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From: tom@syssoft.com (Rodentia)
Newsgroups: sci.electronics,sci.optics
Subject: Re: Sensitive Receivers (IR et al)
Keywords: IR,reciever,digital
Message-ID: <1991Apr10.040631.15699@syssoft.com>
Date: 10 Apr 91 04:06:31 GMT
References: <1991Apr3.211135.21492@syssoft.com> <1991Apr6.203416.14689@ctr.columbia.edu>
Reply-To: tom@ssi.UUCP (Rodentia)
Organization: Systems & Software, Inc., Irvine, CA
Lines: 44

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.

>>    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?
>
>>   PhT - PhotoTransister (IR sensitive)
>
>They are known for being noisy and having low responsivity.
>A PIN photodiode costs several dollars.
>
   I wanted to be cheap, but I will look into decent parts.

>Good luck
   Thanks.

   Update:  I changed to a 1458 op amp (from a 353 BIFET).  This
is much more stable at high gains.  It still seems to be sensitive
to the volume control on the Radio Shack audio amp I connect.  Any
suggestions on how to match this to my circuit?  Thanks all.


-- 
Thomas Roden                                      | tom@syssoft.com
Systems and Software, Inc.                        | Voice: (714) 833-1700 x454 
"If the Beagle had sailed here, Darwin would have | FAX:   (714) 833-1900
come up with a different theory altogether." - me |