[Laser] Simple optical beacon experiment in San Diego

[KY1K]

Hi Kerry,

I've become interested in SDR recently, and have been using spectrum 
lab quite a bit.

I found that sometimes the front end saturates, and sometimes the 
ability to sample the front end in a linear mode fails-effectively 
meaning the sound card doesn't have enough dynamic range to display 
the entire output spectrum properly.

These are 2 separate and distinct issues, each has it's own remedy.

I'm curious whether your receiver is outputting dc to Vcc, meaning 
the receiver itself is saturating.....

Or, does spectrum labs 'input' monitor turn red, effectively meaning 
the sound card is being over driven???

Or both??!!

Just curious.

If you use a fairly wideband optical bandpass filter on the receiver 
input, BOTH types of over load will improve. But, ultimately, you 
need to make sure the receiver isn't saturated before addressing the 
possibility that the sound card is running out of gas (not enough 
dynamic range to sample the entire spectrum).

Regards,

Art


At 12:39 PM 3/13/2006, you wrote:
>We have installed a simple LED optical beacon on San Miguel Mt. in 
>San Diego. The beacon is a Luxeon 1W red LED with 15 Degree (30 deg 
>total)  integrated lens.  It is powered by a square wave at about 
>700 Hz and has an identification of N6IZW once each minute.  At 8 
>miles the beacon was  visible through a 7X20 mm  rifle scope mounted 
>on my K3PGP type receiver with 4" glass lens.  The tone was barely 
>detectable by ear as there are several lights on the same mountain 
>generating huge quantities of 60 Hz and harmonics.  Using Spectrum 
>Lab SW on my laptop,  the tone was readily observed and disappeared 
>during the identification period.  The tone strength was only 
>slightly stronger than the 720 Hz harmonics ( 12th harmonic of 60 Hz 
>probably due to receiver overload) of the other lights on the hill. 
>The frequency response of the receiver  currently extends down to a 
>few tens of Hertz so is very much affected by 60/120Hz lights. 
>Adding a good high pass filter to the front end should make the 
>beacon much easier to copy. Thanks  goes to Greg, K6QPV for putting 
>the beacon up on the hill and setting it up with a control link to 
>turn it on & off.
>  - Kerry Banke N6IZW -