[TowerTalk] 1 or 2 dB

[Kim Elmore]

My test worked, so I'll try again...

To everyone that has commented: Thank you very much! This discussion is 
fabulous!

I concede the point that statistically, there is likely to be score 
improvements with 1 dB power increase and certainly 2 dB. These are best 
described as statistical improvements and I suspect that the data set 
has to be moderately large to detect a "significant" difference, that is 
for a statistic to have much power. Thus a DXer, who is not a contester 
(there are such things) probably won't notice a significant improvement 
in how long it takes to break through a pile-up with a power increase of 
1 dB. Over a long run, a contester will be able to see a score increase 
at with a 1 dB power increase.  A smaller data set (possibly much 
smaller) will show statistical score improvements given a 2 dB increase, 
significant at some arbitrary p-value.

I tend to skepticism when someone says they can notice a significant 
improvement given a *single* contest assuming everything else (including 
the operator) is held constant. It will take several contests to see a 
*statistical* improvement but I'll now bet it's there. Fewer contests 
will be required for a 2 dB increase. I prefer resampling (i.e. a 
permutation test) to parametric statistics simply because parametric 
test assumptions are almost always violated, leading to unknown 
degradations of the test's validity.

Dave's response is precisely what I would expect to see. I became aware 
of diversity reception early in my ham radio experiences and that it 
could lead to huge effective signal increases (10 - 20 dB) but it's not 
trivial for a typical ham installation. I heard about it as it related 
to multiplexed encrypted RTTY military applications.

I've always assumed that propagation was king: without favorable 
propagation, we're sunk. I re-read the section on fading in Ken Davies's 
book "Ionospheric Radio"  (I knew him when I worked in Boulder and he 
gave me an autographed copy) about the mechanisms of fading -- I don't 
recall Jim Lux's notes about ionospheric "lumpiness," but it makes 
*perfect* sense, and it's right there in black and white in Davies's 
book as well. .

A personal historical note: when my dad (W5JHJ) worked in as an 
engineering physicist, he developed an instrument to fly on the KH-8 
surveillance satellites that would help us determine the vehicle's 
orientation. The KH-8 orbited pretty low (80-200 mi) and so was in the 
ionosphere. Of course, I was only a kid (elementary school) at the time, 
what he did was Classified, and he only told me the whole story when he 
was long-since retired and the program was mostly declassified. His 
instrument used the acronym "AIM" (I never knew what that acronym stood 
for) and was later called a VVSA -- velocity vector sensor assembly. It 
measured ion current through two perpendicular ports and, based on the 
difference of the currents, determined the direction of the "wind." At 
the time, it was a challenge to know exactly how it was oriented, so the 
idea was to sense the ionospheric "wind." The AIM did that quite well 
but they found strange anomalies indicating that in places the 
ionosphere had very high velocity winds, on the order of the orbital 
speed of the KH-8, which rendered the AIM useless for its intended 
purpose. They had f made unintentional direct measurements of 
ionospheric winds; this was all sometime in the 1960s. These currents 
were hypothesized by Kristian Birkeland and then detected by him based 
on magnetic anomalies, all in the early 20th century. Of course, none of 
what my dad was part of was ever published because it was all 
classified. By the time that veil had lifted, we had radar measurements 
of the these currents and so what my dad was inadvertently part of 
finding was never written up for any publication.

Kim N5OP

On 5/18/2022 7:53 PM, Dave Sublette wrote:
> I've hesitated to chime in here because I thought the problem was being
> discussed very well and perhaps I don't have anything to add.  But I do.
>
> >From December 1983 to April 1989 I operated 160 through 6 meters from
> Kwajalein, Marshall Islands.  The pileups were big and were there every
> time I pressed a key or opened a mic.  I made 83,000 QSOs, filled 19
> logbooks. There were no home computers for me at that time.
>
> One night things were a bit slow on the bands and I had three stations in
> San Diego on 20 meters to keep me company.  All were running comparable
> stations.  KW and tribanders at 70 feet.  They all lived within a couple of
> miles of each other.  So I proposed an experiment.  I had them each say a
> sentence in turn, perhaps no more than 6 seconds.  And keep it going
> around, one sentence after another.  I watched my S-meter.  At any
> given moment, one of them would be 10 to 20 dB stronger than the other
> two.  And it was a different station each time.  We did this for maybe ten
> minutes and the results were as I have described.
>
> I learned some things from this that I wish I had known while chasing DX
> from the States before I went to Kwaj.  Primarily, propagation is king.  No
> amount of power will guarantee your signal to be highest at all times.  I
> came to think of propagation as a searchlight, constantly scanning.
> Whichever station is shined on at the moment would be the one that got
> through the pileup. Had I realized this, my anxiety level about working the
> DX over the years would have been much lower. Sooner or later, it will be
> your turn.
>
> The second thing that occurred to me is that there is no substitute for
> crisp operating technique.  Call only when the DX is listening. Hear the DX
> station before you call.
>
> In any pileup I could hear at least five levels of signals, even when
> everyone one was transmitting at the same time.
>
> Based on all of the above, I would tend to disregard any worry over one or
> to dB.
>
> But, as was pointed out, over the long haul in a contest it evidently makes
> a difference.
>
> There are two other circumstances where 1 or 2 dB makes a difference.  EME
> communications.  We don't strive for that last tenth of a dB noise figure
> for no good reason.
>
> The other circumstance in my mind would be digital modes on a "dead" band.
> It could make a difference of whether or not the report was decoded.
>
> Just my two cents worth.  I have enjoyed the discussion.
>
> 73,
>
> Dave, K4TO
/
/