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Opera's AM key-clicks ,
VERY True , there has to be an associated bandwidth,
however , hard non-conditioned on off keying
of a carrier will produce , key-click's , this was
the subject of a e-mail , sent to me some time back,
over my TX bandwidth on 477 /op8 .
Notably , the email enquired as to how my Tx
b/w was in the order of 10 MHz or less and
not the mode usual 400 / 500 MHz
Its quite simple, I use the audio drive
, via a totally linear TX path ma1723 >
skanti amp
What appears to be a simple task, is often
quite complex , as is the use of the R-PI as a rf
carrier source
The integrity of the timing loops [ as
before] are compromised by the higher order IRQ
requests , hence setting a flag
high/low , with a executed code routine to
generate a 'stable' carrier source cannot be relied on.
In the development of the Opera R-PI tx code ,
the action of the IRQ's could be observed as
random noise , acting cycle by
cycle , hence any long persistence in the spectrum
plot , simply masked the spurs , however , the Opera
dsp returned varying s/n levels for the same
test set up , indicating the channel background noise varied.
[ opera decoder is a sampling system running far faster than
the data rate ]
The project was shelved , other than for hard
on-off keying of a free running carrier , in
this the clock jitter is of no consequence.
73-G,
Sent: Sunday, March 27, 2016 8:59 PM
Subject: LF: WSPR sidebands
Hi Clemens,
the 1.465 Hz spaced lines around the strong WSPR
signals are "clicks" from the periodic frequency switching, they are
supposed to be there. But as the switching is phase-continuous, these FSK
sidebands fall off much more rapidly than Opera's AM key-clicks.
The 100 Hz lines should normally disappear if a
properly regulated ripple-free power supply is used for the TX. Has
DJ0ABR rechecked the voltage ripple after the change?
But there may be other subtle causes for
low-level 100 Hz modulation both in the TX and RX
chains, e.g.
- hum injection into PLL oscillators causing phase
modulation,
- ground impedance modulated by the rectifier
diodes in the power supply,
- modulated scatter from traditional flourescent
tubes (more at VHF though), - noise blanker acting on
periodic interference (eg. SMPS or PLC),
- hum injection into the audio chain.
Spurs from the DDS would not be impossible but
usually at lower level, and unlikely to exactly hit 100
Hz.
Best 73,
Markus (DF6NM)
Sent: Sunday, March 27, 2016 8:47 PM
Subject: RE: Cheap and nasty sources - was LF: DK7FC WSPR bad
quality problem
Hello
all,
I've been watching the 100Hz sideband WSPR multi-decodes also from
the other two strong stations on MW,
DH5RAE and DB0ABR.They are located about
65km from me and generate S9++dB signals here.
The deoded sidebands are
also about 40dB down.
DB0ABR has tried a different power supply to no avail
and both believe that the DDS synthesizer is the culprit.
It is a
AD9859,see
http://www.dj0abr.de/index_english.html
I
have added a perseus screenshot with a bin width of 0.24Hz showing strange lines
in their signal.
I'm not sure if this is the DDS spectrum what we see
here.
73
Clemens
DL4RAJ
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