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

[Mark van Wijk, PA5MW]

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 at 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

 


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K9YC wrote:

>The Noise Power Ratio Test is especially problematic --

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