PSK31 – for exciting HF band QRP
This is a demonstration of typical QRP QSO using 5W (perhaps it was 3-4 W) into 1/4λ vertical ground plane antennas used at both ends of the circuit. The distance was approximately 5800Km between a station with the QTH in Sweden and my QTH in New Delhi, India. The QSO was conducted on the 17m band at a little after 14:30 UTC. The PSK31 signal was not visible on the band-scope of my transceiver but was barely visible as occasional yellow speckles on the waterfall display of FLdigi decoder software that I used.
Moreover, we decided to make the environment more hostile by operating on a frequency that was adjacent to that of another transmission from Pretoria, South Africa. Its signal strength into New Delhi was a wee bit stronger (could be +3-6 dB) than the PSK31 signal coming from Sweden on my vertical antenna. However, it was not strong enough to even noticeably deflect the S-meter needle on my TXR. With the correct choice of band (just below MUF) which resulted in minimum ionospheric signal phase shift (distortion), we successfully established a weak signal and zero error transmission circuit. You might note that there is not a single garbled character in the reception. Of course, the proper setup of PSK31 modulation played a very vital part in achieving this.
Above is a video compilation of an experimental round of the QSO as witnessed at my end in India. This video includes a partial overlay to show how the signal appeared on my TXR waterfall and S-meter while the PSK31 was being decoded. In the beginning, I have also included a propagation map that was created with 3W TX power, PSK31 mode, and 1/4λ Vertical on both ends. The cross-hair on the map indicates the DX location while the red-colored dot in south Africa marks Pretoria. My QTH is self-explanatory.
Those who might be interested may watch the video carefully. You may also pause it at any time, especially during the initial propagation map to familiarize with various prevailing propagation parameters which existed at that time.
I hope you find the experiment interesting and might want to work PSK31 with actual low signals and controlled modulation depths after watching the video and thus leverage the real fun which this robust digital mode can offer.