Antenna adapter-Raspberry Pi, weak signals (WSPR) and filter

Using the case of an old "HUMAX" digital decoder I placed, inside, an antenna adapter and a Raspberry Pi - Model B - 512 MB - used to transmit WSPR. The adapter consists of a coil with ferrite inside, a 12 position switch and a variable capacitor for further adjustments. For the signal transmitted in WSPR on 40 meters, I use the GPIO which supplies about 10 mW of power (+10 dBm), a low pass filter 7 Mhz (better described here)  and this antenna homemade. At the beginning of 2023, I inserted an amplifier with a simple 2N2222 transistor, thus bringing the output power to about 100 mW (+20 dBm) powered directly from the GPIO pin of the Raspberry (5 Volts). A.P.R.S. location transmitted with Perl script. I then added a filter for 20 meters and, with manual switching - 100 mW amplifier signal output - I can also transmit at 14,095.6 Mhz.

•   Special thanks to Giovanni IT9TZZ.

 

 

 

 

 

 

 

 

... high brightness LED when GPIO transmit.

 

 

This device (radio frequency probe) allows you to measure the radio frequency voltage present in a circuit. In this way one can know the magnitude of the signal produced by an oscillator or a transmitter.

 

  

• Measurement after the filter.
  

 

• Measurement directly from the GPIO

 

 

...with amplifier 100 mW 💪

 

 

... results with 10 mW

 

... results with 100 mW 

 

 

 

... results with 100 mW  on 20 meters