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Re: LF: WSPR sidebands

To: <[email protected]>
Subject: Re: LF: WSPR sidebands
From: "Graham" <[email protected]>
Date: Sun, 27 Mar 2016 22:01:07 +0100
Importance: Normal
In-reply-to: <[email protected]>
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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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