Re: VLF: DK7FC 8270.005 and DF6NM 8270.005139 at DL0AO grabber

[Markus Vester <markusvester@aol.com>]

The combined signal at DL0AO has been growing steadily during the last hour, now at 21 UT we must be close to the maximum. For anyone who'd like to watch it live, we'd like to announce an online VLF grabber in Amberg:

 http://df6nm.bplaced.net/dl0ao/VLFgrabber/vlfgrabber_dl0ao.htm

The receive antenna is still an improvised long wire near a fence, but it seems to work quite well already. Tom and Bernd are building an active E.probe which will be installed soon.

Best 73,
Markus



-----Ursprüngliche Mitteilung-----
Von: Markus Vester <markusvester@aol.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Fr, 28. Apr 2017 22:11
Betreff: VLF: DK7FC 8270.005 and DF6NM 8270.005139

Around 17 UT, DK7FC has started another carrier on 8270.005 Hz. Since 20 UT, I am joining in on a slightly higher frequency, 8270.005 + 1/7200 Hz (i.e. 138.89 uHz up). Compared to Stefan, I can achieve about 60% current into 60% effective antenna height, so my ERP should be ~ 9 dB weaker.

The two carriers will be resolved by a 47 uHz spectrogram. But at lower resolution (e.g. 424 uHz), they will merge into a two-hour sinusoidal beat pattern. The idea is to use that to indirectly measure our phase difference, by observing the times of maxima and minima at DL0AO in Amberg (and perhaps also in Paul's spectrogram). As both carriers are GPS locked, the two transmitters (or rather the two near-field pickup probe signals which are compared to GPS) will be in phase at even hours (UT), and in antiphase at odd hours. Using the known path difference (178 km = 4.9 lambda) to DL0AO, we could in principle calibrate the phase difference of our differently built phase-feedback probes. This could then be used in the future to obtain 2 to 3 dB directional gain in any desired direction.

One shortcoming of the measurement may be that while the 48 km path from myself to DL0AO is groundwave dominated, there will be a strong and variable skywave contribution from DK7FC at 226 km. So any array steering calculated therefrom may be incorrect during the daytime, or for long-distance paths with skywave from both sources. It might however be possible to account for the diurnal phase change using the DK7FC-DF6NM colour-phase measurement from Jan 28/29.

All the best,
Markus (DF6NM)