty sure these spurs are just the result of rpitx using a fractional-N PLL (that isn't in any way optimized for phase noise) to generate a square wave. You get pulses of different (discrete) widths, which means you get spurs at predictable intervals. There isn't really anything you can do to make them go away, ...


6

The display is simple: Pass the incoming signal through two band-pass filters, one at the mark frequency and one at the space frequency. Use the two filters' output signals as the X and Y coordinates of the plot. (Since you are in the SDR domain:) Do as much as you want to make a nice-looking digital oscilloscope display of that signal. The simplest ...


6

Yes, you'll have to look at it. I can't go into detail about every possible modulation, because there's just too many. But typically, a look at the spectral representation gives you an idea of whether you're dealing with a straightforward single-carrier signal a spread-spectrum signal or a multicarrier signal. One place to see some examples is the Signal ...


6

Let's first start by developing some intuition of what a complex signal looks like. We can use GNU Radio to generate a signal that's just an unmodulated carrier, and then put that into a UI that will display the real and imaginary components over time: The result for 80 Hz is this: Notice how the real part is 90 degrees behind the imaginary part. If you ...


5

"IQ" refers to the practice of having two mixers with their oscillator phase 90 degrees apart, and then the digitization and processing of those two streams of data. One practical problem is in a superheterodyne receiver, the LO must be selected and the filters designed for the best image response. The problem can be understood intuitively like this: say ...


4

GNU Radio Companion (GRC) generates Python code that is something like this (not exact text). (Make sure you chose the "No GUI" option in GRC.) class my_block(gr.top_block): # ... def main(): tb = my_block() tb.run() if __name__ == '__main__': main() You can just import this as a module in your Python program (the if __name__ check will ...


4

Simply put, the LNA amplifies everything that comes into it. If you think about it, it's actually kind of amazing. It's dragging its output value up and down in response to nanosecond-by-nanosecond changes in its input, reproducing signals at every frequency up to its bandwidth limit. A good amplifier is as linear as possible (meaning its output is ...


4

Judging by this blog post from AI4SV and an inspection of the source code for fldigi (which supports such a scope in its RTTY mode), it's pretty simple — you just run the AF signal through two narrow filters at the mark and space frequencies (exactly as you would normally do when decoding RTTY), and then use the mark signal to drive the X axis and the space ...


4

The ARRL Handbook is a useful reference, but it's just that: a reference. It's not written as a text. It's useful for looking up forgotten details of stuff you almost mostly know, but it's not in a good form for learning things like electronics, antenna theory, an the like. A text aimed at self-study would be much more useful -- one written to be learned ...


4

While it is useful to have, NO single book contains everything that you want or need to know. Note that the ARRL Handbook is published every year, and each year contains different information. But even if you owned every Handbook that was ever published, inevitably something you want to know will still be missing. The last Handbook that I bought was ...


4

If the specific device is built around the Realtek RTL2832U chip, then the rtl-sdr driver software will be able to use it as an SDR. If it uses a different chip, then that driver will not work. It might still be possible to use that hardware, but would require writing new driver software and possibly reverse-engineering (the same as the original RTL-SDR ...


4

GQRX contains signal processing code, mostly executed in the shape of GNU Radio flow graphs, that convert the complex baseband representation of the RF signal that you get from your SDR device, to audio samples, which are then handed off to your operating system's sound system, which then hands them to the sound card, which converts them to analog, and ...


4

To just answer the literal question: I stands for Inphase and Q stands for quadrature. These are the two baseband signals you get when you mix the RF signal with a cosine of the carrier frequency, and with a 90° shifted version of that cosine, respectively (and properly low-pass filter afterwards). We call the first the inphase component, because it is ...


3

The answer is that the SDR hardware devices are all very different, so is the optimization quality of the SDR code. So one pretty much needs to calibrate for their specific setup: device, current method of connection, OS, and software running. I find network latency between the SDR hardware server and the software client to be one of the biggest variables, ...


3

You could call it a limitation of WebSDR, but WebSDR intends to give you demodulated audio, audio for listening to, which an IQ signal is not suitable for (even if the signal is audio-like as in SSB and CW, the 90° phase shift of the quadrature component will make for unpleasant listening). That said, you can take a SSB signal you've captured and turn it ...


