PSK and FSK are not the same thing. FSK uses two separate tones, only
one at a time, to represent logical 1s and 0s. In FSK the tone selected
is at full amplitude, and there is no information encoded in changes in
amplitude. As with CW and FM, FSK can use class C amplifiers.
PSK uses two phases of a single tone. The two phases are in quadrature (
90 degrees relative to each other ) and are transmitted at various
amplitudes. The two phases are called I and Q. A combination of the two
phases and amplitudes is sent simultaneously. Various types of PSK use
different numbers of possible amplitudes. The more amplitudes used the
greater the number of possible points mapped in the PSK "constellation".
If the constellation has four possible states, then two bits of data can
be represented by a single point of the constellation. In digital
microwave systems some forms of PSK may use an 8 X 8 or even larger
constellation. Some systems are adaptive and can automatically switch
between constellations with different numbers of possible states, fewer
states for poorer propagation conditions (and lower baud rates), and
more states (and faster baud rates) when the path is solid. Since the
amplitudes of the two phases of the tone are essential to define the
points in the constellation, linear amplifiers must be used.
The FSK input of a radio just switches the TX frequency between two
discreet tones. Only one at a time, and each at full amplitude.
I don't know the details of PSK31, but I do know you cannot send it just
by switching between two discreet tones of constant amplitude.
DE N6KB
Denton wrote:
> I am wondering about the fesability of tweeking my Omni VI's rtty, or fsk
> port for use on psk31. Has anyone done this?
> I am using the usual soundcard route for that mode presently.
>
>
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