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Understanding WFM modulation

Your “B” is the stereo difference signal of broadcast FM stereo. It is placed at twice the pilot frequency so that it can be recovered by having the receiver lock onto the pilot signal and frequency-...
Kevin Reid AG6YO's user avatar
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11 votes
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How is FT8 modulated with both upper side band and FSK?

Remember that, theoretically speaking, a USB transmitter just takes a signal, shifts it up in frequency, and amplifies it. That means that if you take a 50Hz wide 8FSK signal centered at 1500 Hz, and ...
hobbs - KC2G's user avatar
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8 votes

How is FT8 modulated with both upper side band and FSK?

FT8 is just FSK. However, most legacy transceivers don't support direct digital to FSK modulation (and FSK to digital), but do support SSB modulation and demodulation (from and to audio). So these ...
hotpaw2's user avatar
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7 votes
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What are the technical reasons that there are no FM transmissions on the long, medium, or shortwave?

So, the bandwidth argument is the dominant one. You need to incorporate the full Carson Bandwidth in your channel spacing, not only the frequency deviation! As explained in my answer to your previous ...
Marcus Müller's user avatar
7 votes

What exactly is a "balanced modulator"?

To put it simply, a balanced modulator is a mixer which has two inputs and two outputs. The outputs are (input1 + input2) and (input1 - input2). So, if the inputs are 100kHz and 1kHz, the outputs are ...
Scott Earle's user avatar
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7 votes

Is double amplitude modulation useful?

One case where this might happen would be in the world of RF over fiber. In this technique, a radio-frequency signal is used to modulate an optical (usually infrared) signal for transmission over ...
hobbs - KC2G's user avatar
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7 votes
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Why can I hear Morse when not in CW mode?

You don't say where you are hearing the Morse code. You say "on the same channels", but don't specify where you are listening. If you send Morse code using a buzzer, then that generates an ...
Scott Earle's user avatar
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6 votes
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Is FM modulation still more resistant to noise when given the same bandwidth as an AM signal?

FM modulated radio is much more resistant to noise and can deliver better sound quality than AM radio. Under certain conditions, that is! Namely, additive noise, and a fading channel. or is this ...
Marcus Müller's user avatar
6 votes
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Is double amplitude modulation useful?

Sure, it's technically possible. But I can't think of a reason it would be useful. The resulting modulation would be more complicated to implement, and occupy more bandwidth, than ordinary AM. ...
Phil Frost - W8II's user avatar
6 votes

Practical limits to maintaining coherence in an HF channel

Doppler spreading is the change in received frequency from a distance transmitter due to the rise and fall of the ionosphere along the signal path. When the effective height of the ionosphere rises, ...
pidloop's user avatar
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6 votes
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Why do PSK modes have "bandwidth"?

Binary PSK with instantaneous phase shifts would be equivalent to multiplying a sine wave (the carrier) with a square wave with values at 1 or -1. When two signals are multiplied, this forms a ...
Phil Frost - W8II's user avatar
5 votes
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How does a transceiver work?

The article does in illustrate things rather nicely. Let's look at the receive side first: ...
Marcus Müller's user avatar
5 votes

How does rpitx generate arbitrary SSB data with a clock peripheral?

This is an incomplete and theoretical answer as I haven't looked at rpitx in particular. Rather than controlling the phase of a sine wave, my understanding is that with the Raspberry Pi "hack" the ...
Kevin Reid AG6YO's user avatar
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Air gapped digital communications mode on VHF?

Suitable, I suppose, though not especially efficient in terms of spectrum or power. Morse code was never really designed for machine demodulation, so unless you also need the ability to decode by ear, ...
Phil Frost - W8II's user avatar
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Why are carrier waves necessary?

The simplest answer is that the modulating signal, while it could be electromagnetic, will not have the desired propagation characteristics to carry out effective communications. By mixing the ...
Glenn W9IQ's user avatar
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5 votes

What exactly is a "balanced modulator"?

