Hi Markus, MF !
There are some more sources of signal-purity-problems :
Some high-Power PAs just use rectified mains supply (w/ or w/o
transformer). They do not use any linear regulation to stabilize the
very high output voltage. There only is a "suitable" capacitor at the
output of the power supply. I think this is one source of the 100 Hz
AM-modulation.
As you said, the original WSPR-software by K1JT is using
phase-continuous FSK modulation. But there is some substitute software
around that just adds one (WSPR-)tone to the next tone without any phase
relationship (I have had a look into the sourcecode). This will cause an
equivalent to key-clicks known from on/off keying modes. They are down
some 10s dBs but well visible on the waterfall.
The level of spurs at a DDS is mainly related to the number of bits of
their digital-to-analog output converter. Typical numbers are 10 to 14
Bits. A higher (input-)oszillator frequency of a DDS can enhance these
values to some extent if oversampling is possible and if it is used.
All these problems of purity become more visible with high ERP stations.
Those who can afford running such power levels should aim at optimizing
their transmitted signals in terms of purity, too.
Frohe Ostern & 73 de dg3lv Tobias
Am 27.03.2016 um 21:59 schrieb Markus Vester:
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)
*From:* Clemens Paul <mailto:[email protected]>
*Sent:* Sunday, March 27, 2016 8:47 PM
*To:* [email protected] <mailto:[email protected]>
; [email protected] <mailto:[email protected]>
*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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