From: WarmSpgs@aol.com
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Date: Mon, 7 Feb 2000 13:15:42 EST
Subject: Re: LF: Re: LF Propagation thoughts (and antenna, too)
To: rsgb_lf_group@blacksheep.org
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Rik writes:
> Regarding the groundresistance 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