[Ronja] Channel Capacity

Karel Kulhavy clock at twibright.com
Mon Oct 22 15:42:48 BST 2007


On Mon, Oct 22, 2007 at 11:47:04AM +0200, Gullik Webjorn wrote:
> Clock,
> 
> How do we design optical heterodyne Ronja?

Optical heterodyne is done by mixing the optical input signal with a local
source that is coherent to it directly on the photodiode. You just shine the
received signal and local oscillator both on the diode. The difference between
the spectral line frequencies should appear on the photodiode output.

<lol>or you put the optical fiber into your sound card, record with sampling
frequency of 1000,000 GHz and then open in Audacity and look at the
spectrum</lol>

CL<
> 
> Then we might actually go somewhere towards the 77,000 Ghz :-)
> 
> Gullik
> 
> -----Ursprungligt meddelande-----
> Fran: ronja-bounces+gullik.webjorn=flysta.net at lists.pointless.net
> [mailto:ronja-bounces+gullik.webjorn=flysta.net at lists.pointless.net]For
> Karel Kulhavy
> Skickat: den 22 oktober 2007 11:05
> Till: Twibright Ronja
> Amne: Re: [Ronja] Channel Capacity
> 
> 
> On Sun, Oct 21, 2007 at 05:24:00PM +0200, Jakub Ladman wrote:
> > Dne Friday 19 October 2007 19:32:37 Karel Kulhavy napsal(a):
> > > On Fri, Oct 19, 2007 at 10:38:56AM +0200, Daniel Polak wrote:
> > > > Whats the theoretical channel capacity from Ronja Tetrapolis
> calculated
> > > > with the shannon-hartley theorem? I tried to calculate it but I'm not
> > > > sure about the bandwidth. What's the bandwidth in hertz?
> > >
> > > I don't know. What I know for sure it's constantly changing with clouds
> > > passing over the landscape, fog, day/night etc. The bandwidth is about
> > > 100nm which is 77,000 GHz.
> >
> > Bandwidth of ronja circuits 77GHz? This is absolute nonsense.
> > I have not calculated it, but i estimate it about 50MHz
> 
> The transmission bandwidth is like this due to spectral width of the LED
> diode.
> It's an electromagnetic signal at 480,000 GHz, 77,000 GHz wide ;-) Then it
> is
> demodulated like envelope detected on the photodiode. The electronics
> bandwidth
> is aimed at 16MHz.
> 
> But I don't know if Shannon theorem takes quantum effects into the account.
> On
> this frequency they are already strong.
> 
> CL<
> 
> >
> > Jakub Ladman
> >
> > >
> > > CL<
> > >
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