Message-ID: <343F8C93278E4465B85099609E3ED1D8@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <AC666FAFFAF340258B396B3B6D0949A6@AGB> <8D2639CB5174D36-131C-D898@webmail-vm180.sysops.aol.com>
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Date: Sat, 23 May 2015 21:28:14 +0100
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Subject: Re: LF: False Decode or Real? - Opera vs opds
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Hi Marcus

Al last a  voice in the  wilderness  or is that  wilder beasts  :)

Yes everything  is  power , be it  noise or  signal  ,   I suppose  a signal 
is  simply a  refined  noise or it  would  not  have  a  bandwidth ..

There  will  always  be  a advantage  over  a  data  'decode'  , by  using 
correlation  as  one  is  required to  assemble  assemble   data  block's . 
then  by  logical  routine ,  recover the  original  data  , for  Opera 
that's  a minimum  of 40% of the  original  signal  , say  100  data 
block's , where as  the pattern  match . takes places over   40 % , 
effectively  summing  the  40%  to  increase the  recovered  power ,,,  then 
needing a  single  [final]  yes or  know  decision ..

I think  ultra stability  will  enhance the  Dynamic  system , but  as  in 
the  ''Ros House style''  it was  developed on simple  'ham'  kit , 
the   - 5 dB is  realised  in this  configuration .


The  gain could exceed 10 db ,  but  the  level  of  false  positives would 
be  'silly'  JR went  for  -5 dB , which  gives a  % false  equal  to  or 
better  than the   Opera  decoder  - unfortunately  , the  psk-map 
displays'  all  spots  , which leads  to  a certain  amount of  'excitement' 
the  web linked  windows  app  is the  ''only'' validated  out put  from the 
Dynamic mode ,

Note ,''tested at  op05''  the  opera  decoder's  are  linked to  band , 
with  set speed   , the  parameters  are not  the  same  for  all  the 
speeds , scaling  may  not give   compatible  results , Op05 is  the 
experimental  'flash' decoder ,  which is  giving  good  results  on vhf 
with  wide  spread  signals ,  where as the  OP8 and  OP32  are  configured 
in the  more  stable  [ zero spread]  lower  bands  ...

'' both  systems  reliably  produce   false detections ''

This is a  statement  of  fact  not  a  comparison, if neither  produced a 
false  out put  , then  it  could be  argued , that  the  minimum   -dB 
level  had  not  been  addressed  and the  design  requirement  to  ' dig 
out of the noise'  had not  been  achieved , other  wise  what  is the 
point ..  the  observed  problem  being , Decodes  = random call 
Correlation  =  valid  call ...  which  provides  endless  amusement ... :) 
.. From  observation , the  Dynamic  system  can be  seen  to  be  affected 
by  assumedly  band  or local conditions , some times  nothing , other 
times ,  more  than is  desirable , which , would  tend  to  suggest  its 
set  at the  optimum  ?

Both  use the  same  decisions ,  but  having  the  web linking  in place , 
JR   added  the  final  'dynamic'  check of  the  detection  'time'  while 
vetting the  call  lists , other  wise its a  stand  alone  system

73-Graham
G0NBD

Half steins or schnapps  :)


--------------------------------------------------
From: "Markus Vester" <markusvester@aol.com>
Sent: Saturday, May 23, 2015 7:23 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: LF: False Decode or Real? - Opera vs opds

