I am contemplating calling this the XORgan.
I realise that this blog is the one that links from my web site. My other blog with more information on the WSPR Organ can be linked to from here.
On Sunday 25th of October I had an idea for generation of WSPR signals in a very simple KISS method using 2 Crystals and an XOR 74HC86 Mixer. By Sunday evening it was built.
It works really well, by the use of two identical Crystals and subtractive mixing any drift in those Crystals is cancelled resulting in an extremely stable Audio data stream.
A vast range of Crystal frequencies could be chosen I am using 10.0005MHz at this time, I wondered if this may be a problem for 10MHz reception but the frequency is far enough away from the Amateur allocation to cause no trouble. I have also used 8.192MHz.
The circuit shown is liable to be modified I didn't bother with an LPF after the mixer, the capacitor values were sufficient but I may try an RC LPF in there or after the Buffer. As the circuit stands the output is a very clean Sine Wave.
Notes:-
I have added an RC Audio LPF at the output during test, it cleans the sine wave of any miss shaping nicely.
The LED shown used as a Varicap is sketched upside down for me, I always use them reverse biassed, some use them forward biassed, in this way positive or negative keying can be utilised.
