A series of experiments carried out by LX1DU over a long period of time yielded interesting results in relation to the propagation of signals at 10 GHz.
Approximately 400 link-ups were carried out as part of a series of experiments by LX1DU in relation to the propagation of microwaves in the 10 GHz range. After every link-up, notes were made regarding the time, temperature, atmospheric humidity, air pressure, cloud cover, and, if applicable, mist, rain, and the field strengths of the responding station and of various beacons at 23 and 13 cm.
Later the data was fed into a PC and used to create diagrams. Analysis revealed that outstanding field strengths could be obtained at 10 GHz in bad weather, whilst the 23cm or 13cm beacons could be heard only very faintly, or not at all!
The results show that the 3cm band is clearly a "bad weather band". The diagram in Fig.1 clearly shows that, even with light cloud cover, an increase in field strength of up to 10 dB can be obtained, and with heavy cloud cover there is very often an increase of up to 25 dB. We should not overlook here that the two stations were almost 200 km. apart.
As the results of this long-term study can be interpreted as showing a direct link between the increase in field strength and the cloud cover, it was an obvious idea to construct a beacon which could permanently beam a signal into the clouds.
The initial cloud scatter beacon experiments were unsuccessful. As later became clear, the power was too weak. It was not until a test rig was set up with a paraboloic reflector with a diameter of 1.3 m., a gain of 40 dB, and a beacon output power of 500 mW that success was achieved. The beacon has been operating for months at 10.368040 GHz, under the call sign LX1DU. Its signals have already been heard, with good field strengths from various QRA locators.
Fig.2 makes it clear how the beacon was assembled. A remote 96 MHz crystal oscillator, with a power of app. 10 mW, powers a twelve-fold multiplier (through a thin coaxial cable) with a subsequent amplifier, which thus yields app. 1 Watt at 1,152 MHz. The subsequent nine-fold multiplier brings the signal up to 10.368 MHz. It is now amplified again, through a power amplifier, to 0.6 Watts. The signal is fed to the paraboloic reflector, by means of wave guides, type WG/16, with an overall length of 12 m., and of a series of special microwave relays. In order to obtain very good long-term stability, the crystal oscillator was sunk app. 3m deep into the ground in a closed plastic tube with a diameter of 50 mm.. At this depth, the temperature is already relatively constant at 12.5 degrees. In order to make this beacon complete, it also has a call sign transmitter for the location and transmits call signs in Morse code.
In conjunction with a computer and a two-axis rotor (resolution 0.2 degrees), a reflection measurement unit searches for a strongly reflecting cloud formation. The information on the degree of reflection is fed to the computer, which now makes a fine correction. After precise setting, the rotor is automatically stopped, and the reflection measurement unit is separated from the antenna. The beacon signal is now fed to the paraboloic antenna through a wave guide switch and beamed into the clouds. If the signal is heard on the 10368.040 MHz frequency, we know that cloud scatter is present. The antenna is aligned for maximum field strength. Now we can pick up scatter links through this cloud formation. If there are no clouds in the sky, the beacon can scarcely be heard. Very strong reflections have been measured in the direction of the Moselle valley (Az 63°, EI 3°). It seems that the cloud pattern along the Moselle valley plays a decisive role. Not all clouds have such good reflection characteristics. Thick black storm clouds are the most suitable. The range within which link-ups can be carried out depends on the height of the cloud formation.
If you have weather images from Meteosat available, ideally in time-lapse form, the cloud patterns, wind direction, speed and approximate arrival time of cloud formations can be estimated.