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Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!yjj
From: yjj@ctr.columbia.edu (Yuan Jiang)
Subject: Re: Sensitive Receivers (IR et al)
Message-ID: <1991Apr14.052133.5019@ctr.columbia.edu>
Keywords: IR,reciever,digital
Organization: Columbia University Center for Telecommunications Research
References: <1991Apr3.211135.21492@syssoft.com> <1991Apr6.203416.14689@ctr.columbia.edu> <1991Apr10.040631.15699@syssoft.com>
Date: Sun, 14 Apr 91 05:21:33 GMT

In article <1991Apr10.040631.15699@syssoft.com> tom@ssi.UUCP (Rodentia) writes:
>In article <1991Apr6.203416.14689@ctr.columbia.edu> yjj@ctr.columbia.edu (Yuan Jiang) writes:
>>In article <1991Apr3.211135.21492@syssoft.com> tom@syssoft.com (Rodentia) writes:
>>>Greetings:
>>>
>>>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.
>>
>   I understand that there is biasing involved, but the receiver is
>AC coupled.  Where does the squaring of the wave come into play?  The
>asymmetry to which I was referring was in the duty cycle.

I don't remember whether you specified what kind of light source you
used.  The squaring applies to lamps.  If you are using a LED or laser
and operating in the linear region, then I don't have any clue where
the 2w frequency is from.

>
>>>    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?
>>
>   I imagine so, any suggestions as to what stage would be the 
>filter?  Is making one of the op amps an active filter best?

Depending on where this line frequency comes in.  I guess it's from
the light source since 2w(120Hz) is there.  Filter the DC power
supply.  If possible, seal everything is a metal box.
>>