Paul and all,
Back in the dark ages of the mid-40's I built the famous old "electronic
keyer" that had been in the Handbook for several years (page 141 of the
1946 edition). You know, the one with four 45 or 2A3 tubes in parallel used
as a switch to cathode-key an amplifier stage. The actual keying was
grid-block keying of the switch tubes with a small negative bias supply.
The unique feature of this keyer was the provision for independent
adjustment of the rise and fall times. Since all this was actually
implemented with RC circuits, the time functions were exponential.
With due care, one could obtain virtually any keying sound imaginable. With
very short time constants, the switching was virtually instantaneous with
accompanying clicks and thumps. But with adroit adjustment, a beautiful
waveform and sound could be obtained. Overdoing things would results in a
beautiful ringing waveform that sounded very much like a gong or sustained
bell!
As I recall I ended up with very close to the keying recommended in the
Handbook at the time. Without a scope (a 16-year old with a scope in 1947?)
I had to go by the sound in the receiver and compare it with the sound of
W1AW. I set up the keyer to sound like W1AW and that seemed to work well.
To get back to your point, I am almost certain that I had a very short rise
time, probably only a couple of milliseconds, but a fairly long decay time
that, like the rise time function, was an exponential discharge function. I
monitor all received audio with a scope and I observe an occasional CW
signal with the keying characteristics you desribe. However, the majority
of them are simply being switched on and off with fairly short rise and
fall times.
My Icom PRO, with its DSP generation of the keying waveform, offers only
the same rise and fall times over a range of from two to eight
milliseconds. I normally use two or three milliseconds in order to obtain
the slightly hard keying that I prefer. Thus far I have received nothing
but kind words about the sound of the PRO keyed signal, so evidently any
clicks are down far enough to be negligible.
Looking at the spectrum of the keyed signal, it is clear how much
difference the rise and fall times make in occupied bandwidth. At eight ms,
the bandwidth is proportionally narrow compared to two ms, but the keying
takes on that soft sound which is difficult to read in noise and QRM. In
neither case is the occupied bandwidth such that one would consider it
excessive.
And you're right, Paul, Mr. By and Mr. George had a lot of things figured
out which they well documented that still defy acceptance and understanding
by many of today's amateurs. Meeting George Grammer while I was in grad
school and visiting ARRL headquarters is still one of my favorite
recollections of those days.
I have owned two different C-Line stations and the keying of the T4X-C's
was very good, and in those days I did have a scope to monitor the keyed
wave form. It was a pity that the R4-C was not of the calibre of the T4X-C
without massive modifications, but I enjoyed using them nonetheless.
72/73/oo, George W5YR - the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771
Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437
All outgoing email virus-checked by Norton Anti-Virus 2002
Paul Christensen wrote:
>
> Some TR7s and C-Lines sound exceptionally good. I still recall the sound of
> Paul, K4CA who used a T4XC modified for QSK. I once looked at his waveform
> to see what was happening and it was a mirror image of what I described in
> the old handbook. What's interesting is that the decay looks nothing like
> rigs today. Instead, the decay drops sharply to about 50% of its maximum
> value then slowly decays out to about 6 mS. In other words, the wave form
> takes on the exact characteristic of a charging and discharging capacitor
> through a resistor. I found a 1940s QST article written by By Goodman, W1DX
> who designed a brilliant grid-block keying circuit whereby the individual
> wave form attack and decay controls were brought out to a front panel. He
> discusses changing the wave form to best match band conditions! Guys like
> By and George Grammer had it all figured out a long time ago...
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