The filters in Rocky.
(Jan 25 2011)

Test method.

Linrad has a feature (F11 when playing a recorded file) that replaces the data from the hard disk by a swept signal about 0.2 dB below saturation. No noise is added so the noise floor is far below the noise that would be present if some hardware were connected. The file sim3.wav (60413996 bytes) can be downloaded here as a zipped file: (50307053 bytes) The file is produced by having Linrad play a file that was recorded with the WSE units using a single channel at 96 kHz.

The noise from the file and the simulated waveform were recorded in Linrads proprietary 18 bit format with .raw extension. The .raw to .wav converter of Linrad was used to produce sim3.wav in the standard 24 bit Microsoft PCM format.

Most SDR software can be tested at 500 kHz. Tests for Winrad, Linrad, WRplus, perseus.exe, WinradioG31DDC, SDRMAXIV, SpectraVue and SDR-RADIO are available here. A test with 192 kHz sampling speed for PowerSDR is available here.

This page has a test file for 96 kHz sampling speed. The highest speed currently accepted by Rocky.

Rocky 3.7

When the test file is played with Rocky, the screen may look like figure 1. It depends of course how the parameters in Rocky are set.

Fig 1. Rocky running sim3.wav.

The loudspeaker output from Rocky sounds like this: sim3-rocky.mp3 (735198 bytes.) The on-off keyed signal is 120 dB below the sweeping strong signal.

There are weak spurs, but they would be well below the noise floor with real hardware. There are however glitches in the output.

The details of the loudspeaker output are shown in figures 2 and 3 which are waterfall graphs produced by Linrad with sim3-rocky.mp3 as the input (before conversion to mp3).

Fig 2.The loudspeaker output from Rocky when running the test recording sim3.wav. This waterfall graph is produced by Linrad with the loudspeaker output from Rocky as the input.

Fig 3.The loudspeaker output from Rocky This the same as figure 2 at a 10 times higher waterfall speed.

The loudspeaker output of Rocky on an oscilloscope looks like figures 4 and 5 at different X-axis magnification.

Figs 4 and 5

The loudspeaker output from Rocky in the time domain when the signal sweeps across the filter.

The obvious problem with Rocky that is visible above is a glitch in the output. It could be caused by an inadequate computer (a Compaq 6510b was used for this test.)

The purpose of the test presented on this page is to find out whether filters are adequate. A few spurs are visible and audible in the test, but the levels are very low. The on-off keyed tone at -120 dBc is much stronger than the spurs so the spurs will not degrade the system performance when real hardware is connected.

The tested version of Rocky is version 3.7 downloaded as 936300 bytes on Jan 25 2011.

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