[TowerTalk] Fw: Feeding single band HF yagis 500+ ft from the shack

[Grant Saviers]

I think in difficult SSB conditions, high noise, fading, QRM, many 
repeats and Q's at the margin, 1db can make a difference.  Our brains do 
the rest.  My friends that swear by diversity reception for CW on 
dxpeditions also are copying signals with a few db differences.  Our 
brain's being inside the decode "system" makes quantitative analysis 
pretty difficult.

I also look at this topic from a cost/benefit perspective.  $3000 
differential amplifier cost from 700w to a real 1500w.  That's 3db or 
$1000/db.  $1000 buys a lot of low loss coax.  It's easy to build a 
spread sheet of all loss from amp output to antenna feedpoint.  My goal 
was 1db or less and it was achieved band by band deciding if LDF5, LDF4, 
or Buryflex would achieve the goal. Other contesters also set their goal 
at <1db loss.

As was also noted $25k for a tower and yagi to gain 6db over a dipole 
and $200 for coax to subtract 2db isn't good engineering.

Contesters that stack 2 to 4 yagis think that a couple of db's are worth 
$$$$.

"pretty soon a fraction of a db here and there adds to 3db"

Grant KZ1W


On 5/18/2022 09:38, john at kk9a.com wrote:
> I do not know of any such study but I agree with K9YC that every bit
> matters.  Certainly at some point having an extra 1dB of gain or 1dB less
> loss becomes very expensive so everyone has to weigh how important it is to
> them.  I'm sure that K3LR minimizes every fraction of a decibel of loss at
> his station.
> 
> John KK9A - W4AAA
> 
> 
> Kim Elmore N5OP
> 
> I don't mistrust contesters that tell me they're certain of this, but...
> I'm wondering how they *know* that the difference is 1-2 dB on the
> *receiving* end? If they can increase the smoke by 1-2 dB and all of a
> sudden make the QSO, how do they *know* that's what did it? HF
> propagation is funny stuff. I do a LOT of statistics in my job as a
> research meteorologist/scientist, even though I'm not a formally trained
> statistician, and this is always my first question when presented with
> statements like this. Show me the data and how it was analyzed.
> 
> I'm pretty sure that there is no such data set in existence and I don't
> know of a good way to collect one. However, I suspect that the innate
> variability of ionospherically propagated HF signal strength is far
> larger than 1-2 dB and that any p-values we'd find at the 1-2 dB
> thresholds would be pretty large and so deemed statistically
> insignificant. I suspect there are too many degrees of freedom to ever
> pin this down.
> 
> I have no intention of starting a fight or creating discord. I *deeply*
> respect Jim's judgement and experience. Even so, I'd love to craft an
> experiment that would allow us to statistically determine the dB
> threshold that truly makes a difference on each band. While I'm
> spitballing, I might as well include different geomagnetic conditions as
> well.
> 
> That said, there's also a good argument for not wasting a dB if you can
> affordably avoid it.
> 
> 73,
> 
> Kim N5OP.
> 
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