[Laser] NO RX XE2AT

[Art]

Hi Al,

I have a more basic question....

You report both QSO partners could see each others beam.........  But, you=
=20
only comment on your receiving attempt and what you saw from your end of=20
the path.

I wonder if you can give more details please.

Both stations were able to see each others laser???

Both stations were unable to hear the others signal, or was there only one=
=20
attempt to receive?

If both stations were attempting to receive, did both stations use a 4 inch=
=20
lens???

------------------------------------

My guess would be that the Ramsey transceivers aren't quite up to the task=
=20
of distances that great. They use a carrier to send the information on, so=
=20
your receiver has to be responsive at the carrier frequency-which means you=
=20
give up a VERY LARGE degree of sensitivity due to this overhead.

The noise is proportional to the square of the relative bandwidth. Since=20
your receiver has to be sensitive to the carrier frequency (which I think=20
was 30 KHz), you have a greatly reduced ability to copy weak signals.

Comparing 2 identical systems, one receiving at 30 Khz and the other at 1=20
Khz.... The transmitter for the 30 Khz link would have to be 900 times=20
stronger to give the same quality of reception.

I think your results would be very much different if you used a shielded=20
Burr Brown opt101 receiver chip with the bandwidth set to 1 Khz by the=20
external feedback resistor. Your transmitter would be switched at (about) 1=
=20
Khz, and it's a much simpler circuit. This would send a tone only, unless=20
you modulated the laser with audio from a microphone.

------------------------------------

You did not hear any interference from the city lights because your carrier=
=20
frequency was far removed from the 50 or 60 Hz noise emitted by the city=
 light.

You probably did not overload the photodiode itself, they have incredible=20
dynamic range! It is possible that you overloaded the receiver electronics=
=20
though. I don't have a schematic for these Ramsey units. But you can=20
improve the receivers electronics rejection of  50/60 Hz overload by using=
=20
appropriately sized coupling cap. You want to insure that the receiver=20
carrier can pass from the photodiode to teh receiver without much=20
attenuation, but the 50/60 Hz must be attenuated.

Does anyone have a schematic of these units??

Art




At 09:10 AM 2/10/04, you wrote:
>Hi boys yesterday we make some test at 20 miles and after 2 hours we can=20
>saw the both sides of lasers !! was a great experience but NO reception=20
>!!!! I can see a lot of city lights but no noise beaming the receiver to=20
>lights, I am using a 4 inches lens and the Ramsey Electronic Kit.
>The Laser was very strong but I think is the LED on the receiver, What I=20
>can do ?
>73 de Al
>XE2AT
>
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