Skip to main content
9 votes

Device that plays only the audio component of a TV signal

In the U.S., analog TV VHF broadcasting ramped up around the early 1950's, but ended circa 2009-2011. In analog TV broadcast signals, the audio portion was transmitted as an FM subcarrier inside the ...
hotpaw2's user avatar
  • 13.4k
8 votes

How can quadrature mixing adjust the phase of all frequencies by the same amount? Can it be done in the digital domain?

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 ...
Phil Frost - W8II's user avatar
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 ...
Rodney Price's user avatar
6 votes
Accepted

Relative computational requirement for various digital modes?

Complexity of your question It's hard to make general statements here, because computational complexity is a property of the implementation of a receiver, which usually is a choice given the ...
Marcus Müller's user avatar
6 votes
Accepted

What exactly is the IF output on radios?

The 7300's "IF output" is a USB digital signal at 48kSPS, the same as the USB AF output (and you can only have one or the other at a given time). It places the dial frequency at an IF ...
hobbs - KC2G's user avatar
  • 12.5k
5 votes
Accepted

What is the current state of the art in CW filters?

I like your PLL approach, because it doesn't try to "recover the original signal from noise", but actually goes ahead and detects what you're actually interested in, the presence of a specific ...
Marcus Müller's user avatar
5 votes

Understanding how quadrature heterodyning captures information from negative frequencies

A negative frequency is just a positive frequency "in the opposite direction". Imagine I have a transparent wheel, which has a black disc inside of it at one point near the edge. Now imagine ...
hobbs - KC2G's user avatar
  • 12.5k
5 votes

What is Spectral Subtraction for noise reduction?

From https://link.springer.com/chapter/10.1007/978-3-322-92773-6_9 : Spectral subtraction is a method for restoration of the power or the magnitude spectrum of a signal observed in additive noise, ...
Mike Waters's user avatar
  • 8,033
5 votes
Accepted

Is the Nyquist rate independent of the power of the analog signal being digitized?

Completely independent. It is dependent on frequency only. The amplitude of the signal is only relevant when looking at the number of bits used (and the dynamic range). See here for more details.
Scott Earle's user avatar
  • 4,609
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 ...
Raul O.'s user avatar
  • 71
4 votes

What does a receiver's noise reduction function do?

What does this noise reduction do? That should depend on the device. Generally, it's to be assumed that it applies (analog and/or digital) signal processing to improve the perceived Signal-to-Noise ...
Marcus Müller's user avatar
4 votes
Accepted

Calculating the signal-to-noise ratio for CW (Morse Code) signals?

The answer can be fond in The ARRL Handbook 2019, Vol 3, although it's spreaded across different chapters. In short, SNR is typically calculated for the noise floor of 2500 Hz SSB signal. Particularly ...
Aleksander Alekseev - R2AUK's user avatar
4 votes

Understanding how quadrature heterodyning captures information from negative frequencies

Some quick definitions: a sinusoid with angular frequency $\omega$ and phase $\varphi$ at time $t$ is: $$ \cos(\omega t + \varphi ) $$ Now let's consider a scenario: we have an ideal mixer with an LO ...
Phil Frost - W8II's user avatar
4 votes

What is the current state of the art in CW filters?

Ringing in narrow filters may already have an answer here: https://dsp.stackexchange.com/questions/2170/why-do-i-see-ringing-in-the-output-of-a-digital-filter-with-a-narrow-transition "looking into ...
hotpaw2's user avatar
  • 13.4k
4 votes

Problem with sample rate

512 samples should take 256 microseconds, so your times look about right. The exact time it takes to execute those lines of code will depend on the rest of what your computer is busy with. And it's ...
tomnexus's user avatar
  • 11.4k
4 votes

Problem with sample rate

The RTL-SDR interfaces to your computer via USB. The USB interface and driver will buffer the data and send it to your software at the requested sample rate on average (baring underflow due to ...
hotpaw2's user avatar
  • 13.4k
3 votes
Accepted

Transmit filter for Amplitude-shift keying

A low-pass filter is one way to do it. Due to the interpolation done in the repeat block, you are representing a symbol with 1000 samples, and your sample rate is 2 million samples per second (the <...
Phil Frost - W8II's user avatar
3 votes
Accepted

How can quadrature mixing adjust the phase of all frequencies by the same amount? Can it be done in the digital domain?

An ideal frequency mixer simply multiplies its inputs. One input is the RF signal we wish to shift in frequency, and the other is the local oscillator (LO). For the moment, let's consider just an ...
Phil Frost - W8II's user avatar
3 votes

Can an ultra-wideband system transfer data at high speed without precise clock synchronization?

As hotpaw2 said, the thing is that while it looks like random noise, the actual UWB signal is correlated, in some specific way known to the receiver. I'll explain this using an example (keeping it ...
Marcus Müller's user avatar
3 votes

Can an ultra-wideband system transfer data at high speed without precise clock synchronization?

Even if all the transmitted UWB pulses are identical, and initially start at an unknown time, the pattern variations in the delta time between pulses could be used to code information. As with any ...
hotpaw2's user avatar
  • 13.4k
3 votes
Accepted

How narrow-band can a DVB-S2 signal be?

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 ...
nickhansenrf's user avatar
3 votes
Accepted

Using Satnogs' *.ogg files in GNU Radio flowgraphs

(This answer is from the perspective of GNU Radio programming; I'm not familiar with what SatNOGS is doing.) There are two problems to solve to use a given data file. First, you need to decode the ...
Kevin Reid AG6YO's user avatar
  • 24.7k
3 votes

Is the Nyquist rate independent of the power of the analog signal being digitized?

Theoretically, the rate is independant. In reality, exceeding certain power levels will cause real world digitizers to increase in non-linearities (clipping, saturation, thermal damage, and etc.), ...
hotpaw2's user avatar
  • 13.4k
3 votes
Accepted

Why does QPSK signal in GNU Radio shift away from my center frequency at higher frequencies?

Sounds like your SDR transmitter has a frequency error of 40-50 ppm (or, less likely, your transmitter is fine but your spectrum analyzer has the error). Try transmitting pure carrier, without ...
hobbs - KC2G's user avatar
  • 12.5k
3 votes

Why does beamforming bring more power to the received desired signal?

I don't understand the parameters of your equations. But ignoring the equations and answering the text of the question: beam forming depends on frequency and phase. If the phase of the output of two ...
hotpaw2's user avatar
  • 13.4k
2 votes
Accepted

Will the quantization noise be increased if the step level is increased?

Quantization noise is highly dependent on the signal source distribution and its amplitude, the number of ADC bits, and the use of dithering. For a high resolution ADC that is digitizing a full ...
Glenn W9IQ's user avatar
  • 18.6k
2 votes

Using Satnogs' *.ogg files in GNU Radio flowgraphs

You need to convert the .ogg file into something usable by the flowgraph. How to open satnogs iq.dat files covers a similar issue for IQ files. For example, an APT recording with ...
Mat's user avatar
  • 141
2 votes

How can quadrature mixing adjust the phase of all frequencies by the same amount? Can it be done in the digital domain?

...it looks like a "quadrature mixer" is really just two separate mixers, with one fed by an LO to which a [constant] phase delay has been applied relative to the other's LO. Yes ... and. Quadrature ...
Brian K1LI's user avatar
  • 7,878
2 votes
Accepted

Turning raw APT data into an image

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 ...
ElectroNeutrino's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible