Amateur Radio Stack Exchange
Amateur Radio Stack Exchange

Questions tagged [modem]

Use this tag whenever the subject includes Modulation and Demodulation of in-channel digital signals.

Use this tag whenever the subject includes Modulation and Demodulation of digital signals.

This may include AFSK like in RTTY, or more exotic methods like AX.25 packet radio.

7 questions
9
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7 answers

How does IQ modulation work (intuitively)?

I'm trying to get my head around IQ modulation. What I understand so far is that each of the I and Q branches of the mixer produce two sidebands with the same frequency components, but in the Q branch, these sidebands have opposite phase to each…
John B
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7
votes
3 answers

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

APRS uses the AX.25 protocol which assumes the Bell 202 AFSK modulation scheme to generate the actual radio signal. Is there any reason the same signal can't be generated directly with FSK without going through the audio frequencies? My reading…
jgalak
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4
votes
1 answer

SDR with the Raspberry Pi

I wanted to explore digital modes by connecting a Raspberry Pi via audio cables to a transceiver. However, I realized that thanks to the clock generator, the raspberry pi can produce RF signals directly. Adding a square to sine wave converter, a…
Edgar H
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3
votes
1 answer

How do I write a modem for DireWolf?

I was looking at the selection of modem bauds for DireWolf and it seems the highest baud modem is 9600 baud, and I am using a sound card that can reach 48 khz. Is there any way that I can write a modem for DireWolf to utilize the 48 khz capabilities…
Steve Mucci
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2
votes
2 answers

Fast TCP/IP radio modem on UHF band

I'm interested if it is possible to have a data radio modem that works on the UHF band 400MHz for TCP/IP communication. What I have in mind is something similar to a router, but using UHF band for more range. The problem that I come across is that…
Synaps3
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1
vote
1 answer

FSK Rx sensitivity with different deviations

I used an RF generator transmitting FSK packets with a datarate of 50 kbps. The deviation was 12.5 kHz. With this combination of datarate and deviation the modulation index is 0.5. I found that my device undertest had an Rx sensitivity of ~102 dBm.…
Mikey
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0
votes
2 answers

What is "allied mode" with regards to PSK31?

Wikipedia says: Colloquial usage of the term 'PSK31' in amateur radio usually implies the use of the most commonly used variant of PSK31: binary phase shift keying (BPSK). BPSK uses no error control, but an allied mode, QPSK31 quadrature phase…
Xunie
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