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Re: LF: Fw: Covert Char per Min to Words per Min ?

To: [email protected]
Subject: Re: LF: Fw: Covert Char per Min to Words per Min ?
From: Andy Talbot <[email protected]>
Date: Fri, 20 Aug 2010 21:19:40 +0100
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Normally you can assume 5 characters per word, that factor is is reasonably constant - the average word is 5 letters
 
The number of bits per character  is more complicated to quantify.  In  CMSK for example,  where the character length varies based on the probability of the letter's occurence in typical messages, the effective number of bits per character is less than for ASCII encoding, say around 5 or 6 bits per character average for the whole alphabet.   With a heavily source encoded scheme - like WSJT with a small alphabet to start with, - it is possible to get right down to less than 5 signalling bits per character.  But particularly in Varicoded data, there are more bits added in framing and synchronisation, so call it total of 7 bits per character complete
 
If you then take note of the error correction overhead, which doubles up the number of bits sent for each message, and add in another 17% of synchronisation bits , you end up with a net rate of something like 17  bits per character for the error corrected message.  So, CMSK8 (8 bits per second) equates to about 8/17 characters per second, or 30 characters per minute, or 6 words per rminute - which is rather faster than the 3.75 rate quoted in the table - so I've missed something somewhere?
 
CMSK8 is 8 times faster than CMSK1, but its not the whole story.   If the link is too weak to support the faster speed, but the slow one gets through - which is then faster ?   CMSK8 that may work tomorrow, if you're lucky, eventually;  or will work CMSK1 now?
 
On 20 August 2010 19:09, Graham <[email protected]> wrote:
 

From: G ..
Sent: Friday, August 20, 2010 6:16 PM
Subject: Covert Char per Min to Words per Min ?

Q How  do  you  convert between   Characters  per minute and Words  per Minute
 
is  CMSK-8 data rate  faster than  MF-1 ?
 
Tnx - G.
 
 
CMSK8 7.8125 12.5Hz 3.75 WPM 12H5F1B
CMSK31 31.25 50Hz 15 WPM 50H0F1B
CMSK63 62.55 100Hz 30 WPM 100HF1B
CMSK125 31.25 200Hz 60 WPM 200HF1B
 

ROSMF1: 16.7 characters/minute
ROSMF7: 128 characters/minute



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