Please see below reply from Joe Taylor on this very subject September last year, This is the guy who actually wrote this application (you might say from the Horse Mouth) and he said :-   On Mon, 7/9/09, Joe Taylor <[email protected]> wrote: From: Joe Taylor <[email protected]> Subject: Re: WSPR To: "M0FMT" <[email protected]> Date: Monday, 7 September, 2009, 1:47 PM Hi Peter, > Does your Software have a data output that gives a hi lo i.e 0,1 on the serial port other than the PTT Hi Lo? No. > If the software doesn't have this facility why not? Because there is no standard, nor even anything remotely approaching one, that would permit hard-keying an oscillator to produce continuous-phase 4-FSK with offset 1.465 Hz between tones. The WSPR program, as distributed, is essentially a sound card mode. With that said, it should be noted that a number of people have built special-purpose WSPR transmitters that implement the necessary 4-tone FSK capability in hardware.  Their keying is typically controlled from a  microprocessor, with the encoded message (sequence of tones) stored in ROM.     -- 73, Joe, K1JT 73 es GL petefmt --- On Wed, 7/4/10, Rik Strobbe <[email protected]> wrote: From: Rik Strobbe <[email protected]> Subject: RE: LF: WSPR without an SSB TRX ? To: "[email protected]" <[email protected]> Date: Wednesday, 7 April, 2010, 14:23 hello Chris, Jim, group, an alternative to a transverted would be a divider, let's say from 5MHz (from a HF tranceiver) to 500kHz. That would limit the hardware to some resistors an a single CMOS or TTL IC. I have written a small apllication that generates the appropriate WSPR audio signal based on the input frequency, output frequency and divider ratio. It worked fine for some local tests, but due to lack of I did no real "DX tests" so. But if anyone wants to try this route I will be happy to send the software. 73, Rik  ON7YD - OR7T ________________________________________ Van: [email protected] [[email protected]] namens James Moritz [[email protected]] Verzonden: woensdag 7 april 2010 15:09 Aan: [email protected] Onderwerp: Re: LF: WSPR without an SSB TRX ? Dear Chris, Andy, LF Group, What Andy suggests is fine for generating a WSPR signal, but receiving WSPR via the PIC might be a bit more difficult... But also at http://www.g4jnt.com/LFUpconv.pdf is Andy's simple phasing up-converter, which could be used to convert a PC audio output to 500kHz and be used in place of the VCO in your TX. Trawling through the Forum topics on the WSPRnet.org website (you might have to sign up to see all the material) will reveal many designs for homebrew HF WSPR beacons that could mostly be adapted to 500k. Cheers, Jim Moritz 73 de M0BMU