[Laser] daytime optical contacts

[Stuart]

Hello Tim,


Sorry it has been a while again since I last "chipped in". I have been busy on the "UKnanowaves" Yahoo group which I see you have joined as well.


Ok on all your comments, The wavelength mismatch doe not seem to be a problem for the LEDs I am using. They are at least 30nm wide bandwidth, that is probably why. The effect will probably be much narrower with lasers, but I know it has been made to work in the past.


The big gain as you recognise with my LED transceiver is the use of a single optical system for both receive and transmit. I do not feel the need for duplex, as what we have just works like normal simplex amateur radio, so no need for a multiplex system. There is a small delay when you go back to receive as it takes a few ms to charge the LED up to 43V reverse bias anyway, with big capacitors on the decoupling you can see and hear the signal coming up as the optimum voltage is approached.. Plus on simplex, there is a nice opportunity to optimise the alignment on receive as your QSO partner talks, in the knowledge that you will also put a better signal out on transmit when your turn comes.


We are just about to try a contact over a 46km path close to local noon, and in addition we are going to try not to use any visible beacon or strobe to line up to start with, although we will use the optical beacons if that does not work out. We will be treating the contact rather like a rather narrow beamwidth microwave contact (current beamwidth of our system is 0.3 degrees in total). I am also going to trial an iris plate attenuator provided we make contact, I can drop both RX and TX signals by 6dB or 12dB by reducing the aperture. I am hoping this will give us a guide re further range possibilities. I will let you know how we get on.


Stuart, G8CYW