Re: ATM here's another pulsar idea...

[Bob Bond <rgb@ncube.com>]

After spending last winter with mechanical shutters, I thought of listening 
to the pulsars and tried this too, earlier this year.  The problem is the 
same as it is for the mechanical shutter: the star is too dim.

I took a 3 month tour through photodiode land, built up a system with low 
noise op amps, Hamamatsu photodiodes, 100 Meg ohm resistors, the whole nine 
yards.   With this system in my 16inch I can detect down to maybe 8th mag 
stars.  I currently just run the signal into a milivolt meter and so have 
no integration time.

With a more sophisticated circuit such as the one Optec uses on the SSP-3 
(see http://www.optecinc.com/astronomy/products/ssp-3.html  ) and 
sufficient integration time, on the order of seconds, I expect I could do 
better and actually sense the star. I use the same photodiode Optec does. 
There is no way I will be able to see a 30HZ signal.  If you check the 
referenced web page, Optec says you'll need 100 seconds of integration for 
a 15th mag star with an 11 inch scope.

The fix is more aperture, same as for the mechanical shutter.

                         Bob

At 10:37 PM 8/28/99 +0000, P.K. Ferrick wrote:


>I once built a simple device that consisted mainly of a phototransistor
>hooked to the input of an audio amp, and had all sorts of fun
>"listening" to various light sources...incandescent lights 'swish',
>flourescent lights hum at 60 Hz, and things like multiplexed
>LED displays or computer screens hum buzz, depending on the scan rate.
>Because of the eye's persistance of vision, anything that flashes more
>often than something like 30 Hz (correct me if I'm wrong) is "smoothed
>out" and appears continuous.
>
>Which is an extremely long-winded way to say, "Has anybody tried
>_listening_ to the pulsar lately?!?!?"
>
>regards,
>patrick
>