Latest situation of the WSPR-RX
A while ago I did build my first 30m WSPR-RX to participate in the WSPR-challenge. I must admit it is very addictive! It did not took long before I was building my second WSPR-RX. This time a little bigger since the first one was too much miniature. Also I wanted to add some tweaks.
Temperature compensation
WSPR is a very small band signal. Actually it only covers 200 Hz on (30m) 10,138.70 MHz. When you build an x-tal oscillator for this receiver, it has to be quite stable to be able to hold the WSPR-RX between its lines. And the original design drifts. Too much for me. At some point I could read the rooms temperature from the drift of the decoded WSPR-signals.
In the original PA2OHH-design of this receiver there is an Negative temperature coefficient thermistor (NTC) with a varicap to compensate for frequency drift. I think Remco PA3FYM has left these parts out for simplicity but I wanted to build it back in.
Voltage regulated fine tuning
Furthermore to put the oscillator on frequency is a little challenging by itself. Since the original design almost never hit the 1500Hz band middle of the WSPR-band right away, you have to tune a little to get it right. Great, but how do you tune an oscillator that has no tuning options?
So I did build (with tips and hints from Remco PA3FYM) a voltage regulated add-on. As it turns out, you can re-engineer an 7805-voltage regulator to a variable regulator pretty easy. I did use this concept to design a voltage regulator for the whole design. I’m able to set the voltage between 11 to 14 volts which is enough to set the oscillator somewhere between 1400 and 1600Hz.
WSPR-challenge
In the meantime I am able to reach in the top 20 of the WSPR-challenge. Consequently to get into the top 10 seems very hard! I need all the (WSPR)-ears I can get. As a result I took everything I could find (including Roeland PA3MET‘s Sony ICF-SW7600G short wave radio) to create as many WSPR-receivers as I could in addition to the home made WSPR-RX’s. But it is still not enough to reach the top. I need to come up with another plan.
