[Lf] GPS Locked PSK

[Andre Kesteloot]

Talbot Andrew wrote:

> I am now in a position to transmit GPS locked and timed PSK signals using
> the high power transmitter giving around 100mW ERP - at least it should be
> that power when the weather eventually stops raining.  A  lower power Tx is
> also available for microwatt ERP levels.
> Software driving the DDS module can generate any of these types of PSK data
> :
>
>         Pure binary code, specified as Hex or by its 1/0 sequence.
>         ASCII - non differentially coded in the Varicode alphabet as used
> for PSK31.
>         As above, but differentially coded to remove the phase ambiguity but
> giving 2* error rate.
>         CW representation,  where key down = 0 deg, key up = 180 deg
>             - Ideal for visual decoding on a time / phase plot but less
> efficient than varicode.
>
> Data rate can have any bit period that is an exact multiple of one second,
> and timed to UTC pulses.  For decoding purposes it may be convenient to
> define a time reference, such as the hour, where the data sequence starts;
> and also to define the start polarity at that point.
>
> Frequency using the GPS locked reference can be any exact multiple of 1/1024
> Hz (so all 1Hz values are possible)  but could have up to 20 degrees of
> phase jitter on it over a period of a few seconds.  The effect of this is to
> give 1Hz sidebands at a level of -40dB.    A more short term stable source
> can generate Caesium, MSF or TV sync locked frequencies that are based on
> 6.5536 MHz / 2^32, so exact Hz multiples are available every 25Hz.  I prefer
> not to have the Cs tube runing for extended periods as it has got to last a
> lifetime and I don't know how many hours are left in the tube.
>
> So if anyone is ready with vectorscopes, PSK demodulators etc.........
>
> Andy  G4JNT
>
> --