Markus and Stefan, That was a fascinating experiment, thanks for providing link to grabber with the combined signal. It is as you stated fascinating to visualize your multi-lobe antenna pattern slowly sweeping over Europe! I looked at the spectrogram for any signs of phase sensitivity to time-varying polarization ellipticity from non-vertical antenna at 226 km and of course saw only the well-behaved signature that you described. Ratiometric AoA-measurement variations are well documented for such conditions at VLF but I think that those may not manifest in significant phase variations unless the receiver antenna is placed near angulated or curved conductive items. Nice coherent signal reinforcement… and nulling, and phase-offset measurement. An excellent experiment. 73, Jim AA5BW From: [email protected] [mailto:[email protected]] On Behalf Of Markus Vester
Sent: Friday, April 28, 2017 8:19 PM
To: [email protected]
Subject: Re: VLF: DK7FC 8270.005 and DF6NM 8270.005139 at DL0AO grabber Stefan's carrier went off air at 23:07, and I left mine on for another hour until 00:03 UT.
On the DL0AO grabber, a sharp minimum occured just before the 21:43 UT screenshot. Considering the FFT half length (20 min), antiphase happened at 21:22 (+- 2) minutes, implying that the signals were in-phase 22 minutes after the even hour. This means that my signal phase at DL0AO is -66° (i.e. retarded) versus DK7FC. From the 4.9 lambda path difference we would expect +1764° = -36°. Thus my TX signal is 30° later and my local pickup probe 30° faster than Stefan's.
Stefan's trace was well visible in Todmorden and also on the G3ZJO grabber. There was a bit of QSB on both, but I'm not quite sure whether that is really due to the contribution from here.
73 and good night,
Markus
-----Ursprüngliche Mitteilung-----
Von: Markus Vester <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Fr, 28. Apr 2017 23:52
Betreff: Re: VLF: DK7FC 8270.005 and DF6NM 8270.005139 at DL0AO grabber
Hi Stefan,
fascinating, energy from nothing ;-) The trick is of course that the voltages are added rather than power: 1 + 0.355 = 1.355 = +2.6 dB.
Now at 21:43 we are apparently approaching the minimum at DL0AO. It's fascinating to visualize our multi-lobe antenna pattern, slowly sweeping over Europe. Hope it won't rain so we can continue for a couple of hours more.
Best regards,
Markus
-----Ursprüngliche Mitteilung-----
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Fr, 28. Apr 2017 23:33
Betreff: Re: VLF: DK7FC 8270.005 and DF6NM 8270.005139 at DL0AO grabber Hi Markus,
A nice experiment! I'm curious about Pauls results.
But how can our combined signal be 2...3 dB stronger when your signal is 9 dB weaker?
BTW i can see you on my grabber in 424 uHz although i am transmitting in just 2.5 mHz 'distance' with a 40 dB stronger signal level :-)
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
73, Stefan
Am 28.04.2017 23:10, schrieb Markus Vester: 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 <[email protected]>
An: rsgb_lf_group <[email protected]>
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)
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