Hoho,
Well,over the years I have "assisted the court" as an expert witness dealing
with just these issues, and yes, some of my best friends are......
The burden of the tale is that a dB is a more or less constant ratio between
two signals that is needed to before one can be judged stronger or weaker
than the other, independent of the signal level.
These statements imply a more or less unidimensional "pure tone" signal.
The situation of picking out specific signals from an S7 roar is a lot more
complex, and you are right to say that a dB more or less is of little
account. Psychophysics can handle this with more elaborate models based on
Signal Detection Theory, however. And SDT works for machines as well as
people, so the convergence of psychology and physics is pretty good in this
area.
If we go back to the simpler cases, then a dB will make all the difference
in working weak signal cw, for example. Hence the obsession with single dBs
not so silly. For normal DXing one dB will result in a significant
improvement in countries worked over a period, even if the effect is not
readily observable on any single QSO.
Another angle: 3dB = doubling tx power. It is not impossible that the
cumulative effect of putting in a better feedline, stripping and cleaning
joints in a beam etc etc could add up to as much as 3dB, ie equivalent to
doubling power. Hence the obsession over dBs may not be all that silly.
And when the operator believes that everything is going as well as it
possibly can, he/she is more confident and likely to be a better performer
regardless.
Great on Palmyra. One of many islands I have yet to visit.
end
73
Barry Kirkwood PhD ZL1DD
Signal Hill Homestay
66 Cory Road
Palm Beach
Waiheke Island 1240
NEW ZEALAND
www.waiheke.co.nz/signal.htm
----- Original Message -----
From: Stu Greene <wa2moe@doitnow.com>
To: Barry Kirkwood <bjk@ihug.co.nz>
Sent: Friday, 07 September, 2001 1:15 PM
Subject: Re: [TowerTalk] Re: [AMPS] True Or Not True #2
> At 12:24 PM 9/7/01 +1200, you wrote:
> >See Stevens, S.S. Handbook of Experimental Psychology.
> >If this is psychobabble then so are physics texts.
> >cheers
>
> Barry -- I'm a solicitor/barrister and you're obviously a psychologist and
> never the twain shall meet.
>
> I've done plenty of dxpeditioning as well as dxing, and simply put, I want
> to hear. I suspect that at my age if I am unable to hear a voice or a
> Morse character, an increase of transmitted power of one decibel would
make
> no difference.
>
> In no way am I jesting any longer. This thread has become ridiculous. I
> will readily admit that three decibels make a strong difference -- that's
> half an S unit on a calibrated receiver; possibly two. But if I'm at the
> other end of a pile up, I promise I will work stations with strong signals
> (power, propagation, antennas) and I will work dirty stations to get them
> out of there.
>
> I remember on one occasion I was the sole phone operator on Palmyra in
1988
> looking for Europe. I worked the strong stations and then there was a
> steady S7 roar over the twenty kHz I was scanning. I could not pick out a
> single phonetic. And that one dB would have been lost in the shuffle.
>
> As a practical matter, I feel that operators spend far too much time and
> money to capture that elusive decibel and, Barry, in the real world ...you
> know the rest
>
> A nice day and 73
>
> Stu
>
>
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