[Ronja] Vacuum tube in Ronja preamplifier

Karel Kulhavy clock at twibright.com
Mon Oct 15 10:57:05 BST 2007

On Mon, Oct 15, 2007 at 10:47:37AM +0200, Gullik Webjorn wrote:
> >Sun dominates during day. Receiver noise dominates during night or low
> light
> >conditions.
> Then daytime performance is the limit, isn?t it? If the light could be

There isn't any limit. If you increase the sensitivity then the downtime goes
down. You have fogs during night.

> filtered,

OK find an optical filter which is cheap easy to get available around the whole
world and actually brings more benefit by filtering the noise than the
disadvantage it brings for the signal with insertion loss.

> maybee we could get rid of excess sun energy, and get receiver to be
> limiting factor.
> >No I didn't measure input sensitivity. In what units is it supposed to be
> >measured?
> The convention seems to be dBm @ SNR, or dBm @ BER, I have always tried to
> work
> in these measurements, because then it is possible to compare what I can do
> in the lab
> with what other people / products achieve.
> I usually do SNR "estimates", you can do that by looking at a scope, and
> just compare
> no-signal to signal conditions visually, it does not work so good for SNR <
> 8, because
> it is hard to evaluate "noise" vs. scope tracewidth.
> I guess for Ronja the RSSI could be calibrated.
> I have used a "large" photo diode ( small solar cell ). With that, a
> resistor and a multimeter,
> good optical power measurements can be made. It has to be calibrated for
> wavelength, but after
> that it is perfectly good. Even better, a Hamamatsu S1337-66BR is a 5.6 x
> 5.6 mm photodiode ( $50 )
> that can be used to measure light sources by masuring short circuit current.
> Then the datasheet
> can be used to calibrate against wavelength conversion efficiency ( A/W)
> For the Ronja RX, I think a measure of sensitivity would be good for people
> troubleshooting,
> or trying to optimise performance / distance.
> One experiment you have done which tells a lot, but maybee could be improved
> is the "floor test".
> It should be possible to estimate the power that reaches the RX without
> optics. It should also be
> possible to take the test transmitter (starquake) and test it with a
> commercial powermeter at a certain
> distance.
> Just some thoughts...
> Gullik
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