> Hi Graham,
>
>> OPDS makes use of  Wolfs   some what excellent spectrum  software as
> DSP
>
> Spectrum Lab is used as the frontend for opds, the only signal
> processing done there is a straight high-resolution FFT before
> exporting the data. Opds then searches for spectral peaks, and
> transforms a 1024 bin channel around each peak back to time domain (0.5
> Hz wide, 4x oversampled). For coherent signals, the central carrier is
> extracted (including possible drift and fading), and synchroneous
> demodulation is performed. Then the resulting real waveform is Fourier
> transformed again for a CPU-efficient crosscorrelation to each of the
> callsign templates.
>
>> both  systems  reliably  produce   false detections  when  subjected
> to  noise ..
>
> Opds-32 has been running on LF continuously, typically analyzing about
> 20 QRM peaks every 10 minutes in a 115 Hz wide band. The searchlist has
> currently around 50 entries. With a correlation threshold of 15 dB, 28
> false detections have occured in 20 weeks since year 2015:
> https://dl.dropboxusercontent.com/u/26404526/opds32.txt
> In a pdf file distributed with Opera 1.5.7 software, the author EA5HVK
> mentions that he tested opds and got 11 false detections in only 4
> hours - an observation which is obviously not corroberated by my
> statistics.
>
>> hence  ultra stable  TX and  RX can give  advantage
>
> By using synchroneous demodulation rather than power detection, opds
> can detect coherent and stable signals that about 4 dB weaker. Attached
> are two plots, showing a side-by-side comparison of detection
> probability and SNR output from the Opera 1.5.6 decoder and the
> opds2h5c detector.
>
> SpecLab's digimode terminal was used to generated coherent and
> perfectly timed Opera signals, and white noise from the test signal
> generator was added with variable power density (dB/Hz). The very same
> output was analyzed wihin SpecLab to feed opds, and played to the Opera
> software usingh VAC. To speed up the experiments, all testing was done
> at Op-05 speed (30 seconds), and SNR values were then scaled down by 24
> dB to Opera-32. During the test, no false detections were observed in
> the output from either program.
>
> In the attached splot uccessrate.png, the solid lines with squares show
> detection probability (0 to 100%) against average SNR in 2.5 kHz. The
> classic Opera decoder (red) achieved 50 % detections at -40 dB. Opds
> correlation (blue) goes down to -49 dB, showing a 4 dB advantage for
> these ideal signals. The blue crosses indicate correlation dB output
> from opds - note that only hits above the standard 15 dB threshold
> (dashed line) were counted as successful detections.
>
> SNR_output.png shows indicated SNR values versus actual SNR from both
> programs. Opera 1.5.6 seemed to consistently read 1 dB high, whereas
> opds reads approximately 1 or 2 dB low, with a larger scatter. Part of
> this negative offset is because I had originally assumed the "dBOp"
> scale to be referenced 4 dB (instead of 3 dB) below PEP.
>
> I have not yet tested the dynamic deep search in Opera 1.5.7, but the
> claimed -45 dB threshold (ie. 5 dB better than the decoder) seems quite
> plausible. I believe opds is also around 4 dB less sensitive for
> non-coherent signals, which would then put both programs in same
> ballpark.
>
>> Now mines a  pint  or  are we onto  shorts  now ?
>
> Please explain...
>
> All the best,
> Markus (DF6NM)
>
> -----Ursprüngliche Mitteilung-----
> Von: Graham <g8fzk@g8fzk.fsnet.co.uk>
> An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
> Verschickt: Sa, 23 Mai 2015 4:48 pm
> Betreff: LF: MF 630m: False Decode or Real?
>
>  intelligent  life in other Galaxy's ?  Like the  Bar ? 11:14 . Suns
> not
> over the  yard yet .. Tad early  Eddie ?
>
> Armature radio V  Armature  hour , take 2
>
> Opera  MF and LF  is a BOGOFF  mode , Buy  one  and  get one  free ,
> just
> that  its free  to  uses and the first  is a data  mode  the   second
> mode
> is  a correlation  system , dynamically  engaged ..  page 70  seems  to
> miss  this  rather  important  fact along with  the  design  solutions
> embodied  therein , I'm waiting  for  page 71 ..
>
> The  test of a good design  is that no one  notices , it just works .
>
> In  that  24  hour  window ,  Opera  LF produced no  false  data
> detections
> or  false  dynamic  detections , where as  the  wspr  system regularly
> fills the LF map , a simple  test of design , preventing  false
> correlation
> detections  is more  difficult  than  false data .  Opera  LF is  -40
> dB
> and  -45 dB  ... that  well  cool as  J C would (of) said
>
>
> Now the  tacky bit
>
> As Im sure  Markus  will  tell,  OPDS  and   Dynamic   share the  same
> design criteria
> To  drag  low  signals  out  of noise , by pattern  matching , OPDS
> makes
> use of  Wolfs   some what excellent spectrum  software as DSP  , whilst
> Mr.
> Ros  uses his  own  designs .  both  systems  reliably  produce   false
> detections  when  subjected to  noise .. not all  the  time ,  just
> depends
> on the  detection monkeys sense of humour on the  day.
>
> The  design  solutions'  branch ,   OPDS  makes  accurate  frequency
> measurement and  Bandwidth , along  with allowing  parameters to  be
> adjusted by  the  user ,as  well  as  maintaining  the  look up  table
> hence  ultra stable  TX and  RX can give  advantage .. And as  pointed
> out
> , presents  the  user  with a  set of  parameters, which may be  used
> as
> validation
>
> Opera Dynamic retains the  Plug and  Play  house  style , yes these are
> criteria , but  are evaluated by the  system  , load it  and  it dose
> the
> rest ,  Opera  data  runs  as  normal ,  Opera  dynamic  is  engaged
> should
> the  decoder  fail , the  sever handles the  validation  and  maintains
> the
> list.
>
> Both  systems OPDS and  DYNAMIC   produce  false  real  hits ,  Dynamic
> take
> things one step on, where wspr  uses the  internet as  part of  the
> DSP
> sync . Opera Dynamic  uses  the  internet  to  pool  ' recovered time'
> data
> and  validate the  spots by  identity and  coincidence of  time ..
>
> Now mines a  pint  or  are we onto  shorts  now ?
>
> 73-G
>
> ...
>
>
>
>