Partial answer, because I don't know the actual electronics theory, but I hope which will help make progress towards a complete answer: A balanced modulator is a mixer with a particular feature. ...
Kevin Reid AG6YO's user avatar
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5 votes

Would Orbital Angular Momentum (OAM) multiplexing work over HF bands?

This is a physicist level experiment, and its benefit over established methods disputed, and even Wikipedia says that it's performance benefit over MIMO are nonexistent to negligible. So, no. Not in ...
Marcus Müller's user avatar
5 votes

Can a phase-modulated voice radio transmission be received and heard properly by an "FM" radio?

Consider an unmodulated carrier. It has a phase that increases with time at some constant rate. The rate that phase increases is what we call the frequency. What if the frequency isn't constant, but a ...
Phil Frost - W8II's user avatar
4 votes
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How to identify type of modulation based on constellation diagram?

In general, any modulation that makes sense to plot on a constellation diagram could be described as a kind of QAM. However, we generally use the term QAM only for modulations that use both degrees of ...
Kevin Reid AG6YO's user avatar
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4 votes
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SSB Modulation and Differential Signaling

My current understanding from reading and looking at spectrum plots from SDR software is that the sound is modulated with the carrier, but only half the carrier wave. That's — not really accurate. A ...
Kevin Reid AG6YO's user avatar
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4 votes
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Video transmission between ATV and SSTV

So, a teaser first: With GNU Radio, you can transmit various DVB standards. Here's Alexandru Csete demoing his DVB-S2 transmission: As you can see from the FFT Plot generated by the flow graph in ...
Marcus Müller's user avatar
4 votes
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How does rpitx generate arbitrary SSB data with a clock peripheral?

SSB comprises both amplitude and phase components. For any instant, plot the baseband signal's Q (quadrature) and I (in-phase) components on the y-axis and x-axis, respectively. The amplitude is the ...
Brian K1LI's user avatar
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4 votes
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What is the FM-N mode?

FM-N stands for FM narrow band.This corresponds to a 2.5 kHz deviation. FM corresponds to a 5 kHz deviation. Most repeaters are still 5 kHz although with spectrum crowding, we will see more 2.5 kHz ...
Glenn W9IQ's user avatar
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4 votes

FSK or M-PSK for weak signal communications?

First, we should be clear that neither of these modulation methods allow signals below the noise floor to be decoded. The oft quoted -dB figures for FT-8 et al are really quoting the signal strength ...
Glenn W9IQ's user avatar
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4 votes

FSK or M-PSK for weak signal communications?

We'll have to lay down some rules for the comparison: For a fair comparison, the energy per bit in each scheme under consideration is constant. So, a "fair" alternative would be switching from 4-PSK ...
Phil Frost - W8II's user avatar
4 votes
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What are all the three letter codes for the different emission designators?

I found the answer in this article in the Wikipedia: types of radio emissions. From that article you can construct the different codes for different modes but there's a list of common examples: A3E: ...
Pablo Fernandez's user avatar
4 votes

How to decode a message with unknown bit rate in interstellar signal

An FSK signal which is the same symbol repeated is an unmodulated carrier, and like an unmodulated carrier, it contains no information. Making some assumptions about the bit shaping filter it might be ...
Phil Frost - W8II's user avatar
4 votes
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Peak envelope power should be 2:1 or 4:1 on meter?

Say the unmodulated carrier amplitude (voltage) is 1. At 100% modulation, the envelope will vary between amplitude 0 and 2. So at peak, the amplitude is twice an unmodulated carrier, but because power ...
Phil Frost - W8II's user avatar
4 votes
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Is it possible to have multiple people talking on the same radio channel at the same time?

if a number of these devices are transmitting on a specific channel, will a receiver walkie talkie be able to hear all the signals coming from the ground sensors? The exact result depends on the ...
Kevin Reid AG6YO's user avatar
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4 votes
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Both OOK and FSK used in the same transmission

Probably ease of detection, or using the known OOK signal as kind of a frequency-synchronization and rate-synchronization method. It's hard to tell – in low-power and least-cost electronics, the ...
Marcus Müller's user avatar

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