From: "Mike Dennison" <mike.dennison@ntlworld.com>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 01 Dec 2010 14:36:18 -0000
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Subject: LF: QRSS120 and grabbers
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A recent message said that JA7NI needed a way to display more 
spectrum on his Argo grabber set to QRSS120. I posted a reply 
recommending SpecLab.

This raises another issue that has concerned me for some time. There 
is a tendency for DX grabbers to be set to QRSS120, and quite a few 
beacons use that speed, or even QRSS240. Indeed if the target grabber 
is set for QRSS120, the transmit station must use at least this dot 
length to be read successfully.

I believe the danger is to regard this as the 'optimum' speed for DX 
working, simply because the S/N ratio is good. In practice, there is 
another factor in play. There is often rapid and deep fading on a DX 
path, often resulting in only parts of letters being received at this 
speed, even though the peak signal is quite strong (see many of the 
pictures of transatlantic reception regularly posted on this group).

The situation becomes worse if the final aim of experimenting with a 
path is to have a two-way DX QSO. Even exchanging minimal 
information, a QSO will take several hours, during which time the 
conditions must hold up. Take a look at VE7TIL's excellent DCF39 
graph to see how short a good DX opening usually is - perhaps an hour 
if you are lucky. 

The very few who have had transatlantic QSOs have used QRSS30 or at 
most QRSS60. I am not aware of a successful two-way involving a 
longer dot length.

I would suggest that DX beacons and grabbers use a =maximum= of 60s 
dot length (though a second grabber screen could be provided for 120 
etc if desired). In my opinion this would be more likely to result in 
useful propagation data.

Any thoughts?

Mike, G3XDV
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