Rebote en Venus !!!!!!!

Hola,

Al parecer, se ha conseguido por primera vez transmitir y recibir rebotando en Venus !!!

Lo han hecho unos colegas alemanes desde el radio observatorio de Bochum.

Mas informacion en;

http://www.southgatearc.org/news/march2009/eve.htm

http://www.amsat-dl.org/index.php?option=com_content&task=view&id=166&Itemid=97

Escribió:

> Hi James, Rik, Alberto and the group,
>
> Yes an impressive distance.. even though the ERP was a bit above the usual value for amateur radio on 13 cm. AMSAT-DL has applied for, and been granted, a special permission for this experiment which expires at the end of this year.
> The *principle* was simple:
> - send a 5 minute carrier on 2.45x GHz, then
> - receive for 5 minutes, remove impulse noise (WLAN), run the signal through an FFT with ~11 Hz equivalent receiver bandwidth
> - add all received power spectra to calculate an average (*)
> - repeat the above until the sigma (standard deviation) in the frequency bins gets low enough to see the weak reflection in one of those bins.
> - while transmitting, keep the frequency constant to one or two Hz (not as easy as it sounds)
> - while receiving, permanently compensate the Doppler shift (which a marvellous piece of software by G3RUH did)
> - during the experiment, keep the dish pointed to Venus with an accuracy better than 0.1° (which another piece of software by G3RUH did)
> - hope that the 5-kW magnetron, and the cooling system (including a vaccum cleaner and a water cooler from a VW Polo) holds..
>
> (*) A single FFT is not sufficient to lift the signal out of the noise. It was between 8 and 11 dB below the noise in a 10 Hz bandwidth; the ratio of to was between 0.3 and 0.4 dB; the latter measured today when it wasn't raining. This was sufficient to "see" the signal after 2 minutes, so we didn't have to average over consecutive 5-minute-receive intervals.
>
> Each dot of the "HI"-message lasted 5 minutes, because that's the approximate travelling time... in other words, "QRSS300" dictated by Venus
>
> Details, including the "Magnetron taming" circuit by DJ4ZC will appear in English language on www.amsat-dl.org hopefully soon. This vital part of the system includes 3 PLL circuits, a servo motor controller for the coarse frequency control (slow mechanical tuning, 6 MHz, on the output waveguide), and a fast controlling loop with about 1.5 MHz (iirc) loop bandwidth which involves 2 * 4CX1000 for the 'faster' frequency control, which also provides the SSB modulation. In fact, the energy not "used" for the SSB signal at a given instance is 'moved away' (spread out) by 15 kHz to both sides of the center frequency. Maybe some of these principles can be used in class-D amplifiers for other frequencies, which finally takes us back to LF / MF-related topics <img src="smileys/teeth.gif" width="" height="" alt="" title="" class="bbcode_smiley" /> .
>
>
> Cheers,
> Wolf DL4YHF

73, Maximo - EA1DDO