17 Nov 2011

A local 478THz (red light) beacon !

Map showing coverage of the 471 THz optical beacon GB3CAM
Guess what - I've just discovered that not only is there a decent level of optical comms activity in my area, but there is also an active 478THz beacon beaming (almost) in my direction from the Wyton site near Huntingdon, location of the GB3CAM beacons on 10GHz and 24GHz. The beacon is a narrow beamwidth (5 degrees wide) signal which is FSK keyed between 1 and 15kHz allowing both baseband and hetrodyne optical receivers to be used. The beacon was designed by Bernie G4HJW. The distance from the beacon to my local /P high spots in the beam would be around 30km, so this will be an ideal test for the optics and receiver, when built.

6 comments:

Anonymous said...

Hello Roger

Some of the Tower blocks in the centre of Town
are changing over to energy efficient blue LEDs.
I can see these lights at a greater distance than
the red lights used on top of buildings.
Would you get a greater range with Blue LEDs or are RED
LED's better. What is the typical wavelength response
for a Photo Transistor.Can you see the red light beacon from your house. If someone was to fit an optical repeater on top of a tower with beams covering a larger footprint
that would open up a communication link to a greater number of Nanowavers.

Tony

Anonymous said...

Will you be able to do the test from the comfort
of your car or will have to do a bit of walking up to the
Local high spot to be In the beam footprint.

Tony

Roger said...

To see the Wyton beacon I will have to go out /P.

Anonymous said...

Roger

Have you designed any circuitry for this project yet?

Tony

Roger said...

So far I have used the circuit ideas from the RadCom articles back in March-May 2011. The optical head of the RX is working as expected using a reversed bias red LED as the detector.

Anonymous said...

@Anonymouns - blue light is more subjct to atmospheric scattering than red light, so you'll get better range (for a given power) at red than blue. Incidentally, that's one reason why brake lights and traffic light stop lights are red - you can see them from further away in adverse conditions.