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15 votes

How does IQ modulation work (intuitively)?

I think it's more intuitive if you unlearn some things first. Oscillation is not: $$ \cos(\omega t) $$ where $\omega$ is the angular frequency in radians per second, and $t$ is time. Rather, ...
Phil Frost - W8II's user avatar
7 votes

Fast TCP/IP radio modem on UHF band

As you might suspect, the data rate impacts the required RF bandwidth. Besides the data rate, the modulation method, encoding, packet overhead, duplexing, and other factors ultimately determine the ...
Glenn W9IQ's user avatar
  • 18.6k
6 votes
Accepted

Is there a difference between AFSK and FSK for AX.25/APRS USE?

My reading suggests that the advantage of AFSK is that the audio signal can be fed to any radio mike input. But if we ignore that, and assume a transmitter where the frequency can be controlled ...
Kevin Reid AG6YO's user avatar
  • 24.6k
5 votes

Is there a difference between AFSK and FSK for AX.25/APRS USE?

AFSK sent over a FM radio is very different to FSK, as explained in my blog post FM over FSK: FSK over FM is not FSK when you look at the over the air waveform. The spectrum is no longer two tones ...
David Rowe's user avatar
5 votes

How does IQ modulation work (intuitively)?

I believe a good point of view is the concept of orthogonality. This is clear under everybody's eyes when seen in physical space, take for instance a 2-dimension space, a plane. In the example above ...
carloc's user avatar
  • 183
4 votes

How does IQ modulation work (intuitively)?

First let's look at what happens in the case of a single mixer: simulate this circuit – Schematic created using CircuitLab We know that mixers produce sum and difference frequencies. That is to ...
Phil Frost - W8II's user avatar
4 votes
Accepted

SDR with the Raspberry Pi

Yes, with some important qualifications, you can "directly" generate SSB on the Raspberry Pi. The rpitx software you mention does that, and in combination with an RTL-SDR type dongle you would indeed ...
natevw - AF7TB's user avatar
4 votes
Accepted

How do I write a modem for DireWolf?

Actually, direwolf already supports higher data rates since 2017; it will use the G3RUH modem for a speed of 9600 or higher. As shipped it can be configured up to 40000 bps. But it's a mistake to ...
hobbs - KC2G's user avatar
  • 12.4k
4 votes
Accepted

What is "allied mode" with regards to PSK31?

That was just added by someone who's primary language probably isn't English. What they meant to say is "QPSK31, a mode that is related to PSK31, uses..." Other than that, the claim "it ...
Marcus Müller's user avatar
2 votes

What is "allied mode" with regards to PSK31?

In this case, "allied mode" can be replace with "associated mode" or "kindred mode." The phrase indicates that there is a relationship between the two modes, BPSK and ...
Brian K1LI's user avatar
  • 7,858
2 votes

Is there a difference between AFSK and FSK for AX.25/APRS USE?

FSK is a modulation where the instantaneous frequency corresponds to a binary baseband signal. Given: $x_m(t)$ is the baseband signal, perhaps a binary square wave taking values of -1 and 1, $f_c$ is ...
Phil Frost - W8II's user avatar
1 vote

How does IQ modulation work (intuitively)?

The concept of "negative frequency" deserves more attention. Real-world signals can be described in a number of ways to submit them to mathematical manipulation. This video shows two phasors ...
Brian K1LI's user avatar
  • 7,858
1 vote

Fast TCP/IP radio modem on UHF band

I know there's actually people working on a system for that band. It'll be SDR-based. There's no technical restriction that says you can't have a couple hundred kilobits per second in a couple ...
Marcus Müller's user avatar

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