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

Wed Oct 30 16:17:24 EDT 2013

Dennis
your comments seem to be dead on in my opinion.

In short in general it is not worth worrying about 1 dB however if you don't worry about 1 dB you will end up with something more like 2-3 db with is really worth worrying about.

Yeah i know the above sentence makes no sense logically but it does make sense practically. 

On Wednesday, October 30, 2013 4:12 PM, Dennis Monticelli <dennis.monticelli at gmail.com> wrote:

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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