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References: <4F154949.10262.2B953A@mike.dennison.ntlworld.com>
Date: Tue, 17 Jan 2012 10:45:38 +0000
Message-ID: <CAA8k23TVsaEv0Wer+rBz298R=GMM6TH473tP2T8kmq1zohq51g@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Opera reception
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dB Signal to Noise, referenced to the amateur 'standard' 2500Hz
bandwidth - approximating to an SSB or voice bandwidth
Originally sort-of defined by Joe in WSJT.

For an experienced Operator, SSB can be received in 0dB S/N and CW in
about -5 to -10dB (again in this BW)

For any data mode, divide the actual decoding or noise bandwidth (not
the width of the transmitted signal) into 2500Hz and take 10.LOG the
result to see the normalisation process.

So if you use OP2 with its 0.5s symbols and noise bandwidth, a report
of -25dB means in reality 10.LOG(2500 / 0.512) - 25dB = 11.8dB above
actual noise.    So a good strong decodable signal, that you wouldn't
hear.

A value of 'about' 3 - 4dB above actual noise is needed for decoding
this mode. (And that's mean power.   Half the peak Tx on)

Andy  G4JNT


On 17 January 2012 10:11, Mike Dennison <mike.dennison@ntlworld.com> wrote:
> Having found a battered old laptop running XP and with a COM port, I
> started to set up my Opera station yesterday. I could see a good
> signal but spent hours messing about with sound card settings trying
> to get it to decode. Finally I discovered that Opera had changed yet
> again and new (incompatible) modes had been introduced. Grrr!
>
> After reluctantly joining the Yahoo group (yet more emails to read),
> I downloaded yesterday's version (1.1.1) and decoded G4JNT (-4dB),
> PA0A (-14dB) and RN3AGC (-35db at 2120, and all night peaking -21).
> What do those dBs represent? Presumably some kind of SNR.
>
> I am trying hard to support this mode as it suits my station very
> well, but there are many aspects which are very frustrating, which is
> a pity.
>
> I now need to find an adaptor to convert my Tx system's 25-way D plug
> into a 9-way for the laptop. Then I will be transmitting.
>
> 73 de Mike
> ========
>