#qtradio

If you have some time, have a listen to Matthew Pray's podcasts on a number of interesting subjects. Number 61 is devoted to Skywave Linux. Part one is focused on installation and getting audio going. Part two focuses on using the applications - QtRadio, internet SDR servers, etc. If you have some experience to share, drop him a line.

A Skywave Linux user recently had a question about connecting the audio stream from QtRadio into Fldigi. It is not quite as simple as it seems, though it seems to work out-of-the-box on a lot of computers. On a lot of laptops, especially, speaker audio couples into the microphone and digimode reception is possible in Fldigi. A more effective way to operate is directing QtRadio's output into the Pulseaudio processing chain and also connecting Fldigi to that chain's "monitor". For example, look in QtRadio's audio settings and note that there's a choice for the equalizer-dynamics-limiter LADSPA modules. Feed audio into that and you can hear the receiver output. Next, start Fldigi and make sure its audio input is set to Pulse. Lastly, the critical connection is made in PaPrefs - where you route sound within Pulseaudio. Connect the "recording" audio for Fldigi to the same processing chain as the output from QtRadio. When that connection is made, signals from the radio should appear on the Fldigi waterfall, with no local noises picked up by the microphone. That's all there is to it. Simple as pi, right?

Skywave Linux 1.4 will have it when it comes out, along with similar WBFM support in CudaSDR.

RTL-SDR device running in QtRadio. Skywave Linux 1.3 is posted, with upgrades and tweaks. This image shows wideband FM on the 80 khz filter. Any chance of hacking the code and adding a 200 kHz filter?

Version 1.2 has zram enabled plus other core system improvements for users on modest hardware.

CPU load is reasonable in the test machines. Dual core 2GHz speed, 4gb RAM, and an old hard drive is entirely sufficient, it seems. The app demanding the most, not surprisingly, is CubicSDR, since it does DSP on board, and on large chunks of spectrum. QtRadio does its job and the machine stays cool as a cucumber.

CubicSDR receiving two FM stations and QtRadio tuning a remote HF radio server.

http://skywavelinux.com