[Ronja] Vacuum tube in Ronja preamplifier

[Gullik Webjorn]

> 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 ?
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
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?

Gullik

CL<

>
> Regards,
>
> Gullik
>
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>
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