[Lf] LF Propagation thoughts (and antenna, too)]

[Andre' Kesteloot]

WarmSpgs at aol.com wrote:

> Rik writes:
> > Regarding the ground resistance the rules was : the lesser the better. No
> > only for the sake of antenna effeciency but also to avoid radiation at
> > higher angles. This 'high angle radiation' was for the commercials, who
> > were only interested in surface wave propagation (stable 24h/day, 365
> > days/year) not only pure waste but also a source of possible interference
> > (via ionospheric wave).
> >
> > But if we want to make 'DX-QSOs' with 1 Watt ERP we defenitely need
> > ionospheric wave propagation, so producing some higher angle radiation
> > might be usefull.
>
> Yes and no.  Commercial and military LF stations do not depend on surface
> wave alone, especially not at transatlantic distances.  One cannot achieve
> globe-spanning distances with surface waves above roughly 100 kHz; and even
> some ways down below 50 or 60 kHz, conventional ionospheric refraction still
> plays a significant role.  It is not until one gets down to VLF that the
> propagation model changes dramatically.
>
> The commercial guys do suppress high angle radiation to whatever extent
> possible, but that's not because they are only interested in groundwave.
> High angle radiation causes problems with the more desirable low angle
> skywave at intermediate distances, and wastes power that would be more
> beneficial for long-distance coverage if it could be radiated at the lower
> angles.
>
> If one were able to radiate most of one's power at, say, less than 5 degrees
> above the horizon, the signal would stand a far better chance of making it
> across the ocean than if the bulk of the power were 20 or 30 degrees above.
> That's where the region of the ionosphere is that we want to excite.  (I keep
> saying "if," though, because in practice, any short vertical already has
> plenty of high angle radiation well above 30 degrees, whether we want it or
> not.)
>
> Further increasing high angle radiation with horizontal runs of wire may have
> interesting propagation effects, as described in another post, but this is
> over medium distances.  We must take into account how much "D" we are really
> talking about when we speak of transatlantic DX.
>
> I'm not speaking of this from a theoretical standpoint so far as amateur
> efforts are concerned, either.  Nor do I mean, in what follows, to detract
> *in any way* from the excellent work being done by the AMRAD group.  They
> have opportunities to experiment with power levels and antenna lengths that
> we 1 watt / 15 m antenna LowFERs can only dream of for now, and I have no
> doubt that much valuable information will result.
>
> I merely point out that the recent successful copy of the AMRAD beacon in
> Ontario, despite the long horizontal antenna and the power levels involved,
> does not quite yet match some of the DX achieved by stations working within
> the 1 w / 15 m limits.
>
> Utilizing much patience and only moderately slow digital techniques, one-way
> copy has been achieved from California to Minnesota, Georgia to Minnesota,
> Texas to Quebec, and more.  (I nearly hesitate to mention the old CW LowFER
> record from California to Hawaii, as it required a once-in-a-lifetime
> combination of good propagation, ideally situated stations, and remarkably
> low noise levels.  Yet, there it was.)  Apart from the latter example, the
> stations were sending Coherent CW or BPSK.  All, without exception, employed
> vertical antennas, top loaded to the maximum extent allow by regulations,
> working over the best ground systems that their operators were able to
> achieve!
>
> At no time would I suggest that anyone is wasting their time pursuing new
> ideas.  However, I don't think it would be productive to arbitrarily set
> aside the commercial operators' examples as being irrelevant, either.
> Especially, in the face of such strong experimental evidence that what's
> sauce for the commercial goose may also be sauce for the amateur gander.
>
> 73,
> John  KD4IDY