Sunday, December 14, 2008

QS1R Selectivity, Audio Quality

Selecting the appropriate bandwidth is a two-step process. Clicking "FILT" or the bandwidth label (in the case of the picture: "4K") opens a new window from which you can select one of 16 preset bandwidths. Each can be tailor-made to your own liking. I was somewhat surprised to see that in AM mode, "4K" bandwidth is not 4 kHz, but 8! As long as you know, it's ok. Making a passband shift effect is easy enough; just adjust the slider on the bandwidth line. The bandwidth setting will reset to default if you press one of the bandwidth buttons on the bottom. Less elegant than the Perseus, but perfectly acceptable. I have no tools to measure the ultimate rejection of these bandwidths, so a comparison between the QS1R and the Perseus had to be made with ears only. I could not detect any difference between the two SDRs.

As we know, audio quality relies on a well designed AGC function. The QS1R GUI offers Long, Slow, Med, Fast AGC, or you can choose to turn it off. The settings can be adjusted the same way bandwidth can - at least in theory. The current GUI has the AGC options greyed out but the problem has been acknowledged by Cathy the GUI designer so I expect the option to be available soon. At present, even the "Long" AGC setting has a too short release time to cope with rapid fading. In such instances, "pumping" effects will be heard.

But audio quality and audio recovery is nonetheless superb. In situations with heavy interference, the weaker signal often appears more readable on the QS1R than on the Perseus. The difference is subtle, and the average listener may not detect it at all, but in some cases it could be the difference between hearing an ID or not. Audio recovery appears to be more "open" than the Perseus, making it easier to separate between several stations on the frequency.

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