[Laser] Simple optical beacon experiment in San Diego

[Kerry Banke]

Art - I watch to make sure that the sound card is not being over driven . 
The issue I have is with the audio preamp stages being driven to near 
saturation with the large background signals from other light 
sources.  Again, most of this is probably due to the very low  end audio 
frequency response of the setup I'm presently running.
  - Kery N6IZW -

At 10:39 AM 3/13/2006, you wrote:
>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 -
>
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