OK .. I see Jim replied to the reflector.
Hello everybody.
The rising and falling edges of the signal and how the associated four
corners are constructed, are the key to how much a CW transmitter signal
spreads, that is, clicks.
(see for example pictures A B C and D:
http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/CWShape.htm
)
The character set causes some variation to how much the CW transmitter
clicks in addition to also transmitting speed has its effect on the
sensation about the clicking.
The clicking can actually be measured using a SDR receiver, like Jim brings
up.
So, we have means to take this phenomena for real and deal with it by
engineering terms.
Within the CQ WW committee, we conducted a brief experiment on this subject
last Summer.
Transmitter site was my station, where I have a TS590.
TS590 has four CW keying settings 6, 4, 2 and 1, they control the rise time.
SDR receiver sites were in Europe and in U.S.
Path lengths were about 1000 and about 4000 miles.
Band was 20m.
Speeds of 30 and 45wpm were experimented.
Band width was analyzed at -30dBc and -40dBc levels.
The main outcomes were:
There is no difference in perceived or measured band width caused by
transmission path length.
(tested path lengths were about 1000 and 4000 miles)
TS590 setting 1 produced the widest spectrum while setting 6 was most
narrow.
Message that is transmitted i.e. the character set, affects the band width.
Speed at which the transmitting is done, affects the band width.
BW differences caused and measured, were several tens of percent.
For example sending a string of 55555 at 35wpm showed 310Hz at -30dBc while
a sending string of 00000 showed a BW of 130Hz at 35wpm.
Band width decreased 58% between 55555 and 00000 .
Keying rise time setting and speed were not changed - only the character
set was changed.
Speed change from 35 to 45wpm caused a BW change from 310Hz to 470Hz, that
is 52% increase measured at -30dBc.
Keying setting and character set were not changed - only speed was changed.
In case the CQ-Contest reflector participants would like to know more, I
can prepare a presentation of the experiment.
Maybe I could get a slot in WWROF presentations for sharing with the
community.
I would like to get a volunteer participating who would have a K3 or some
other radio that has been creating a lot of interest here on the reflector.
Also, the volunteer needs to have N1MM software so also the message under
test will be the same.
73,
Jukka OH6LI
su 15. marrask. 2020 klo 5.20 Jim Brown (k9yc@audiosystemsgroup.com)
kirjoitti:
> Yes, but the number of pulses per unit time doesn't describe the
> strength of the energy in each click when those clicks are the result of
> rise/fall time. When someone is clicking badly, or has excessive TX
> phase noise, it is the instantaneous amplitude, not how often the clicks
> or phase noise occur.
>
> My measurements, which are easy to duplicate with most SDR software,
> accumulates peaks in each FFT bin for a series of dits.
>
> Years ago, I measured my neighbor K6XX qs -49 dBC at 310 Hz from the
> carrier. He was running a K3 to a tube amp at legal limit. He and I can
> S&P within 500 Hz of the other running and perceive the other as simply
> a strong adjacent signal. Elecraft has been doing this since their K3
> was introduced in 2008, designed in 2007.
>
> -50 dBC at 500 Hz from the carrier is FAR too wide, and -50dBC is far to
> low a signal level to measure in a contest. I'd suggest something like
> -30dBC at a much narrower spacing, because it's far easier to measure
> under contest conditions.
>
> Another component of excessive bandwidth is transmitted phase noise --
> that "wooshing" sound present with keydown.
>
> 73, Jim K9YC
>
> On 11/14/2020 2:20 PM, Jukka Klemola wrote:
> > Bandwidth is about a signal level at, say, plusminus 500Hz off carrier.
> > Or it can be described as Hz off the carrier, plusminus, at a level, say
> > -30dBc.
> >
> > When there is one pulse per second, the side band shows a number of Hz
> > at -30dBc.
> > Making two pulses creates 3dB more for that particular amount of Hz on
> > the side band while the carrier is unchanged.
> >
> > If there are 4 pulses a second, there is 6dB more for the side band
> > signal at that same separation from the carier.
> >
>
>
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