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From: yjj@ctr.columbia.edu (Yuan Jiang)
Subject: Re: Sensitive Receivers (IR et al)
Message-ID: <1991Apr6.203416.14689@ctr.columbia.edu>
Keywords: IR,reciever,digital
Organization: Columbia University Center for Telecommunications Research
References: <1991Apr3.211135.21492@syssoft.com>
Date: Sat, 6 Apr 91 20:34:16 GMT

In article <1991Apr3.211135.21492@syssoft.com> tom@syssoft.com (Rodentia) writes:
>Greetings:
>
>    At this time, I am sending a 25KHz 25% duty cycle square wave
>(at least that's how it looks on the transmitter).  On the reciever, 
>it is very smoothed out, and resembles a sine wave of 50KHz.  I 
>suppose this is due to the harmonics present in the assymetrical
>waveform.
>
Remeber sine wave has negative cycles.  [sin(wt)]**2 is a
2w sine wave plus dc.

>    My second goal is to get the bloody 60Hz and 120Hz out of there.
>This is complicated by the fact that these sources of interference

Will a filter help?


>   PhT - PhotoTransister (IR sensitive)

They are known for being noisy and having low responsivity.
A PIN photodiode costs several dollars.

Good luck