Godafoss FAQ

Display QRSS Transissions On the Go With the Godafoss App for iPad and iPhone.

To use this app, you need to feed the audio output from a your radio into the device. You can do this via one of several ways:

Set the device near the radio's speaker to pick up the audio. While easy to do, this is not ideal, as background noise can interfere with the audio, causing garbled decodes.
Plug headphones into the radio, and set one earphone near the mic. I find that with good quality headphones, this can work extremely well.
Use the microphone input jack of your device, by obtaining an appopriate cable and connecting the radio's line level output to the microphone input.
With the Camera Connection Kit, you can plug a USB sound input device into the iPad, and use a patch cable between it and the radio's audio output. This is by far the best solution.

You can use the volume indicator in the upper right corner to verify that audio is getting into your device, and that the volume level is appropriate.

If you are running iOS 7 or later, be sure to give the app permission to use the microphone. If you denied permission, you can always give it again by following these steps:

Open Settings app and go to "Privacy"
Select "Microphone" to get a list of all apps that have requested access to the microphone, and to control which apps have access to the microphone

If you're looking for a radio to use with the app, there are many different types to choose from. Take a look at our listing of radios to use with your app, to see several, along with some suggestions on how to choose a radio.

Godafoss displays a waterfall of the audio spectrum, letting you view QRSS, DFCW, FSKCW, and other slow transmission speed signals. You can place your device's microphone near the speaker or headphones of your radio to pick up the sound. Or, if you have a cable to directly connect them, that will work ever better.

A frequency axis is displayed to the right or bottom of the screen, depending on the direction the waterfall is running.

You can pan the range of audio frequencies by touching the screen and sliding with your finger, in the same direction as the frequency axis.

You can also pinch and zoom to adjust the span of frequencies displayed, up to a maximum of 0 to 20 kHz.

If you don't want to accidentally change the frequency range, tap the Lock button so it is highlighted. Panning and pinch/zoom will not affect the frequency range, so you don't accidentally change them.

When first started, Godafoss defaults to an FFT size of 4K, with a Hanning window. You can change these and other settings by tapping the Setup button, and a set of controls will appear:

The first two are sliders that set the minimum and maximum audio levels for the waterfall colors. Adjust these to get the best looking display for the signals of interest. Often you want a blue background, the minimum dB slider should first be adjusted for this. Then adjust the maximum slider for the strongest signal, often it is desired to make this red or pink, but you have the flexibility to set it how you wish.

The FFT size sets the number of sound samples used to compute the spectrum. Higher values provide better frequency resolution, but update more slowly, and can smear faster signals.

The window type controls what windowing function is applied to the data before the FFT is run. The window modifies the received audio data to reduce what is called "leakage" from non periodic signals. Leakage smears the signal over a wider frequency range. Experimentation will help you find he best settings. The following windows are available:

Rectangular
Hanning
Hamming
Tukey
Cosine
Lanczos
Blackman

Speedup allows multiple FFTs to be run on the same set of audio samples, shifted slightly in time, This can be useful when a larger FFT size is required, but the signal rate demands a faster update rate on the waterfall. A speedup of 1 means no speedup is applied, a speedup of 10 means that 10 FFTs are performed on each data sample.

Finally, you can change the direction the waterfall runs, to the left, right, up, or down.

Note that making changes to any of these settings only affects newly received audio, previously received audio already displayed on the waterfall is not affected.

You can take a screenshot of the waterfall by tapping on it three times. The screen will flash to let you know the picture has been taken, and it will be saved to your Saved Photos album. Then you can share your received signals with your friends.

Here are some details on directly connecting an audio line source to your iPad/iPhone/iPod Touch

Email your comments and questions to support@blackcatsystems.com

Last modified September 2, 2014