[CW] CW Speed Limit ???

[N2EY at aol.com]

In a message dated 3/7/2005 3:35:11 PM Eastern Standard Time, "K0HB" <k-zero-hb at earthlink.net> writes:

>----- Original Message -----
>From: <N2EY at aol.com>
>
>> At 60 wpm, the theoretical on time of a dit is 20 ms. The rig described
>> will spend 5 ms on rise, 10 ms "on" and 5 ms falling for a 60 wpm dit.
>
>> At 120 wpm, the theoretical on time of a dit is 10 ms. The rig described
>> will spend 5 ms on rise and 5 ms falling for a 120 wpm dit, and only
>> an instant fully "on".
>
>Well maybe, but probably not.  This is a case where real-life trumps theory.

Yep. 

>Your examples depend on the unlikely notion that the 60WPM operator closes
>the key for only 15ms and the 120WPM operator closes the key for only 5ms to
>make a dit.

Ya won the kewpie doll.
>
>In real life, the operator will weight his keying to produce a 'pleasing'
>dit-to-space-to-dah ratio, taking into account the observed rise/fall times
>of his transmitter.

Exactly. Few transmitters, if any, adjust the rise/fall times with changing speed.

If the 60 wpm op closes his key 20 ms to make a dit, the rig described will spend 5 ms on rise, 15 ms "on" and 5 ms falling for a 60 wpm dit. If he makes a string of 60 wpm dits with the key weighted 50% on, 50% off, the rig will spend 5 ms on rise, 15 ms "on", 5 ms falling, 15 ms off, 5 ms rising again, 15 ms "on", 5 ms falling, 15 ms off, etc, for a string of 60 wpm dits. Bandwidth is the same but "copyability" may be different.
>
>> So the 5 ms rise/fall times do place a speed limit of sorts.
>
>And that speed limit is imposed by keyer >weighting and transmitter
>electronic design, not by FCC or ARRL edict.  

For now, anyway. If the "bandwidth proposal" goes
into effect, someone who chooses rise and fall times less than 3.75 ms may be cited for excess bandwidth - regardless of weighting or speed.

It >should be obvious from this
>discussion that an operator who wishes to transmit at 120WPM must fabricate
>a transmitter with rise/fall numbers much crisper than 5ms.

Exactly. 

Another point:

The shape of the keying characteristic makes a difference. The article linked by N1EA shows how the typical exponential curve characteristic has different sidebands than the error function characteristic - with the same rise/fall times. 

73 de Jim, N2EY