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

[Andy Talbot <andy.g4jnt@googlemail.com>]

---------- Forwarded message ----------
From: Murray Greenman <denwood@orcon.net.nz>
Date: 22 August 2010 09:01
Subject: Fw: LF: Fw: Covert Char per Min to Words per Min ?
To: Andy Talbot <andy.g4jnt@googlemail.com>

Andy,

Perhaps you can forward this on to the lf group...

 

I'm sure your calculation for CMSK8 is correct, although with a varicoded system it is highly dependent on the average character length. What I actually did to determine the speed was to measure it sending 'Quick Brown Fox' over a five minute transmission.

 

I would convert CPS to WPM by multiplying by 10. There are five letters in the average word, plus a word space, so 1 char/sec is 10 WPM. Char/min is CPS x 60, of course.

 

CMSK8    3.75 WPM, 0.375 CPS, 22.5 Char/min

CMSK31    15 WPM, 1.5 CPS, 90 Char/min

 

and so on.

 

73,

Murray ZL1BPU

 

 

----- Original Message -----

From: Andy Talbot

To: rsgb_lf_group@blacksheep.org

Sent: Saturday, August 21, 2010 8:19 AM

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

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?

 

Andy
www.g4jnt.com

On 20 August 2010 19:09, Graham <g8fzk@g8fzk.fsnet.co.uk> wrote:

 

From: G ..

Sent: Friday, August 20, 2010 6:16 PM

To: rsgb_lf_group@blacksheep.org

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