Radio Weekends: HF digital modes
This Saturday, Josh VA7ACQ, Dom VA7CRO and myself stationed ourselves at various places around the CRD with the intention of running a few tests with various digital modes on HF. Dom went up to Sidney and Josh set up at Beaver Lake, while I headed for the usual spot down at Esquimalt Lagoon.
We settled on using 20m, hoping for a balance of less QRM and greater efficiency with the compact vertical antennas that Dom and I were using, while being not as useful for ground-wave as 40m may have been. After a bit of tweaking of audio levels and picking a dial frequency of 14.088MHz, Dom and I made contact with PSK31.
Once we’d played with PSK31 for a while, we then moved to a much older mode by the name of Hellschreiber. Developed in the late 1920s, Hellschreiber (or Feldhellschreiber) sends text as a series of pixels, scanned left to right.
After this, we tried a whole bunch of other modes, including RTTY, MT63, Olivia, and MFSK – where Josh and I even managed to exchange small images! It was also a useful test of the RSID functionality in both FLdigi (which I was using) and DM780 (which both Josh and Dom were using), which sends a brief burst of MFSK before the actual transmission to both identify the mode being used and to centre the decoder on the right frequency.
Some findings from the afternoon’s experiments were that MT63 can be very particular about being on the correct frequency, that DM780 uses fixed centre frequencies for MT63 whereas FLdigi doesn’t, and – very much related to the first two – that the USB sound card I use for digital modes produces audio that is off by a not insignificant amount – about 40Hz.
By now it was starting to get a bit on the cold side, so we all made our way to Six Mile to warm up and for a much-needed beer.