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Re: LF: False Decode or Real? - Opera vs opds

To: <[email protected]>
Subject: Re: LF: False Decode or Real? - Opera vs opds
From: "Graham" <[email protected]>
Date: Sat, 23 May 2015 21:28:14 +0100
Importance: Normal
In-reply-to: <[email protected]>
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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" <[email protected]>
Sent: Saturday, May 23, 2015 7:23 PM
To: <[email protected]>
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 <[email protected]>
An: rsgb_lf_group <[email protected]>
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

...








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