Posts Tagged ‘VLF’
How Low Can They Go!
May 16th, 2019 | 
Author:  |
| courtesy: Roger, G3XBM |
For the past few years several amateurs in Europe and along the east coast of North America have been experimenting on the ‘dreamers band’, 8.7 - 9.1 kHz.
Some rather surprising distances have been covered on these frequencies in spite of the dreadfully poor efficiencies realized with backyard antenna systems.
Previous 'earth-mode' backyard experiments on VLF by Roger, G3XBM, are well documented on his website along with details on his simple homebrew gear used to send signals across town using the earth. Following Roger's steady progression via his previous blog spots makes for fascinating reading ... there is some really great stuff here making it difficult to not jump in and take the plunge yourself.
This experimental field presents the ideal opportunity for a couple (or several) local amateurs to work together at exchanging signals on these low frequencies with simple home built equipment.
A major contributor to the present state of the ‘VLF / ULF amateur art’ is Stefan, DK7FC and a posting this week to the old RSGB's (blacksheep) LF reflector makes some of his earlier work pale by comparison as he announced the reception of his 270Hz signal (the 1110km band!) at a distance of 177 km!
Just a note from a recent experiment at 270.1 Hz.
On Sunday morning, 2019-05-12_10:34,+150m, I've done a carrier transmission on my ground loop antenna again. I did not expect more than, hopefully, a detectable spectrum peak in 57.6 km distance, i.e. at my tree site. The tree receiver site was listening and recording data using vlf-rx tools.
One E field antenna and two orthogonal loops were listening. The loops have been improved recently! They consist out of a single circular turn of 1.2 m diameter using 10mm diameter copper tube (about 25 mm^2). It is a closed loop, non-resonated, with an impedance matching transformer. This transformer previously had 1:100 turns. Now it (they) has 2:240 turns, i.e. two turns primary (out of 14mm^2, AWG6). This improved the sensitivity below 2 kHz significantly ( abt. 4...5 dB).
Furthermore the TX antenna length and angle has been improved, resulting in about +3 dB more signal strength on the RX site!
In a previous experiment at 270.1 Hz, some month ago, there was no result at all, not the weakest trace, despite excessive tweaking of all parameters. So the question was, will the improvements result in a detectable signal now?
Several things went wrong in that experiment. I forgot a bag containing important equipment such as the power supply for the netbook that generates the carrier signal. Also the output power was not as high as planned, just about 380 W, giving 2.2 A antenna current (I measured 64.7 V at 1 A DC). Anyway i managed to improvise so the experiment was started, but with some hours of delay which meant i higher QRN background level. Then, on the WLAN link to the tree, there were several interruptions of the stream (i'll move to 5 GHz very soon!). I even got some QRM from my battery charger for some short time periods (forgot to disable the charger remotely). So there were several factors that could have been improved or avoided. And the middle of May is not the ideal time anyway.
Well, 270.1 Hz, that's the 1110 km band! The far field begins at 177 km distance, i.e. i am clearly in the near field here. Thus, from a 'magnetic' TX antenna, we would expect that the signal is mainly detectable on the H field, i.e. the loop antennas.
The first interesting results is that this expectation is actually confirmed. There is nothing detectable on the E field but the carrier S/N in the H fields is close to 10 dB in the first run. Mixing the H fields and tweaking the filters rises the carrier S/N to 10.7 dB, see attachment.
So far not really an undoubtedly detection but it is a candidate for optimism! With a few less problems during the experiment there is a chance for 14 dB SNR. Also, there is quite much sideband QRM around 300 Hz which makes 270 Hz a bit harder to work on.
73, Stefan
The G3XBM Experimental Blogs
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| G3XBM's 5W Earth-Mode Tx (courtesy: G3XBM) |
My interest of late has been piqued by the ongoing VLF experimental work by several European amateurs.
Recalling that Roger, G3XBM, did some VLF experimenting a few years ago, I have been reviewing some of the excellent hands-on information gathered and published in his ham radio blog and to some of his other VLF pages.
It's not the first time that I have found project-inspiring reading within Roger's blogs. They really are a treasure-trove of useful information, construction notes and accumulated test data gathered from his methodical approach to so many interesting topics ... experimental amateur radio at its very best.
A few years ago I was immediately hooked by his experimental lightwave work, both line-of-sight and clear-air / cloudbounce scatter ... so much so that I also became involved in some lightwave work with other locals who were also inspired by Roger's information, culminating in our own West Coast Lightwave Adventure.
Roger's VLF experiments are also proving hard to resist, especially those of the earth-mode type and I may find myself falling victim to his detailed Sub 9kHz Amateur Radio pages and the Earth Mode pages in particular.
