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)
