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Hello gang,
Since our professional
controversialist ('3KEV)
This is known as individualism and not following the
mob. Some people are individuals and express their opinions. Some have the
sheep mentality and some are brain washed by the establishment. Dont rock
the boat even you know they are wrong. Keep your antenna buried during
daylight and only bring it out after dark in case you upset your neighbour.
Take your pick.
has
raised the big/small antenna discussion again, and I'm fed up playing
Scrabble, here's a few points he might like to ponder on while he's drinking
in the New Year:
The "professional" antenna/system
engineer's job is to provide a guaranteed signal at all times 24hrs/day, 365
days a year. If it is a navigational system, as we had in Decca, not just
guaranteed field strength but guaranteed phase stability as well, to better
than 10 degs. You can't do that with a piece of wire waving in the
wind; coils of unknown and variable characteristics, poor earth systems,
etc. And you want to minimise skywave as much as possible; it's just a
nuisance. So you go for a vertical, the bigger the better, not particularly
because it radiates better but because the bigger it is the more predictable
and stable it is. You want absolutely stable characteristics whether
it's wet, loaded with ice, covered in snow, or blowing a Force 12
gale. And you don't want to pay for a team of skilled engineers to be
permanently on site 24 hrs/day to re-tune it every time something
changes. Automatic tuning can do a bit for you but not everything.
Then there's cost. A big antenna costs a lot in initial purchase and
annual maintenance, sure, but not as much as installing a 2 megawatt
transmitter and paying for its maintenance and the electricity it
consumes. Some high-powered Russian navigation transmitters have gone
off the air recently because they couldn't afford the electricity
bill. You have to look at where your income is coming from and
whether it will support the running costs of the high-powered transmitter
you're going to have to put in because you're only going to have a little
aerial. Years ago I used to have to do this sort of calculation and
believe you me the big antenna is cheaper and a good deal less trouble in
the long run.
This is apart from the sheer engineering consideration
of how much field strength you need and where. The BBC consider that at LF
they need a minimum of 1 millivolt/metre to get a signal into a little
tranny in a block of flats in a city. This is about S9+60 db by
amateur standards (please, no arguments about what amateur S-points mean!)
and results in things like the 400 kW e.r.p Droitwich transmitter to serve
only a 200-mile radius but which can be heard in America quite often.
Note, incidentally, that as pointed out by others, range depends ONLY on
e.r.p. in the direction you want, it doesn't matter how you produce it. And
yes, if it was possible to get 1W radiated out of a 10 foot vertical antenna
at 136 kHz it would work just as well as 1W out of a 600 ft vertical. At 136
kHz all antennas are tiny and radiate omni-directionally in the vertical
plane. The differences would be you would need something like a 25 kW
transmitter instead of a 2.5W tiddler; as soon as it got foggy everything
would arc over; it would be impossible to keep loaded efficiently even
if you sat with one hand on a tuning control, you would have to spend a lot
of money on very good insulators, (and go out and polish them every few
hours), etc, etc. In other words, totally impracticable if you want
24hr availability. And yes, I have tried it, about 30 years ago
we tried to radiate a 100 kHz signal off a 10 ft stick (coil, actually) ; in
perfectly dry conditions (Arizona desert) it (sort of) worked, but it
never worked in England for more than a few minutes. Theory 10, practicality
0. As a matter of interest we eventually made the system work reliably
around the North Sea by using 180 footers (it was a variety of Loran-C in
case anyone's interested - closed down some years ago in favour of DGPS).
As amateurs we might well decide it's worth living with a lot of
this aggro just to get those few minutes across the Atlantic, but
professionally you can forget it. So please stop making silly comparisons
between amateur and professional practice. Quite a lot of us
"amateurs" are also "professionals" but find
"amateur" work liberating after the irritating constraints of a
lot of "professional" work.
My goodness, this bottle of
"Glenfiddich" has gone down rather quickly - and it's not even the
New Year yet!
Happy New Year, Gluckliches Neues Jahr (sorry I don't
know any Dutch, Swedish or Finnish!)
Walter G3JKV.
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