With the 2n3819 JFET fitted, it was time to test the receiver once again.
PSK31 on the 20m band operates on USB. The dial frequency is 14.070 MHz.
The shack transceiver was tuned to 14.070 MHz. The tip of a short coax cable, from it’s antenna socket, was held close to the PSK31 board’s local oscillator circuit. Key devices here are IC1 and Xtal CR3, shown in the photo and circuit diagram below. A low frequency audio tone was heard from the shack tranceiver.
The frequency of the 14MHz local oscillator on the PSK31 board was adjusted with C11. The aim here was to make the transceiver’s audio tone drop in frequency, toward zero Hertz. As the audio tone approaches zero Hertz it will no longer be heard. This ‘zero-beat’ frequency confirmed that the PSK31 board oscillator matched the 14.070 MHz displayed on the transceiver.
With tuning complete the shack antenna was connected to the PSK31 board coax cable and SO239 plug. The audio cable was connected between the board’s 3.5mm jack-socket, SK1, and the computer mic input.
PSK31 Digital Mode Software
The DIGIPAN software was already installed on the shack Windows PC. However some settings required adjustment. With the mode set to BPSK31 and Receive ( RX) selected, the computer mic volume was lowered to reduce the noise on the DIGIPAN screen ( Yellow colour). With a lower audio input level the display produced a mosty blue background. Now the BPSK31 signals were clearly visible as yellow vertical lines (see screen shot below)
[Screen captured in MM0PYR shack on 10 April 2014]
The strong signals received were error free. Some of the weaker stations however contained errors in the message received. This is likely due to the lower signal to noise ratio for weaker stations. Further testing in better conditions on the 20m band are required to confirm this.
From the DIGIPAN screen-shot it can be seen that received stations included YU7AS in Serbia, distance 2,000 km (1,300 miles) , OE1TRB in Austria, 1,600km (1,000 miles) and DG0DE , Germany, 1,400km (860 miles).
Well done MM6LKG (Arthur), for getting the RSGB PSK31 Centenary receiver built and working, completing this project for the Intermediate License practical assesment.
Now that the board is complete and working it only remains to tidy the project up. Fitting the board, battery, power switch and antenna connector into a suitable enclosure will make it more robust for use in the shack.
Digital Mode Software
Two of the software packages available for digital mode PSK31 include DIGIPAN and FLDIGI. These can be downloaded from the sites below. There are others.