[Laser] discrete vs op amp sensitivity

[Art]

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>Are you talking about the  Australian Optical_DX Yahoogroups ?
>Yves F1AVY

Yves, the group I was talking about was the softrock_40 yahoo group. 
These are rf types using and experimenting with Tayloe (QSD) 
detectors, which use synchronized analog switches to convert the RF 
signal directly to baseband rather than using a superhet type 
mixer-the advantage is a detector with a 1 db noise figure rather 
than a 7 db noise figure which you get from a conventional mixer.

They are an offshoot of the more popular SDR-1000 transceiver, which 
is an all band commercial product based on the QSD detector.

After the audio is recovered, it is sent to a sound card where the I 
and Q phases are combined in software to give image 
cancellation-which is atypical in conventional direct conversion receivers.

Anyway, the group doesn't have any interest in laser communications, 
but they have been discussing noise relative to source impedance in 
op amps AND which sound card allows them to copy a weaker signal 
(with all other factors held constant).

Obviously, more sound card bits improves the dynamic range, thus the 
ability to copy a weaker signal is enhanced.

Both of these topics are discussed there and I've been a member for a 
long time. I suspect the 'noise' problem in a laser receiver is very 
similar to the 'noise' problem in an rf receiver, so much of their 
discussion is highly pertinent to our laser group as well.

Regards,

Art