It seems that most amateur VLF work is being done in the vicinity of 8kHz since this part of the frequency spectrum is unassigned. I gather that one can conduct earth-mode tests in any portion of the VLF spectrum since no signal is being 'radiated' as is typically done via antennas. Further investigation remains to see if I need a 'developmental licence' to conduct some radiated (non-earth-mode) experiments in the 8kHz range as well.
Getting a VLF signal from here on Mayne Island across Georgia Strait via earth-mode or via conventional methods would make an interesting challenge and would certainly result in some new homebrewing opportunities.
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| courtesy: https://www.google.ca/maps |
Here on the island, I often hear audio associated with the container terminal and ship-loading operations near Tsawwassen, directly across the strait from here. I feel that this may be aided somewhat by the solid sandstone of the island being directly connected to the other side, so perhaps an earth-mode system utilizing the ocean as one-leg of a buried loop might be an interesting experiment to tackle ... or groundwave transmissions across the ocean via an antenna, to the other side, providing I could find someone to listen.
I see just two Canadian amateurs experimenting on VLF ... VO1NA (Joe) and VA3VVV (John) near Toronto. Any VE3's in the area who are interested in VLF may wish to contact John and exchange notes. He has a Facebook page showing his VLF setup. Interestingly, Joe's 30W VLF signal on 8.270 kHz has just crossed the Atlantic! Joe is documenting his VLF experiments here.
All of G3XBM's VLF blogs can be downloaded for reading or for printing via this link. Similarly, his lightwave experiments can all be found here ... both links will yield several pages of material if you click on the 'Older Posts' link at the bottom of each page.
The best way to follow these is chronologically which requires going all the way to the end of the final 'OlderPost' link and follow along with Roger as he gradually develops, evaluates and improves the gear that he needs to make progress. This is fascinating reading.
But be suitably warned ... you may readily fall victim to his experimental work as well and suddenly find yourself with another exciting project!
The G3XBM Experimental Blogs
|
| G3XBM's 5W Earth-Mode Tx (courtesy: G3XBM) |
My interest of late has been piqued by the ongoing VLF experimental work by several European amateurs.
Recalling that Roger, G3XBM, did some VLF experimenting a few years ago, I have been reviewing some of the excellent hands-on information gathered and published in his ham radio blog and to some of his other VLF pages.
It's not the first time that I have found project-inspiring reading within Roger's blogs. They really are a treasure-trove of useful information, construction notes and accumulated test data gathered from his methodical approach to so many interesting topics ... experimental amateur radio at its very best.
A few years ago I was immediately hooked by his experimental lightwave work, both line-of-sight and clear-air / cloudbounce scatter ... so much so that I also became involved in some lightwave work with other locals who were also inspired by Roger's information, culminating in our own West Coast Lightwave Adventure.
Roger's VLF experiments are also proving hard to resist, especially those of the earth-mode type and I may find myself falling victim to his detailed Sub 9kHz Amateur Radio pages and the Earth Mode pages in particular.
It seems that most amateur VLF work is being done in the vicinity of 8kHz since this part of the frequency spectrum is unassigned. I gather that one can conduct earth-mode tests in any portion of the VLF spectrum since no signal is being 'radiated' as is typically done via antennas. Further investigation remains to see if I need a 'developmental licence' to conduct some radiated (non-earth-mode) experiments in the 8kHz range as well.
Getting a VLF signal from here on Mayne Island across Georgia Strait via earth-mode or via conventional methods would make an interesting challenge and would certainly result in some new homebrewing opportunities.
|
| courtesy: https://www.google.ca/maps |
Here on the island, I often hear audio associated with the container terminal and ship-loading operations near Tsawwassen, directly across the strait from here. I feel that this may be aided somewhat by the solid sandstone of the island being directly connected to the other side, so perhaps an earth-mode system utilizing the ocean as one-leg of a buried loop might be an interesting experiment to tackle ... or groundwave transmissions across the ocean via an antenna, to the other side, providing I could find someone to listen.
I see just two Canadian amateurs experimenting on VLF ... VO1NA (Joe) and VA3VVV (John) near Toronto. Any VE3's in the area who are interested in VLF may wish to contact John and exchange notes. He has a Facebook page showing his VLF setup. Interestingly, Joe's 30W VLF signal on 8.270 kHz has just crossed the Atlantic! Joe is documenting his VLF experiments here.
All of G3XBM's VLF blogs can be downloaded for reading or for printing via this link. Similarly, his lightwave experiments can all be found here ... both links will yield several pages of material if you click on the 'Older Posts' link at the bottom of each page.
The best way to follow these is chronologically which requires going all the way to the end of the final 'OlderPost' link and follow along with Roger as he gradually develops, evaluates and improves the gear that he needs to make progress. This is fascinating reading.
But be suitably warned ... you may readily fall victim to his experimental work as well and suddenly find yourself with another exciting project!
