WSPR idea

 Jay, W5OLF, has asked me to forward this:

"At the end of last year I designed the Retro-WSPR exciter around an Adafruit Trinket microcontroller and a 74HC4060 counter chip (see photos below).  Retro- I guess because it is at a single frequency and you rely on up/down conversion to get it to the WSPR band you wish.  It uses only one chip besides the microcontroller that is a 4.194304MHz oscillator and buffer, which is the RF out square-wave, and a counter that counts down to a 256Hz clock.  The 256Hz clock is input to an I/O pin ‘software interrupt’ of a very simple Python program on the Trinket.  This provides WSPR symbol timing and 2min timing by counting the beats of this clock.  I have never heard anyone proposing such a design in that the WSPR symbol time interval is 8192/12000; if we divide numerator and denominator by 32 we get 256/375.  Thus if we count 375 beats of a 256Hz clock it is one WSPR symbol time interval.  The next trick is that the clock at 4.194304MHz also is modulated with its mean frequency preserved - for long-term good timing - with the WSPR symbols by slightly changing the VCC to the counter chip (it takes very little voltage change to increase the frequency by 5Hz) using the A/D converter pin from the microcontroller.  This setup puts out a 0Hz drift WSPR signal with average low delta-t drift for months once the oscillator is adjusted to the correct parameters and the crystal ‘aged’; although, it is only the exciter. 

Now the next question is the up/down conversion circuitry which I have not experimented with personally but would use standard gilbert cell IC and transistor amplifiers and bandpass filtering.  If any of your readers of your blog want to experiment with doing this I can provide a unit or PCB and crystal for shipping postage only as well as emailing the software to them.  The I2C interface is brought out from the Trinket micro and can easily be used to initialize a SI5351 board to an up/down conversion frequency to feed into the mixer.  Please feel free to post this email on your blog.

73’s, Jay, W5OLF"