[ARC5] dB Power and QRP according to HR magazine. [Was dB - Apples & Oranges]

Wed Oct 30 16:11:58 EDT 2013

I have made some unofficial measurements on my home station in the past in
which a quality well-shielded signal generator feeds the receiver via a lab
grade step attenuator.  Using the receivers own white noise as the
background, a 1dB change is easily detected and the change definitely
impacts copy.  When the generator output is summed with antenna noise to
simulate a similar weak signal condition, the 1dB step is still discernible
but the character of the real-world antenna noise (high peak to avg ratio)
does not permit as significant an improvement upon copy.  If one tosses in
the ionospheric modulation of a real signal (vs a steady pure note) I doubt
the 1dB makes much of difference at all; the change gets lost in the other
more significant variations going on.  I concluded the situation is worst
for HF DX over the poles.  Correspondingly, the best situation is probably
for weak VHF line-of-sight CW where the background noise is more Gaussian
in nature and an unsteady ionosphere is not coloring the signal itself.

Having said all that, I do still work hard to keep my feedline losses under
1dB :-)

Dennis AE6C

On Wed, Oct 30, 2013 at 12:08 PM, Bruce Long <coolbrucelong at yahoo.com>wrote:

> hello all
> I had a human sensory perception course in college and in that course i
> was introduced to the concept of a JPD-- Just perceptible difference, ie
> the smallest increase or decrease of a sensory stimulus that was detectable
> as a change.  of course the JPD is depends upon a lot of factors which  for
> audible JPD as was pointed out earlier in this string includes tone
> frequency spectral purity, amplitude observer motivations and many others
>
> My personal very rough rule of thumbs are
> 1 dB is about 1 JPD for experienced motivated observers  ie CW ops
> 3 dB is about 2 JPDs for experienced ops or 1 JPD for motivated but
> inexperienced observers-- ie ordinary people not hams/cw ops
>
> 8-10 dB produces the impression of a doubling or having of an audible
> stimulation'
>
> Seeing as the amplitude response of human hearing is logarithmic such
> numbers and ratios are sorta- kinda- correct.
>
> bruce
>
>
>
>
> On Wednesday, October 30, 2013 2:36 PM, Leslie Smith <vk2bcu at operamail.com>
> wrote:
>
> >"I believe it started as saying 1dB is too small of a change for the
> human ear to detect and morphed to become
> > 1 dB is the minimum change that the ear can detect.  This sort of
> morphing is common."  - Bill
>
>
> Hi Bill
> I see you understand the process that barristers (an Australian
> high-level lawyer) use in court during cross examination.
>
> Years ago an article appeared in "Ham Radio" magazine relating the
> ability of a human ear to detect a change in sound level.
>
> The article was quite interesting - even though the measurements were
> done on an informal basis using only uncalibrated equipment that might
> be found in a well equipped "ham" shack.. After a half-hearted search I
> couldn't find the article, but it was definitely published by "HR".
>
> If my memory is correct the author of that article found the change in
> power (i.e. dB) was greater than the figure most have quoted in this
> thread, and well above 1 dB.  The article drew the conclusion that under
> good conditions a 5 or 10 watt QRP transmitter may make effective DX
> contacts - and that a 100W or 400W signal might be heard 'better' but
> that QRP was still worth-while.
>
> Some will criticize the method, some will criticize the equipment but I
> applaud the idea of doing the work and observing the result.
> My observation is this:  "Knowledge gained by personal effort is often
> of a better quality than knowledge gained by other means."
>
>
>   73 de Les Smith
>   vk2bcu at operamail.com
>
>
> On Thu, Oct 31, 2013, at 2:47, Fuqua, Bill L wrote:
> >    I believe it started as saying 1dB is too small of a change for the
> >    human ear to detect and morphed to become
> > 1 dB is the minimum change that the ear can detect.  This sort of
> > morphing is common. An example, my wife
> > was told that adding green beans to our dogs diet prevents gas. However,
> > I am sure that it began as green bean
> > don't cause gas as some other do. Anyway, she puts green beans into his
> > dinner bowl, which is OK since he
> > enjoys eating some "people food".
> >
> > 73
> > Bill wa4lav
> >
> >
> > From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on
> > behalf of Brian Clarke [brianclarke01 at optusnet.com.au]
> > Sent: Wednesday, October 30, 2013 1:47 AM
> > To: hwhall at compuserve.com; ARC-5 list
> > Subject: Re: [ARC5] dB Power Apples and dB Voltage Oranges,     was Re:
> > Selectivity Ratings...
> >
> > You may be referring to the work of Fletcher and Munson in the Bell labs
> > in about 1938. However, their work was based on laboratory experiments
> > with young listeners.
> >
> > We now know that the ear's ability to pick up slight differences depends
> > on, among other things:
> >   a.. age (presbycusis)
> >   b.. frequency
> >   c.. purity of the frequency (bandwidth, distortion within hearing
> >   range)
> >   d.. genetic differences
> >   e.. one ear or both
> >   f.. history of noise exposure (eg, working around tin bashing shops,
> >   repairing naval vessels, working on rocket motors)
> >   g.. history of hearing damage (eg, tinnitus)
> >   h.. disease of cochlear nerve and other parts of the hearing apparatus
> >   i.. duration at particular ambient noise levels
> >   j.. the 'reward' for hearing something.
> >
> > 1 dB is a purely mathematical definition and has nothing whatever to do
> > with human hearing acuity, consensual or otherwise. WRT your last
> > sentence, keep wondering.
> >
> > My own experience from working in sound recording studios is that a 2 dB
> > difference is about the limit that any reasonably experienced person can
> > reliably discern.
> >
> > 73 de Brian, VK2GCE.
> >
> > On Wednesday, October 30, 2013 12:25 PM, Wayne said:
> >
> >
> > > Good CW operators
> > > can hear as little as 1.5dB change and oft times even under 1 dB will
> bring
> > > a very marginal signal out of the noise.
> > >
> > > I seem to recall that the original 1 dB definition was based on a
> consensus of the smallest power change in an audio circuit that could be
> discerned by the human ear. I've always wondered how they conducted the
> tests to arrive at that, though.
> > >
> > > Wayne
> > > WB4OGM
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