Some random thoughts regarding “…long low metal structures of any kind do not make good VLF / ELF TX antennas, and for that reason are never employed. Also, they do not generate a vertically polarised signal, which is very necessary for VLF and ELF propagation.”
I also apologize for a narrow viewpoint, being interested in mainly in science, experimentation, practical applications and amateur radio, and in that narrow category long low metal structures have unique value for ELF, SLF, ULF, and VLF, and yield some exciting discoveries.
In practical applications at ELF, SLF, ULF, and VLF frequencies, long low metal structures provide underground magnetic fields for underground experiments, and high radiation angles for high-reliability low-power near field surface communications*
* (near field being 100km or more in part of that frequency range, and reliable thanks to the D layer)
The same is true for scientific, experimental and amateur radio applications:
In scientific and experimental applications at low frequencies, the high radiation angle of long/low metal structures is of exceptionally high value; it uniquely provides rich fundamental-physics information about ionospheric variations at short (hours, minutes) timescales.
In amateur radio low-frequency experiments, the high radiation angle of long/low metal structures has provided rare information of benefit to many RF communities, including:
2 kHz - 3kHz near-field propagation (an uncharted realm that computational modelling and analytical methods cannot yet effectively penetrate, but amateur radio finally did (during the past two years), with a long low metal structure, and shared the rare findings).
Examples from science, practical applications and experimentation:
a) Siple Station was a 24 mile long low metal structure (a wire), purposely made that way to give us otherwise-inaccessible fundamental information about the ionosphere (a vertical antenna would not have worked given its low radiation angle).
b) The geophysical exploration community uses long low metal structures for low-frequency work in part because they are interested in underground signals, but also because vertically polarized electric field signals, which would be of value to them, would be expensive to produce (construction costs), and their vertical antennas in many cases more damaging to the terrain (concrete supports for tall towers et al for vertical polarization, versus geophysical community’s ground loop antennas which have near zero environmental impact).
c) Amateur radio low frequency experiments using long low metal structures recently demonstrated an extraordinarily wide frequency range available from a portable low size/weight/power transmitter based on long low metal structures. The shared information form these experiments led to a thought from a bystander/reader of the shared information, that the long/low-structure amateur equipment developed for those low-frequency experiments might be used without modification as the D-layer bottom side ionosonde that has been sought for half a century (ionosonde candidate given its combination of exceptionally wide frequency range, high radiation angle and deployability). A practical D-layer bottomside ionosonde would be of value to many RF communities, and to physics communities and perhaps particularly to environmental science communities. I wonder if the device developed during those recent amateur experiments could be used as a D-layer bottomside ionosonde (any thoughts on this?).
Many apologies for the very long message; and for the narrow focus on high radiation angles.
Thanks for all prior comments in this thread, much interesting information from this discussion.
73,
Jim AA5BW
Hi David,
Several points of contention here – your description of Project sanguine is incorrect in some details (but you can blame Wikipedia for that). It was, in fact, rather like the antenna you so strongly object to. I would suggest you obtain a copy of ‘ELF Communications Antennas’ by Burrows. It is a bit dated now but is a good beginners text.
While VLF antennas tend towards vertical polarisation (I note you change from ELF to VLF here….) vertical polarisation is not a specific requirement for propagation but does make a rather more easily constructed (relatively compact) antenna for the frequencies concerned. I would also disagree with your description of the Beverage but why introduce it?
Discussion about whether or not to connect to infrastructure belonging to other entities is another matter entirely.
My background, by the way, is in antenna and comms system design for submarine systems so feel free to ignore me – I have a rather narrow viewpoint!
Regards,
Paul g8gja
Hi Neil, Then only published info that I'm aware of is the ELF antenna used by the USA to transmit ELF signals on 76 Hz to submarines. This was 'Project Sanguine'. It used about 15 miles of power cable suspended on 30 foot poles above ground and was earthed at each
end. A TX of around 5 Megawatts, about half way along this cable supplied the 76 Hz at a few hundred Amps. The radiated power was around 3 Watts, and was just sufficient to travel the globe. Project Sanguine was abandoned some years ago, as it fell obsolete as new sophisticated comms replaced it, such as satellites etc.. It was very expensive, only one way comms, and the 15 mile of cable was constantly being attacked by vandals and metal thieves. Russia still uses a similar system on 82 Hz (Zevs), and they shoot to kill anyone tampering with their cable!!!
There is an excellent Wikipedia page on Project Sanguine. Basically, it was a very inefficient monster narrow loop.
Otherwise, conventional Marconi vertical masts tuned against ground are used for VLF TX'ing the vertically polarised signals, at any
VLF frequency up to the LW broadcasting band.
From my experience, long low metal structures of any kind do not make good VLF / ELF TX antennas, and for that reason are never employed.
Also, they do not generate a vertically polarised signal, which is very necessary for VLF and ELF propagation. The historic 'Beverage' type of horizontal wire antenna is long, but only suitable for reception (very inefficient as a TX antenna).
Vertical balloon suspended wires do work, but you must observe the maximum height restrictions allowed in any particular location.
This sounds interesting. Can you point at any published results to explain what technique was used, what power was used to obtain those results, and how the signal was launched? I imagine lots of people are considering the use of long lengths of metal infrastructure (on private land, with the express permission of the landowner), so if there is a solution which is demonstrably better, it would save a lot of unnecessary trouble for experimenters.
Do you have any numbers comparing the technique used in these experiments against those obtained from using long lengths of armco or metal fencing or huge bridges, (putting aside any arguments about the rights and wrongs). It would be good to see a documented comparison to show by what margin the experimental technique used is superior to using low steel structures with a large horizontal extent.
On 10/01/2019 18:37, David Hine wrote:
... TX connexions to motorway
guard rails, railway infrastructure, electric / gas supply utilities and fences etc. are totally unnecessary for the transmitting of ELF
These DO NOT make good VLF / ELF TX antennas ..
