[Linrad] FM mode

[Michel <skynet.be; on7eh@xxxxxxxxxxxxxxxx>]

Hi all,

at the bottom of this page: http://users.skynet.be/on7eh/Linrad.htm
you'll find a screenshot of my first experimentation with the built-in
FM-mode in Linrad.

What surprised me at first were the many vertical lines in the high
resolution spectrum and baseband graphs within the FM-signal
bandwidth.

A look in my textbook refreshed my memory and provided the answer:
they indicate the spectral components that are symmetrical about the
carrier frequency and seperated by the modulation frequency.
Their amplitudes are determined by the Bessel function.
In the screenshot, the amplitude of the center frequency is some 10 dB
lower than the higher sidebands.

The audio quality of this distanced repeater was surprisingly good.
Linrad by means of its baseband filter offers an easy way of
experimenting with different filter settings and finding out what the
impact is on fidelity.

73,

Michel


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