Mike Dennison, G3XDV

LF Amateur Radio
73kHz Expeditions March/April 2003

The weekend of Friday 28 March to Tuesday 1 April 2003 saw three expeditions equipped for the 73kHz band, including the first ever operation on this band from Scotland, and one to the far south-west of England. The weekend started with Dave, GM3YXM, operating from his usual temporary location in IO75WC, some 450km from me. He made the first G-GM contact on 73kHz with G3AQC, then worked me for my 5th country on this UK-only band. Then another Dave, G0MRF, operated from the farm of fellow microwave enthusiast Simon, GM4PLM, in Ochiltree, Ayrshire. This was IO75TK, 489km from me. The site was the home of Simon GM4PLM, an area approx 750m x 750m together with a 24m high tower at one end of the property. The local ground was, however, rocky and poor for LF. They ran 350W on 73kHz. Using the callsign GM0MRF, they made the first 73kHz GM-GM QSO (with GM3YXM). Later they made other contacts, including a record-breaking two-way with G3GRO (see below) at 612km, but failed to receive me! G3GRO was in Porthcorno, Cornwall (IO70EB), some 425km from me. The station was manned by Derek, G3GRO, and Jim, M0BMU (I had a chance to join this expedition, but had to decline as it clashed with work - grrrr!). They operated from the historic Cable & Wireless Museum, but their receive capablity was badly hampered by local noise. I called many times but could not reach them. Towards the end of their operating period, they installed a loop antenna at a distance from the site and this improved reception, but I had gone QRT by then. In addition to these expeditions, there was activity from me in Hertfordshire, G3AQC and G3LDO in Sussex, G3YXM (having returned home) in Birmingham, MI0AYZ in Lisburn, and a newcomer to transmitting on 73kHz, G3WKL, in Buckinghamshire. Thus, a total of nine stations were active on 73kHz over this period, which is quite a high number. Although some activity took place using normal CW, most contacts used extremely slow Morse (QRSS). The following are screen grabs of these QRSS transmissions, using the Argo software. Only small parts of the signals are used so that the image file sizes are kept low. There is, however, enough to see the signal/noise ratio. "GM3". Part of the callsign of GM3YXM. We had a two-way QSO on Friday 28 March for the second ever G-GM on 73kHz. "GM0". Part of the callsign of GM0MRF. Their signal was visible all of the time, and occasionally audible. However, their local noise level meant they could not read my signal, though they did report seeing a trace of it. "G3Y". Part of the callsign of G3YXM. Dave had returned home to Birmingham and had fun chasing the other expeditions. He was audible at about 559 (the strong signal is what gives rise to the 'dog-bone' shape of the keying spectrum). "AQC". Part of the callsign of Laurie, G3AQC, in Sussex. He is using DFCW (more about this here) which uses different frequencies, rather than different lengths, for dots and dashes. You can read the callsign by saying "dit" for the lower 'dashes' and "dah" for the upper ones. Laurie was calling G3GRO (see below). "G3GR" (top) and "0MRF K" (bottom). Parts of the transmissions of GM0MRF (see above) and G3GRO in Cornwall "0AY" (top) and "KL O" (bottom). The very weak signal right at the top is Ian, MI0AYZ, who is some 450km from me. This was the best signal seen from him. He was also receiving me some of the time, even occasionally audibly. At the bottom is G3WKL, who is only a few tens of km from me but has only recently started to transmit on 73kHz. I was pleased to have a two-way QSO wth him. The pictures on this page mostly show the clearest reception. The 73kHz band is notoriously difficult to operate on, and one of the reasons is the high level of electrical noise. This picture clearly shows the range of noise experienced when receiving G3GRO. Fortunately in this case the really bad noise did not last long. "GM0". A really good signal late in the day from GM0MRF.

Last updated 13 April 2003