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From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <4F341AE5.1050704@talktalk.net> <C58324464DB74908908940561AD41698@AGB> <4F342525.1050200@talktalk.net> <A8B9B40838544BDD964CE6620E37E211@AGB> <4F34313C.1080005@talktalk.net> <1659D80990BC4B5482FF78B6249AACAF@JimPC> <6D99754E6FCA411DB4C678EC6ACFB9B1@AGB> <50F91B310A64456B9F2053865B66DB0B@JimPC>
In-Reply-To: <50F91B310A64456B9F2053865B66DB0B@JimPC>
Date: Sat, 11 Feb 2012 17:02:00 -0000
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Subject: Re: LF: Cats among pigeons
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All  noted  , Jim !

Bob  WE6XGR , is  running  a  OP2 / OP4   test  tonight (11/2)  from  00:00 
z , using  the  80 meter  settings, this  should  give  a  play off  2/4 
mode , then  we should  have the full  picture of  speed, as most  of the 
decodes  show  above the  OP2  limit.

Normal  service  should  resume this  Sunday  night ... I assume   'we' 
need  the  carrier levels to  be the  same  .. that  would  reflect  the 
most  'practical'  comparison .. (and  the  most  simplest !)

73 -G.



--------------------------------------------------
From: "James Moritz" <james.moritz@btopenworld.com>
Sent: Thursday, February 09, 2012 10:23 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Cats among pigeons

> Dear Graham, Eddie, LF Group,
>
>> There  is  3 dB gain  in each   X2 time  step
>
> One would expect so, but Eddie's results apparently contradict this. But, 
> if the transmitted signal power and noise power spectral density remain 
> the same, one would expect the indicated SNR to be the same also, 
> independent of the mode selected, since the SNR is referred to a constant 
> bandwidth (2500Hz), rather than the actual bandwidth occupied by the 
> signal.
>
>> I think  without using  path simulator  or  similar  these  are a little 
>> subjective ..
>
> This is certainly true; 3dB variation in either signal or noise level can 
> occur very quickly on 500kHz. Some time ago, watching G4JNT's WSPR beacon 
> on 500k, the signal level would sometimes vary by more than 30dB during a 
> single 2 minute TX period. That was in darkness over about 120km as I 
> recall; a shorter path during daylight might have much less variation, but 
> 3dB could still easily occur.
>
> What is needed is some independent way of determining the SNR during each 
> transmission. But a bit tricky when the signals are very weak. 
> Alternatively, transmit both signals simultaneously, from the same 
> transmitter, over the same path, and decode both simultaneously, which, 
> conveniently, Opera can do with some modes at least. This type of test 
> seems like a good application for the G0NBD dual-channel beacon...
>
> Cheers, Jim Moritz
> 73 de M0BMU
>