3

I've heard that 2 days in the lab can save 2 hours of reading but in this case it turned out to be easy to test. It is the sample rate of the SDR which changes the bandwidth of the signal. Since I am using the PLUTO SDR I can't go below around 500ksps. So I tried with a symbol rate of 300 kbaud at a sample rate of 600k. Able to demod successfully. I asked ...


3

I found the solution to my problem. It was due to running my program using Python3, while as Marcus Muller stated in my other posting "GNU Radio 3.7 is not python3 compatible". So, using Python2.7 instead was the solution.


3

Short answer: No. The whole point of SDR is that the physical receiver doesn't care what the kind of signal is it's receiving as long is bandwidth-wise narrow enough and amplitude-wise not overdriving.


2

@Hadad, maybe you are not activating your pybombs prefix by running source setup_env.sh before using gnuradio? Documentation for details: https://wiki.gnuradio.org/index.php/InstallingGR#Using_PyBOMBS Once activated you should be able to import gnuradio within a python console without errors: $ python >>> import gnuradio


2

Is a panadapter hardware or software? If you use a hardware spectrum analyzer and a scope, it's hardware. If the panadapter is based on an SDR, then it requires both the SDR hardware and software. The difference between a waterfall and a panadapter is that the waterfall shows the spectrum analysis of a range of frequencies over time, which may include ...


2

I ended up figuring it out. I had to do three things: remove the Throttle block enable the "OK to Block" option in the audio sink ensure the amplitude of the sine wave is less than 1


2

I believe this blog post is trying to show the evolution of a good setup, rather than present a number of equally appropriate setups. You might want to first read How can I calculate the effects of an LNA, antenna gain, etc. on noise performance? Assuming the LNA is good enough to justify using, you want to: minimize losses between the LNA and the antenna,...


2

I see two main factors about the options in the blog. IMD Noise figure Option 4 is just option 2 but for a considerable cable length along with distortions and recommending to put the filter after the cable. Which is a good point for that case. Option 1 is the basis as the blog discusses the application of a filter. From there we have: a) Amplifier -> ...


2

It's difficult to give an exact number, because the overall latency involves at least: Processing of the signal on the given SDR Transferring data over USB 2.0 / USB 3.0 / PCIe (depending on what is used) Latencies on USB controllers on both SDR and PC (+ USB hubs, if used) Latency caused by other USB devices (keyboard, touchpad, webcam, ...) on the bus. ...


2

You might consider the following two books useful in learning more about radio design and the details of various circuits used in transceivers. These two are not equal in their coverage -- the first considers the electronics of radio technology and the second is more focused on the science and mathematics governing the application of various radio circuits. ...


2

The data is AM modulated on the 2.4 kHz subcarrier, with 256 different levels representing a single value from 0 to 255. It's a scanline every 1/2 second from the cameras with sync and telemetry data added to the beginning and end. Each line is 2080 data points (words) long, so it broadcasts at 4160 baud. The sync lines at the beginning let you know when a ...


2

It looks to me like you've put a lot of effort into tracking this down. I believe you are on the right track as far as the Pi creating a lot of broadband noise. But I'm wondering if you've tried putting the SDR on a extension USB cable so that you can move it as far from the Pi as possible? I've found that getting farther from a noise source helps a lot. ...


2

First of all, the properties of an antenna are far less important for receiving than transmitting. To receive anything at all, just about any piece of metal will do. That said, the lower the frequency (longer wavelength) you want to receive, the larger the antenna should be for it to work well. Once you get into the “HF” range (below 30 MHz, formally, but ...


2

However, depending on which options I choose on the Spectrum Analyzer, my measurements are different by up to 6-10 dB(!). Using a spectrum analyzer needs a bit of understanding what it does: it sweeps a filter across the spectrum and measures the power passing through that filter. I didn't know how to properly use a spectrum analyzer when I first did, and ...


2

A direct-sampling SDR doesn't require a mixer, which can simplify the design. Also, provided the receiver has sufficient dynamic range and processing power, a direct-sampling receiver can monitor all the bands at once. On the other hand, a direct-sampling SDR must have an ADC and DAC at a sample rate above twice the maximum frequency. So for an SDR that ...


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