[Laser] RE : Optics 1 : Electronics 0, tale of a partial failure

[Garnier Yves]

Paolo
A classical RX K3PGP is at least 10 dB more sensitive
than OPT201.
You can find a very sensitive RX to :
http://sd-1.archive-host.com/membres/images/22679775843705539/ChargeIntegrationphotondetector3.jpg

This RX can be put into an eyepiece with the
photodiode used as haiming reticule.
73 Yves F1AVY
http://f1avyopto.wifeo.com

--- Paolo Cravero <pcravero at as2594.net> a écrit :

> Hello.
> Here follows the report of a partial failure of an
> optical one-way contact 
> over a distance of about 9 km (5.5 mi).
> 
> TX location: my parent's flat in the suburbs of
> Torino, NW Italy.
> RX location: parking lot of Superga hill, 9km East
> of TX
> 
> In between us, right downhill the river Po and then
> 8 km of city with its 
> heating fumes, car pollution, humid air that created
> the usual urban haze. 
> Lights up to 10km were visible and the moon was
> shining on far away mountains.
> 
> TX equipment: 10mm hi-bri red led MCW driven at an
> average of 80mA
> RX equipment: OPT201 followed by 488Hz bandpass
> mounted on a 90mm telescope
> 
> On the RX side we also had an EEE netbook running
> Argo for QRSS work.
> 
> Aligning the RX was tricky. Street lights helped to
> identify the area but not 
> the actual spot. I used a pair of binoculars and
> cellphone with earphone to 
> talk to the TX site (no HAM there!). No high power
> lamps on TX side. Then an 
> idea: TX site is right under the landing path to our
> airport, and an airplane 
> was approaching. When it was right on top of the
> building we got a "now!" signal.
> 
> After was just a matter of aiming the telescope and
> search for the blinking 
> LED. It was sending 6 dashes, pause, cycle in slow
> MCW morse. Car stop lights 
> traveling around were catching out attention all
> over.
> 
> Simone, the optics owner and expert, could spot the
> TX in a couple of minutes. 
> Hooray! In the telescope the 10mm LED was clearly
> visible but as an average 
> star would look at the naked eye! Buried in yellow
> street lights and reflections.
> 
> We mounted the receiver, adjusted beaming, ..., but
> nothing. Not even the 50 
> Hz hum was audible. We replaced earphones with the
> computer DSP software but 
> nothing. Sometimes 50 Hz & friends were visible in
> the normal scroll speed, 
> but no 488 Hz line.
> 
> Now I've got to work on improvements. I need a
> larger and/or more powerful 
> source. Those 50dB over background noise we had over
> the 200m path were not 
> enough for this DX. I will add more LEDs, and maybe
> put them in the focus of a 
> beam expander (Fresnel lens or parabolic mirror).
> I will build an aiming system for the TX, even if it
> has a rather broad beam.
> 
> I will build a k3pgp receiver. I have 5x BPW34
> detectors. I'll probably follow 
> Yves's circuit. Any idea for a 2N2482 replacement?
> 
> We will wait for a windy day to repeat the
> experiment.
> 
> I will post this text with pictures on my blog in a
> few hours: 
> http://ik1zyw.blogspot.com .
> 
> 73,
> Paolo IK1ZYW
> 
> -- 
> GQRP #12058  + www.paolocravero.tk +  I QRP #476
> *   Build your external keypad for FT-817(ND)  *
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