Message-ID: <2000041511023268199@zetnet.co.uk>
Date: Sat, 15 Apr 2000 11:02:32 +0100
To: rsgb_lf_group@blacksheep.org
From: "Peter Dodd" <g3ldo@zetnet.co.uk>
Subject: Re: LF: Slow CW Sensitivity Measurments
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Hello Geri

> I made some laboratory tests this morning to get some indication about the
> ability to communicate with signals below noise level using Slow-CW.

A most interesting set of measurements. Most of us who use this mode 
felt that an it gave an extra 15 to 20dBs but this is the first time 
I have seen objective measurements.
While not giving the same noise improvement described in the 
pionering work of G3PLX and G4JNT described in the LF Experimenter's 
Book, Spectrogram and Spectran does provide a convenient compromise 
that can be managed by us non-techies.
I have made some improvements to the antenna and although this gives 
me an extra 0.5Amps on transmit, the downside is that it has 
increased the level of the Loran sidebands. While the strength of 
each of these sidebands is not that high the effect of several 
hundred of them in a passband of 2.7kHz holds the S-meter at S9! 
While the fix would be to use a directional receiver antenna, such as 
that used by Laurie or Derek, with QRSS it is not necessary because 
of the ability of this mode to read signals between the Loran lines. 

> I would be interested to get your comments or own measurements on this
> subject. I do not yet have sufficient experience with Spectran to make full
> advantage of this software, so I would like to hear about that software as well.

During the month of tests receiving the 20mW erp from I5TGC over an 
1800km path (plus Alps) I found Spectran had a slight advantage (even 
at its Beta stage) mainly because it has a higher frequency 
resolution. I used the 0.125Hz setting which placed the Loran 
sidebands (on average) about 15mm apart, which gives plenty of space 
to see a signal. The best compromise dot period for 0.125Hz apears to 
be around 5 seconds.

At this stage the Speed Control (integration time?) is not slow 
enough take advantage of the 0.064 and 0.032Hz settings of Spectran. 
It would be interesting test these narrower settings to find the 
limit of the soundcard.

Geri, I would be most interested in any tests you may make on 
Spectran - I take it you have a copy.


-- 
Regards, Peter, G3LDO

<g3ldo@zetnet.co.uk>