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Re: [CQ-Contest] SDR Mythbusters - ADC Overload myths debunked...

To: "Marijan Miletic" <s56a@bit.si>, "'cq-contest'" <cq-contest@contesting.com>
Subject: Re: [CQ-Contest] SDR Mythbusters - ADC Overload myths debunked...
From: "Mark van Wijk, PA5MW" <pa5mw@home.nl>
Date: Mon, 9 Nov 2015 18:29:05 +0100
List-post: <cq-contest@contesting.com">mailto:cq-contest@contesting.com>
Hi Mario,

My experience during many experiments is that weak signals just around or above 
the noise level, totally disappear on many DSP based receivers as soon as you 
switch from carrier to modulated carrier.

Apparentely  those DSP based receivers can detect/recalculate(?) a steady 
carrier in the noise, but contrary a modulated intelligent signal just 
dissappears.

73 Mark, PA5MW
From: Marijan Miletic 
Sent: Monday, November 09, 2015 4:29 PM
To: 'Mark van Wijk' ; 'cq-contest' 
Cc: 'rwmcgwier' 
Subject: RE: [CQ-Contest] SDR Mythbusters - ADC Overload myths debunked...

Mark, I thought for a long time that a carrier as a steady signal but in the 
case of ADC it overflows only at the short peaks and it can often be tolerated!

 

Weak signal can be detected by human operator with analog RX in the case of 
speech and CW.  DSP systems are much better in advanced modulations.  

Hams are amazed by HF PSK while EME in 21st century is done by WSJT with 
reasonable hardware.  It is easier for me to make RTTY LP QSO than CW L

DSP noise reduction greatly enhances weak signal detection due to human hearing 
abilities.  No way to do it with my beloved electronic circuits.

 

73 de Mario, S56A

 


--------------------------------------------------------------------------------

From: Mark van Wijk [mailto:pa5mw@home.nl] 
Sent: 9. november 2015 15:57
To: cq-contest; Marijan Miletic
Cc: rwmcgwier
Subject: Re: [CQ-Contest] SDR Mythbusters - ADC Overload myths debunked...

 

 

The NPR test is flawed because of its reference MDS.

 

MDS is measured using a STEADY carrier. 

As soon as you modulate a weak signal carrier, it  disappears in the band noise 
of most DSP/SDR based receivers where analog systems still offer a readable 
signal.

My measurements showed that analog receivers recover modulated signals at 5 - 8 
dB lower levels.

*****try measureing MDS with modulated testignals for a change *****

(a simple dit-dit-dit-dit as used in a S/N setup will do)

 

My conclusion: 

the MDS reference as a static benchmark does not resemble any real-life 
situation.

The calculated NPR figure is thus flawed; it does not relate to any intelligent 
radio communication reception.

73 Mark, PA5MW

 


<snip>


K9YC wrote:

>The Noise Power Ratio Test is especially problematic --

<snip>
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