[Laser] A lot but very little

[Chuck Hast]

On 1/2/07, Kerry Banke <kbanke at qualcomm.com> wrote:
>
> Chuck - I'm assuming the response is being limited by the
> receiver.  I have been driving the low cost laser pointers (
> internally only a resistor and laser diode) with a good frequency
> response of at least 500 MHz and I suspect that is still limited by
> my receiver.  If you want to see what is doable from a frequency
> response standpoint  then I'd go to a 50 ohm system but then you need
> some form of modulation to pass through RFamplifiers. With the system
> you have , you will probably need to reduce the input resistance to
> improve the frequency response but of course that will reduce your
> sensitivity.  For a frequency response  test I drive an LED with a
> signal generator and look at the receiver output vs frequency ( for
> responses in the low  MHz range). For higher frequencies I use the
> laser pointer.  The K3PGP front end is great for low frequency ( 2
> KHz or lower depending on the PIN diode), weak signal work but you
> may be better off with a transimpedance amp design for higher speed data.
>   - Kerry N6IZW -
>
> At 06:18 PM 12/26/2006, you wrote:
> >Folks,
> >I know that most of the thrust of the list is to low signal level
> >long distance
> >work, but I am working in the high speed high signal level area, I have
> >been looking, I find a lot of info about low speed low signal level systems
> >but so far not too much luck with the high speed links that I would like to
> >build. I have looked at Sam's at k3pgp, and the site down under. Along
> >with many others, but still not too much into. I wonder if any of you have
> >any other recommendations?
> >
> >I have been able to move data at up to 9k6 b/s but I can do much better
> >than that with RF.
> >
> >I have also been able to get my lasers to generate data at up to that
> >speed but when I try to go much higher it appears that something is
> >slowing things down. The test transmit end is a laser pointer, I opened
> >it up and found that it is a regulated one, I went in and used a VN10
> >to key the laser, but still can not get it to switch faster than about 9k6.
> >
> >It appears that the rise time is good, but the shut off time is ramped
> >down. But that maybe a artifact of my reciever, but again I am not
> >sure, I have tried a switched LED, and it appears to  track the led
> >while it is switched at up to 38k4.
> >
> >Any good recommendations for power users?
> >
> >--
> >Chuck Hast  -- KP4DJT --
> >To paraphrase my flight instructor;
> >"the only dumb question is the one you DID NOT ask resulting in my going
> >out and having to identify your bits and pieces in the midst of torn
> >and twisted metal."
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-- 
Chuck Hast  -- KP4DJT --
To paraphrase my flight instructor;
"the only dumb question is the one you DID NOT ask resulting in my going
out and having to identify your bits and pieces in the midst of torn
and twisted metal."