Amateur radio below 9kHz
Until a few years ago, the conventional wisdom was that you needed huge power and huge antennas to be copied “beyond the garden fence” at VLF and ULF. In recent years much has changed and time and again great distances have been covered by amateurs with quite low power and modest antennas.
The trick is great stability, very narrow bandwidths and long integration times, often of days. For several years just detecting a carrier was enough, but in recent times people have been sending simple messages using EbNaut software.
When at the old QTH I detected signals from several European countries using simple, homemade gear and free software.
Although not totally up to date at all times, I try to update news of amateur VLF and ULF experiments at https://sites.google.com/site/sub9khz/ .
Hearing The Hum?
An interesting item in Global News today caught my attention. In 2012, Glenn MacPherson, a teacher living in Gibsons, BC (a coastal community about 50 miles north of me and line-of-sight) began to hear a low level 'hum'. At first he thought it might be coming from local float plane activity but soon ruled that out. After Googling for any information about possible causes, he quickly learned that he was not the only one hearing ' the Hum' ... so he set up a website where people could report what they were hearing and found that it was a worldwide phenomenon. Possible theories for what has been described as 'hum' and 'rumbling' range from VLF transmissions to submarines to “ 'nothing more than the grand accumulation of human activity' that could include noise from highways, marine traffic, mining, windmill farms, hydroelectric dams and other forms of industry."
MacPherson speculates that some people may indeed be sensitive to VLF frequencies.
“When I say VLF, I’m not referring to sound,” MacPherson said. “That leads to another striking and startling conclusion, the fact that the Hum may not be a sound in the traditional sense. It may be the body’s reaction to a particular band of radio frequencies. That’s not an outrageous idea. The concept that the body can interpret certain electromagnetic frequencies as sound is reasonably well-established in research literature.”
MacPherson has now built a large Faraday cage to follow up with his VLF theory.
So far, over 9000 reports of the mysterious Hum have been filed on MacPherson's website's database and plans to translate the site into Chinese will likely see that number soon rising.
Here on Mayne Island, it is very quiet and stepping outside on a winter night when there is no wind or no waves hitting the beach there is truly not a single thing to be heard, including the Hum. I do however, on warm summer evenings, often hear the rumblings coming from the Roberts Bank coal loading facility and container port, on the other side of Georgia Strait about 12 miles away.
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| Roberts Bank courtesy: http://www.vancouversun.com |
Perhaps you can hear the Hum as well and might like to report it or discuss possible sources with others.
Amateur VLF DXing
Operating an amateur station at VLF is a very specialised area of experimentation. There are basically 2 different threads (1) earth-mode or utilities assisted earth-mode with propagation mainly along or close to roads and (2) radiated DXing in which a VLF signal is actually radiated and propagated to great distances. With (1) I have managed 6km with QRSS3 with 5W from a TDA2003 audio IC at 8.97kHz. Earth-mode gear can be low powered and simple to build.
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| VLF amateur signals |
With (2) the Atlantic Ocean has now been crossed, i.e. quite remarkable distances with amateur powers and antennas. Usually very large loading coils are needed and making these can be “challenging”. As high voltages are likely, great care is needed. Of course, most DXing is done with very long stable transmissions in very narrow bandwidths. Most amateur VLF gear is home made with free PC software to allow signals to be seen. Casual listening is not effective. Most operation is now around 8.300kHz as this is unallocated in many countries.
News of VLF activity may be found at https://sites.google.com/site/sub9khz/ .
VLF field test – a total failure!
Well, I did my first VLF earth-mode field test today since my brain bleed in Sept 2013. Sadly, it was a total failure. I am at a loss to explain the results.
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| Tuned VLF loop |
I put the 5W, 8.976kHz, beacon on into the same earth electrodes used successfully on 472kHz (best DX on TX over 1000km) and went about 1.6km to a car park where I always had strong signals using a tuned loop on RX and earth-electrodes on TX from the old QTH in the same village. Nothing at all copied today – absolutely nothing. I waited in case I was in a pause between QRSS3 callsign transmissions, but no absolutely nothing at all. Not even the tiniest hint of a signal.
So I parked in the road about 0.3km from this QTH and again nothing at all. At this point we drove home.
Sure enough, everything was still working at the TX end. I am using one remote ground and the mains ground as the shack end as for 472kHz. I did check this was grounded to real ground.
So, whatever utilities assistance I was getting before at the old QTH is not the same at this newer QTH. All very very odd. I was expecting to see something. In the past I received transmissions from the old QTH at the new QTH (about 0.3km away) using just an E-field probe on the car. From the old QTH I spanned 6km!
In summary, this VLF test was a total failure. I am at loss to explain things. Not only that, but the work has left me very exhausted. My brain is still foggy, but the results today were not due to any mistakes with the HW gear or PC Spectran settings.
I am not having much success today.
