[Elecraft] keying ration control

[Vic K2VCO]

dw wrote:

> Before rolling my own, I talked to one designer who provides updates for
> his keyer device.
> And he got all holier-than-thou on me when he understood that I wanted
> width control for all three elements.
> 
> My last cw rig utilizes the Curtis weighting schema and the dits were
> too short and the dahs too long.
> So with this adjustment schema, it was just not possible to get a
> satisfactory product.

In perfect CW, spaces and dits should be the same length. Dahs are supposed to be 3 times 
the length of a dit.

A weight control varies the dit:sapce ratio. Since most keyers base the length of dahs on 
the dits, it also varies the dah:space ratio.

It's not too hard to get a keyer to close a circuit with the proper ratios. The 
complexities crop up when you connect it to a transmitter.

Some transmitters shorten all keyed elements by a fixed amount, say 3 ms. If your keyer 
produces perfect code, then you will have two problems: both the dits and dahs will be a 
bit short (insufficient weight) and the ratio between the dits and dahs will not be 3:1, 
because the shortening is a greater percentage of a dit than of a dah.

The problem will get worse as speed increase because the shortening will be a greater 
percentage of both dits and dahs.

If you only have a weight control, you can't fix this. If you adjust it so that the dits 
are right, the dahs will be a bit long. Say the dit was supposed to 50 ms lon but the 
transmitter shortened them to 47. Then you adjust the weight control for 50 ms dits again. 
That means the circuit is actually closed for 53 ms on a dit, and 159 ms for a dah. When 
the transmitter shortens the dahs by 3 ms., they come out 156 instead of 150!

You could solve this by having separate adjustments for dit:space ratio (weight) and 
dit:dah ratio. But this would only work for a single speed.

The simplest solution is to implement keying compensation, where you can have the keyer 
add a fixed amount to each keyed element -- in this case 3 ms -- regardless of speed.

This is what the Idiom Press keyers do. In addition to a weight setting there is a 
compensation setting. You set the compensation to undo whatever your transmitter does, and 
then set the weight according to your personal preferences.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco