[Laser] daytime optical contacts

[Tim Toast]

hi Stuart,
 
I joined the nanowave group as soon as i heard about it. Lots to take in at first to catch up. It seems
like a really lively place compared to all the others lately!... I somehow managed to put some sort 
of voodoo hex on the Aussie group by mentioning using stars as standard candles (for seeing how 
sensitive a receiver is) - no one has posted since April ! - It's really just the cold weather 
down there this time of year, most likely, and come summer they'll break out the gear and start 
stirring again.
 
This business with the single optics got me thinking of trying laser diodes as transceivers just to see
for myself if or how well they work. And about some way to use single optics with Independent 
devices just for the convenience  / advantage of it.
 
You guys in the UK may have an advantage over some by being all in a big bunch - in a 600 x 300 
mile or so area. More than half of you are probably within 300 miles of each other at most. You 
should really try some NLOS weather permitting. Using some high power LED arrays or other high 
output format like xenon strobes. I have at least one other optical experimenter within about 300 
miles of me that i've mentioned an NLOS attempt with. It wouldn't take very many people to make 
a network that could span a continent if NLOS is possible at those ranges. 
 
About the multiplexing, now it seems kind of silly of me pondering turning expensive external 
transceivers on and off more than ten times a second when using a transverter setup.  All in all 
a lost cause probably. It might make more sense with a stand-alone unit that generates its own 
subcarrier and could be designed to handle the abuse. I tend to agree with you though that 
full duplex is not worth the trouble.
 
I think i speak for most people in here that posts on any optical comms subject are welcome 
regardless of the name on the door :-) After all, we haven't had a good fight in like 12 months now.
LOL
 
Good luck with the 46km attempt in full daylight! 
 
-toast
 
 
>    1. daytime optical contacts (Stuart)
>    2. Re: daytime optical contacts (MICHAEL COUTURE)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Thu, 25 Aug 2011 12:35:06 -0400
> From: Stuart <stuart.wisher at talktalk.net>
> Subject: [Laser] daytime optical contacts
> To: laser at mailman.qth.net
> Message-ID: <8CE315C14CE91EB-57C-A247 at FRR2-L30./f>
> Content-Type: text/plain; charset="us-ascii"
> 
> 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
>