7
votes
Detecting signals using statistics
There is a range of possibilities, depending on what kind of signal you want to find. I'll start from easy and move up to hard. I'm assuming that you are using an FFT to get your spectra.
RFI. An ...
- 355
7
votes
Accepted
What is this burst transmission sequence across the entire band?
It's probably an ionosonde — sending out HF radio signals not to communicate but to measure the reflections and thereby determine the current characteristics of the ionosphere.
The signal is probably ...
- 25k
7
votes
Accepted
How does one know how a signal has been modulated
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 ...
- 17.3k
6
votes
Accepted
Help on identifying signal type and extract audio from a signal
It's narrow FM with a "voice scrambler". Before getting passed to the FM modulator the voice signal has its frequency components "inverted", in this case by being subtracted from a ...
- 13.2k
6
votes
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What is this weird interference/strange radio station?
Oceanographic radar, aka CODAR. It's used to measure ocean currents, wave heights and frequencies by the way the waves reflect RF.
- 13.2k
5
votes
Signal on various frequencies, about 2.5k bandwidth, sounds like a broken motor turning: What is it?
These are data transmissions using OFDM.
They are government or military point to point data links. I would expect that the data would be encrypted.
- 106
5
votes
Very odd and wide 30m signal. What is it?
If I read the instrumentation correctly, this is but 20 kHz; that's pretty wide for what I'd expect for Ham operation on HF. It's not "very wide" per se. (I'd define "wide" based on the ratio of ...
- 17.3k
5
votes
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Unidentified signals on FT8 frequencies
The fact that they align properly to the FT8 15-second period, and have 8 tones (the same as FT8) is a sign that these may be distorted FT8 signals, caused by AF harmonics in the transmitter or the ...
- 13.2k
5
votes
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What's the `Minimum signal duration` and `Minimum detectable signal duraion` of Ettus B210?
A SDR peripheral like the Ettus USRP B210 continuously digitizes the incoming RF and sends it to the attached computer. There are no gaps in its coverage — anything that is within the bandwidth is ...
- 25k
4
votes
Detecting signals using statistics
Well, this is a well-studied field (Radio Frequency Interference detection and mitigation). There are tons of literature about it.
The noise you receive is theoretically Additive White Gaussian Noise ...
- 71
4
votes
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Zigzag line on CB band
This reminds me of the "bad old days" of poorly-aligned or poorly-designed transmitters (usually CBs in the early 1980s in the UK), where the transmitter would start the PA before the PLL ...
- 4,669
3
votes
Local Relay with static
Could very well be someone who is bored and opens the repeater without actually transmitting anything useful. Happens on a lot of repeaters. You only need one person to do this to bother all users of ...
3
votes
Fourier transform of air breakdown impulse waveform
If you approximate the yellow trace as a rectangular function:
$$ \text{rect}(ax) $$
then the Fourier transform of this is:
$$ {1 \over |a|} \cdot \text{sinc}\left(\xi \over a\right )$$
Of course, a ...
- 52.4k
3
votes
Accepted
Open source RS41 decoder
You have to provide the -i option to invert the signal in order to decode it properly. The lowpass filter is not really required as this is a quite strong signal (...
- 46
3
votes
Receiving multiple signal
There's multiple way that multiple signals can be sent at the same time on the same frequency.
One is to have multiple antennas, where even though the antennas themselves can be omnidirectional, they ...
- 754
3
votes
Unknown signal on 446MHz LSB (possible RFI?)
From the wide spectrum screenshot it's evident your receiver is seriously overloaded. Note:
the signal around 445.982 which appears to be identical other than being "flipped", and a little ...
- 52.4k
3
votes
Unidentified signals on FT8 frequencies
Both marked signals follow an 8 tone MFSK pattern. The one on the left is about 125 hertz wide while the one on the right is about 100 hertz wide.
The signal on the left appears to follow the ...
- 18.6k
3
votes
Accepted
How to explain a frequency pic at 1.5 kHz?
display_qt is a GNU Radio example program. It does not display any actually existing electromagnetic signal but internally generates a 1500 Hz sinusoid.
The code ...
- 25k
3
votes
What is this pulsating signal?
That is almost certainly some kind of digital transmission.
Someone with suitable software could decode it and listen to it.
It could be voice or data. It's apparently too narrow for a video signal.
...
- 8,175
3
votes
Accepted
What is this interference?
These look so sharp and narrowband that I'd presume it's self-interference, i.e. parts of your SDR leaking into your receive path.
You need to look at the color scheme here: there's very strong signal ...
- 17.3k
2
votes
Accepted
Any ideas as to what I might be picking up on SDR?
"it might be European television broadcasting. What is your location?"
From the spectrum, it's neither video or DAB.
Looks like a spurious or other radiation from a nearby source.
Frank
- 106
2
votes
Accepted
What is this Morse code-like station?
Been probing around in your signal.
The longer "blips" definitely start with a tone (... with a region where phase is a linear function of time), but then it looks rather random.
So, likely, ...
- 17.3k
2
votes
Very odd and wide 30m signal. What is it?
I also didn't notice that box before, but it has the date as well, 2017-01-08 in it(YMD), a Sunday.
The center is 10.130, and at S7 that's fairly strong. Also I think the actual signal is 26khz wide ...
- 301
2
votes
Accepted
What is this odd data/screeching/fuzzy signal?
Welcome the land of QRM also known as man made noise.
I realize this came from the headphone jack, so it recorded as stereo. its really a mono signal, both channels have the same wave form. because ...
- 301
2
votes
Wireless signal strength explanation needed
First, the router power will be +20 or +22 dBm. Subtract a few dB on the way to the antenna, more if it's an internal antenna.
Second, the free space path loss will be at least 20 dB, from phone to ...
- 12.2k
2
votes
Wireless signal strength explanation needed
A Wi-Fi transmitter, like a lightbulb, throws out photons in a lot of directions. Only some of them will be captured by the receiver. Most will go elsewhere, eventually being absorbed by walls, ...
- 52.4k
2
votes
Accepted
Wireless signal strength explanation needed
I can think of a few reasons why your WiFi signal strength is 45 dB down from what your router's documentation suggests.
Your phone and antenna aren't calibrated. Your app makes signal strength ...
- 9,320
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