Topband: Key Clicks

[Paul Christensen]

K6SE:

> Therefore I have to disagree with the E-mails saying that the clicks are
> caused by overdriving/ALC (although this will surely accentuate the
> clicks).

Maybe this will change your mind...Here are the facts:  I just measured the 
CW rise/fall time on my IC-7800 at the point where the ALC region is just 
slightly active  The results:

Icom Setting                Measured

2 ms                            1.7 ms
4ms                             3.6 ms
6 ms                            5.2 ms
8ms                             7.0 ms

Next, I raised the drive level to 80% of the ALC range (Drive control at 
about 1:00)

Icom Setting                Measured

2 ms                            0.2 ms
4 ms                            0.5 ms
6 ms                            1.1 ms
8 ms                            1.5 ms

ALC has a profound effect on the IC-7800's CW rise/fall time and indeed, on 
most radios.

About eight years ago, I ended up modifying a Ten Tec Omni Six after the 
factory "Plus" upgrade.  Once distinct difference after the upgrade was that 
in an attempt to control a very slight amount of power overshoot in the 
original Omni Six, the Plus' ALC was redesigned by the factory to completely 
eliminate the power spike.  In doing so, the leading-edge rise time was half 
of what it was on the original Omni Six.  No amount of adjusting of the 
internal rise/fall control had much of an effect on the leading waveform 
edge.  Later Omni Six Plus units eliminated the control altogether and fixed 
resistors were used.  (i.e., why have a control if it no longer works as 
designed?)  Take a look at the QST product reviews for a comparison between 
the keyed waveform of the Six and Six Plus models.  I ended up re-designing 
my Plus with a 2-speed ALC circuit that held power spikes, yet left the 
ramped waveform intact.

For the measurements above,  I am using a microHam CW keyer modified with an 
isolated open-collector to +Vcc through a 1K limiting resistor for 
triggering an 80 MHz Tektronix SC 504 dual-trace scope.  This allows me to 
take reasonably accurate measurements without having to chase the waveform 
on the screen by changing the time base.  My measured points are taken at 
the point where the keyed waveform starts taking off and ending where full 
output is reached.

Paul, W9AC