Hi Lee,
I see what you are describing now, and it should be clean CW.
Waveform is VERY important, more so than rise and fall in most
cases.
I'll try to do a better job of explaining, because I still some of us
assume we can hear a raised sine or filtered waveform as a "soft"
start.
> OK........getting back specifically to the keying characteristics of
> the PJ's, perhaps I should have explained how I measured the rise and
> fall times. I used a long standing standard for measuring pulses of
> timing the slope between 10% and 90% amplitude, and then I rounded it
> to the nearest full millisecond. I did not think we were into
> splitting hairs here. Beside, I have not calibrated my 'scope
> against a traceable standard lately so I do not know how the error it
> may be contributing.
The problem isn't splitting hairs.
The problem is we are trying to verbally describe something that is
almost impossible to look at and decide if it actually clicks. One
difference is I use the starting and final points of both the rise time
and the fall time because that is what concerns us in switching
times and bandwidth, and you are using the 10% and 90% levels of
each.
I'd like to go back to the point I made earlier. We can not tolerate a
fast turnover in slope at any point in the waveform. That would
include points below 10% and above 90% amplitude!
We should suppress sidebands (clicks) outside the normal
bandwidth of our receivers at least 50dB, and more if we are
parking next to weak signals. The typical range of signals at my
house measures about 60-70 dB, and at times it approaches 80dB.
You can't reach that level of attenuation with the type of waveform
shown in the Handbook, because if you look at the waveform
carefully you will see sharp slopes at the very start of the rise, and
the very start of the fall. We have to be very fussy what we do in a
radio, otherwise we will bother people.
A good start is to use a 5mS (total) rise and 5ms or slightly longer
(total) fall time, and if you use a sine-shape (error function or
similar) you can get a bit faster and not have problems.
Sharp slopes don't make a pleasant "sound", they cause clicks.
They are too brief to make it through the filters of anything but a
very wide receiver filter. We will never even hear those "clicks"
unless we are tuned off to the side of the signal, and the only thing
they do there is cause QRM!
What has been described here as "desirable" is actually the
waveform Kevin describes as an exponential waveform and I
describe as "single-pole R/C filtered" waveshapes. This is the
shape provided by FT1000's as well as those old grid-block keyed
rigs, it is the result of filtering the modulation (a square wave from
the key) in a simple R/C circuit. The result (harmonics and all) then
AM modulates the carrier.
> More importantly, the keyed CW pulse looks very much like the
> "error function" turn on described by Kevin Schmidt K9CF in his paper
> found at:
The shape I call a "filtered dot" is nearly identical (nothing is
perfect) to Kevin's error function. If it has the shape or a similar
shape as Kevin describes it is also known as a "filtered dot". Again
what we can not tolerate is a sharp bend or steep slope at any
point in the waveform.
> Kevin goes on to say in that paper "...For a given rise time, the
> error function shape for the rise and fall will attenuate unnecessary
> interference away from the carrier frequency much better than
> exponential keying..." Hence, the PJ's, while having maybe a little
> less than some arbitrary ideal rise time, have the ideal wave shape
> which leads to minimizing key clicks. See the paper referenced for
Indeed! Also the sound will NOT be too soft. The point I try
(unsuccessfully so far, hi hi) to make is when filtering is set for a
reasonable bandwidth you get something similar to a raised-sine
shape, a waveform without abrupt changes in slope at any point
from zero to full power.
There is no possible way any of us can "hear" a few cycles of a
500 Hz or 800Hz tone as a "soft" rise and fall, because the period
is too short for the ear and brain to register. Even if your ear and
brain worked that fast, the receiver would not permit it when using a
normal CW filter.
If you want an example of how you "hear" a few cycles of a tone,
tune in WWV and look at the seconds "tic" on a scope. The "tic" is
a perfect sine-wave tone (I think it is a 1000Hz tone).
> a full discussion. One can confirm that the PJ's do not create
> excessive clicks by doing a fairly simple test. Connect the radio to
> a dummy load. Loosley couple a clean, quiet receiver like a
> CorsairII such that the keyed signal of the radio under test produces
> a 10 to 20 over S9 signal. Send a series of dots with the
> transmitter being tested. Switch in the narrowest filter in the
> receiver and tune around the signal. If there are any troublesome
> clicks, you will hear them. I did just that a few minutes ago and
> found NO key clicks anywhere on the band. I did have some phase
> noise close in as expected, but no key clicks
Actually that is the best test possible, because you are looking at
the signal the way the receiver and ear looks at the signal. My web
site describes that method in my tests, except I used both a
receiver and a peak detecting selective level meter with sample and
hold.
Every radio should be tested that way.
It is possible to actually have a rise and fall and shape that looks
perfect, and have bad clicks! It is not possible to have an
excessively short rise and fall and not have excessive bandwidth,
however.
But now that The waveshape and times are described in more
detail, the "PJ" certainly has the potential to be what for all
purposes is click free...and with that rise and fall time, it should not
sound too soft either.
73, Tom W8JI
W8JI@contesting.com
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