>-----Original Message-----
>From: Howard Winter [mailto:piclist-bounces@mit.edu] 
>Sent: 30 April 2005 01:37
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] RF encoding
>
>
>Mike,
>
>On Thu, 28 Apr 2005 15:36:11 +0100, Michael Rigby-Jones wrote:
>
>>...<
>> Initialy I was planning on using Manchester encoding to get a DC  
>>balanced bit stream and include a CRC to detect bit errors.
>
>Why are you worrying about DC balancing a radio system?  I can 
>see why you'd want to with cable linked comms, 
>but radio (especially if it's FM) really doesn't care about 
>it, as far as I know...

Howard,

The decision threshold of the data slicer is based on the average DC
value of the output data (imagine a comparator, one input connects
directly to the receiver output, the other connects to the receiver
output via a low pass filter).  A run of 0's or 1's will move the
decision threshold up or down and can cause large error bursts.  This is
true for both the cheap AM receivers and also many of the FM receivers
that use the demodulated output in the same manner.  One of the
functions of the preamble is to center the data slicer ready for the
real data.


>-----Original Message-----
>From: Alvaro Deibe Diaz [mailto:piclist-bounces@mit.edu] 
>Sent: 02 May 2005 17:24
>To: 'Microcontroller discussion list - Public.'
>Cc: 'J. Cardenal'
>Subject: RE: [EE] RF encoding

>I made an Excel sheet to make this calculations, but don't 
>know if it is allowed to attach it in a mail in this list, so 
>here goes a link to it:
>
>ftp://anonymous@193.144.52.77/pub/Codification.xls
>
>Regards,
>
>Alvaro Deibe Diaz.
>

Thank you very much for sharing your work.  I guess you used a simple
lookup table to decode your symbols into 7 bit values?

Regards

Mike

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