On Saturday 15 December ZL6QH transmitted a low speed frequency shift keyed test signal in the 136 kHz band, as a beacon transmission for all hours of local darkness. John VE1ZJ managed to receive and positively identify signals from ZL6QH.

The path length from ZL6QH near Wellington to VE1ZJ in Sydney, Nova Scotia has been calculated as being 15,645 km. VE1ZJ received the LF signal using a 10 metre vertical with top loading, high impedance pre-amplifier, low pass filter and a TS-850 receiver. The demodulated audio was fed to a computer sound card for filtering and display of the signal using Argo software.

Weak signals were first received by VE1ZJ at 0845 UTC, which was some 40 minutes after ZL sunset at 0806 UTC and some three hours before VE1 sunrise at 1150 UTC. Best reception was from 1045 to 1138 UTC.

Previous best DX for ZL6QH was confirmed reception by Dexter W4DEX two weeks earlier, over a distance of 13,633 km. W4DEX received ZL6QH again but generally not as well as the previous time.

In June and September ZL6QH was received by VE7SL, when the test frequency was 184.4 kHz, but since then the ZL6QH signal has not been received at all, despite operators being ready to try for an LF/HF cross-band contact if propagation was satisfactory at the time.

The ZL6QH transmitted signal used frequency shift keying, with 0.4 Hz frequency shift. The uniquely coded transmission consisted of repetitive sending of QQQQQ... sent as 137.7900, 137.7900, 137.7896, 137.7900 and then a gap, with all elements being of 120 seconds (2 minutes) duration. This means sending a single Q takes ten minutes.

The ZL6QH LF signal was generated using a modified TS-850SAT, in SSB mode, fed with audio from a lap top PC, using soundcard software developed by Steve VK2ZTO. TS-850 frequency control was by means of a high performance TCXO master oscillator. The low level LF signal from the TS-850 transverter port was fed to an external LF power amplifier, and the output power was around 500 watts. The radiated power is estimated to be 4 watts.

The antenna was a long wire at the Quartz Hill club station, which is run by the Wellington Amateur Radio Club.

The ZL6QH operator was Mike ZL4OL. The next test from ZL6QH in the 136 kHz band will likely be in mid January.

Bob Vernall ZL2CAOrganiser of the ZL LF DX tests

Posted by ZL1AXG on December 15, 2001