[AMPS] Re: SSB Power Output

[John Nelson]

Message text written by T A RUSSELL

>Are you suggesting that a few dB of antenna gain differential is more
significant than 10 dB of power differential?   N4KG<

No. Other things being equal, of course I'm not suggesting that the 10dB
amplifier will be more significant than a few dB of antenna gain. I'm
suggesting that antenna siting factors will tend to have much more effect
on the real-world performance of the station averaged over time -- and that
other things are generally far from equal. 

It seems fairly well established in the professional as well as the amateur
literature that antenna height, siting, local soil conductivity and
roughness, local obstructions, height above average terrain and similar
factors -- as well as gain and pattern -- will have a more profound effect
on the day-to-day performance of an HF station than the absolute value of
transmitter power. For example, suppose your antenna is on a tower sited on
the side of a hill several hundred feet above sea level, with a clear slope
down to a river valley a mile or two away. Or suppose you live on a coastal
site with a slightly elevated location looking over the sea. It's likely
that in either case, a given HF band will open earlier and close later (at
least in the "good" directions) than it will for someone living inland on a
flat site with a lot of local obstructions. On many paths it's also likely
that there will be several S-points difference between the signals, even if
transmitter power and antenna gain are the same in both cases. No amount of
ERP will open a band that's not quite open at your particular location. 

During my time with the BBC, one particular HF site was well known over the
years to be a lot less good on both long-haul and short-haul paths than two
others even though all three used similar transmitter powers and antenna
systems. A lot of work (including some very clever computer modelling by
the standards of the early 1980s) was done to find out why this was the
case. The most significant factors were found to be pretty much the ones
mentioned above, and nothing could be done about them short of moving the
site wholesale. In the end we closed the entire station!   

>Actually,  Dr. Laura vehemently denies that her program is a "psychology
show".   She prefers her show to be considered as a "morals and philosophy"
program. I was not aware that it aired outside the USA.  :-) <

I've never seen the show, or indeed had never even heard of it until today.
The nearest we get is probably Oprah Winfrey <g>. 


John Nelson
GW4FRX


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