[Fwd: LF: DX reception of ZL6QH by W4DEX]

[Andre Kesteloot]

Vernall wrote:

> CLAIM OF ZL TO W4 AMATEUR LF DX
> 4 December 2001
>
> On Saturday 1 December ZL6QH sited near Wellington, New Zealand transmitted
> a low speed frequency shift keyed test signal in the 136 kHz band.  This was
> the first time that DX testing in he 136 kHz band has been tried by ZL6QH,
> since having the 135.7 - 137.8 kHz band recently added to the club station
> Low Frequency Permit.  Various DX listeners had prior knowledge of the ZL6QH
> test transmission, which ran for all hours of local darkness.
>
> Dexter W4DEX managed to receive and positively identify signals from ZL6QH.
> The path length from ZL6QH to W4DEX in North Carolina has been calculated as
> 13,633 km.  W4DEX used receiving equipment with the audio fed to a computer
> sound card for filtering and display of the signal.  This is now a popular
> technique used for "below the noise" detection of amateur LF signals, as
> ZL6QH was using 120 second dot length (each transmitted bit was 2 minutes)
> and there can be nil detected by ear, yet coding of the wanted signal can be
> seen after DSP filtering and displaying on the screen.  The screen display
> can be captured and saved as a file, as a record of what was received, and
> for passing to others by electronic means.
>
> Best reception was reported as being between about 0904 and 0950 UTC, which
> is approximately one to two hours after ZL6QH sunset at 0800 UTC and about
> two to three hours before W4DEX sunrise at 1212 UTC.
>
> The radio equipment used by W4DEX was a square loop antenna, 2.3 metres per
> side, balanced pre-amplifier feeding an HP3586B selective level meter.
>
> The ZL6QH transmitted signal used dual frequency 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 timing was such that the
> start of a fresh Q was on the hour, so coding by absolute timing was another
> factor that could be used for analysis of weak signal detection.
>
> 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 Bob ZL2CA.
>
> The next test from ZL6QH in the 136 kHz band will be on 15 December.
>
> Bob Vernall ZL2CA
> Organiser of the ZL LF DX tests