Thanks Andy, nice project.. maybe I should dig out the PIC programmer again... !

One suggestion for VLFers: A PIC doesn't cost a fortune. Build two of these generators, and clock them with the same source (GPSDO or OCXO). For the FSK simply flip between both generators. This has the *big* (cannot emphasize this enough..) advantage that if the signal is to weak to be seen as DFCW etc, we can still dig it out through a long FFT because each of the two carriers remains coherent, and can be coherently averaged as long as necessary (much longer than a single DFCW symbol). I noticed this on Stefan's signal today : With the very slow settings, all you see is a rounded hump in the spectrum because the signal isn't coherent. No chance to detect it for "DX" receivers.

Of course flipping the (FSK-) switch may cause a heavy click then (depending on the momentary phase shift between the two carriers) but I think a robust PA will survive this.

Have a nice sunday,
   Wolf .

Am 05.02.2011 19:57, schrieb Andy Talbot:

9kHz OPs may be interested in this DDS suitable for audio/ VLF using just a 16F628 PIC, , R-2R ladder and op-amp filter.   It can generate frequencies up to about 40kHz with typical DDS high resolution / frequency steps, (higher if you overclock the device)  offers two-tone FSK operation by toggling a single input line (ideal for DFCW),  The two frequencies are stored in non-volatile memory and are user-programmable from an RS232 interface using ASCII text based commands.

 

See www.g4jnt.com/PIC_DDS.zip for full details.

 

Andy

www.g4jnt.com