[Ronja] Vacuum tube in Ronja preamplifier

Karel Kulhavy clock at twibright.com
Mon Oct 15 08:00:26 BST 2007


On Mon, Oct 15, 2007 at 01:07:51AM +0200, Gullik Webjorn wrote:
> > Rec power = 0.017 W * 0.0132/(2.66)^2 = 31 uW = -45 dBW = -15 dBm
> 
> 
> >No the spot calculation assumes that the radiated pattern is a sharp
> uniform
> >circle which is not true.
> 
> Indeed, but with your "focusing magic" we are essentially seeing the average
> LED die ( a part of that is ) with our little aperture in the middle of the
> spot...
> 
> >it also ignores 4 glass-air interfaces which reflect power 5% each.
> 
> Ok, so we correct the figure with (0.95)^4 = -0.8 dB
> 
> >It also ignores the loss of power in the glass itself which is not
> negligible
> >in these window-glass Chinese lenses.
> 
> True, but better glass lenses (still VERY cheap) exists, mine come from
> India
> and are optical glass. ( < 5 euro each) They come from school material
> supply.
> I also have beautiful PMMA 130 mm lenses, lightweight, very good presicion,
> slight cromatic abberation, but this is single wavelength (more or less)
> 
> >It also assumes that the receiver lens is able to concentrate all incoming
> >light onto the detector which is not true.
> 
> I can get remote light down onto 0.5 mm PIN diode chip, i.e. projected image
> < 0.5 mm.
> But it is better to use a larger PIN, angular precision is easier.
> 
> >Fibre optic system doesn't have ambient light from the sun with the
> associated
> >strong noise source.
> 
> Indeed, but if the *sun* dominates, then receiver noise factor is not a big
> deal ?

Sun dominates during day. Receiver noise dominates during night or low light
conditions.

> Then only fix is filtering / optical screening to lower sun optical noise,
> is that not so?
> 
> Back to the original discussion, I think the Vacuum tube idea is
> interesting, I just question
> what a lower noise factor would do to performance.
> 
> Have you looked at PMT?s, photomultipliers are a very nice optical input

Yes.

> device, however
> GREEN or BLUE light would match the photocathodes much better than red. Some
> types work
> with down to 500 V, and since the current is uA, a very simple HT supply
> will work. They can
> count single photons !!! and have conversion efficiencies at 100-1000 A/W.
> Expensive however....!
> There are "sun-blind" PMTs, where visible and IR light is not converted.
> These can be bought surplus for small pennies....
> 
> Question: what is the typical input sensitivity of a Ronja Receiver, I
> assume you have
> measured it, but I cant find it on the web site?

No I didn't measure input sensitivity. In what units is it supposed to be
measured?

CL<
> 
> Gullik
> 
> CL<
> 
> >
> > Regards,
> >
> > Gullik
> >
> >
> >
> >
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