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Hi Stefan,
> If my clicks would be reduced, would then the
NB performance come back to 100%?
No. These are two separate effects. The
keyclicks are actually a part of the transmitted spectrum, wheras the NB
artifacts originate in the receive processing. What they have in common is that
they create a "near-far" problem by limiting the dynamic range, even if the
receiver and soundcard are otherwise perfectly linear. The point I was
trying to make is that we should try to separate operating frequenencies
of simultaneous local and DX operations by at
least one kHz.
Now in summer the noise
blanker effects (spectral widening
of intrinsically pure carriers due to the chopping, and increase
of noise blanker threshold) are the bigger problem. They could be
mitigated by inserting a software bandpass which excludes
the local signal. But if the frequency of that
signal is too close to the desired signal, the bandpass has to be
narrow and steep. This unavoidably prolongs the spheric impulses and
renders the NB less efficient. Even at times without lightning QRN, the NB
is needed here to suppress the nasty FSK telegram sidebands from our big
brother DCF-39. This also doesn't work well when the pulses are
prolonged.
To minimize the bandwidth of the transmitted
keyclicks, the rampup and rampdown times should be a significant part
(eg. 25%) of the symbol duration. Eg for Op-32 (8 second dashes) you
could make it as long as 2 seconds, which will contain most of
the power within 0.5 Hz. Using a low-pass filtered com-port
signal to modulate a continuous carrier is certainly a good
solution. The filter hardware could be just a couple of
RC networks, preferably with switchable time constants for
different speeds.
Software ramps are also a good option, but as Wolf
says you will need an (at least somewhat) linear transmitter. Using
SpecLab's signal generator with an arbitrary waveform modulation produces
nice band-limited output. With the inbuilt samplerate correction you
can even produce a GPS-derived audio carrier. You will have to prepare an
ASCII wave file by editing the Opera 01 sequence for your callsign. As an
alternative standalone option, I have been using Wolf's little SndOutpt
tool, which can upsample an Opera IQ waveform with excellent
interpolation.
Sent: Friday, August 31, 2012 1:47 AM
Subject: Re: LF: Opera frequency
usage
Am
30.08.2012 17:09, schrieb Markus Vester:
> [...]
> - DK7FC was
active on a nearby frequency during most of the night. In
> conjunction
with the noise blanker the RX is desensitized by the a
> nearby strong
signal. The problem is exacerbated by high density of
> keyclicks in
Opera (5 to 8x more than QRSS), and that most seem to
> apply hard
keying. Trying to interleave operating times (eg. even vs
> odd days, or
hours) is probably not a satisfactory solution.
Sorry for that Markus. You know, the AM
modulator is very near to the
top of my Todo list and the first half of the
circuit is working now
(BTW not using a PWM with a TL494 but a VCO using a
CD4046. That works
well). So it sould be possible for me to reduce key click
of signals
generated in SpecLab, i.e. QRSS/DFCW/HELL/Beacon-Cw, soon. If my
clicks
would be reduced, would then the NB performance come back to
100%?
However Opera directly keys the PA using the COM port and an
external
signal generator (SL!). This is one of the main advantages of that
software and why Graham calls it CW replacement mode (of course CW
cannot be replaced, it is a language for its own).
Recently we
discussed about transmitting the OP code by playing an image
in slow hell.
Or alternatively a file which can be loaded ito the
arbitrary waveform
generator of SLs signal generator could play the code
in SL. Of course the
software could be run simultaneously. Maybe even
the Opera TX-button can be
virtually pressed by a DOS command so the
announcement of that transmission
is is sent to the web? The mode and
band information must be sent too, to
coordinate the software with the
actual TX then. That makes it more and more
complex.
So what might be the solution for those who use an external signal
source and just key the PTT by the COM port using Opera software? Maybe
a special higher order shaping using hardware, like in a CW HF TRX?
Possible!
73, Stefan/DK7FC
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