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Date: Fri, 27 Mar 2009 20:33:32 +0100
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Subject: Re: LF: Re: Lazy Man's CW made it to Venus and back
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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 <signal plus noise> to <noise> 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 <g> .


Cheers,
  Wolf DL4YHF .

James Moritz schrieb:
> Dear Wolf, LF Group,
>
> Congratulations on an excellent achievement - I expect it has broken a 
> few DX records! I will be interested to hear more about how it was 
> done, when information becomes available.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>
>