Regarding earth probe antennas, there is a Facebook page dedicated to them at <https://www.facebook.com/groups/earthprobes/>.?
Another link on the page at <https://www.rtl-sdr.com/building-an-underground-earth-probe-antenna-for-0-14-mhz-tx-rx/> references a 1935 article about a buried antenna for SWL.
A search for "buried antenna" gives numerous links and eventually I found links for Soviet and US military documents related to underground antennas used in Cold War communications systems.
I'm more inclined to the simple "LOG- Loop On Ground" concept.
73, Doug Reed, N0NAS.
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Further attempt to improve my LZ1AQ installation
I tried to follow recommendation from Chavdar's app note in regards to feed cable location (for vertical dual loop configuration). Here is a picture:
?
?
Although in the notes Chavdar recommends 1-2m offset for the cable behind the loop's plane. I only have ~60-70cm (2ft) due to some space restrictions.
?
I noticed that in Dipole mode I see about 5dB drop in AM BC station images in the lower 80m band. That's due to CM issues in dipole mode. Not sure if that was worth the hassle as loop mode is still superior in my noisy environment (semi-urban location).
?
I also noticed that top loop (Loop A) usually provides better s/n ratio compared to lower loop (loop B) and cross-parallel connection of both loops. I see that on most HF bands. Sometimes LoopA=A+B but usually I just use loopA. I was wondering if that's due to the cable that was hanging right across the lower loop. New cable placement improved things a bit but I still see LoopA normally being better or equal to A+B configuration. LoopB is still normally worse than other two configs (A, or A+B).
Next I may try to put more clip on ferrites along the portion of the cable that hangs below LoopB. Maybe mix31 and mix75 clip-ons combined on the length of 1-3m up to the point where cable comes to the wall. I already have a stack of two FT240-31 with ~6 turns of CAT before cable leaves the amplifier box and a stack of three FT240-31 with 6 turns before it enters control switch box. That actually helped a lot but I wanted to improve things even more.
?
I wonder if Loop A is better simply because it's higher in the air and further away from my "shack" that's 2-3m away from the antenna physically.
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Also may try to place Yaesu GS-050 mast bearing a bit lower. Right now it sits right below the lower loop. Wonder if that can create any un-balance issues.
?
Regards,
Simon
KM6MUL
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Re: File upload: Rotable FLAG-antenna
Hi Fred, Thanks! I wonder what difference will UTP vs S/FTP make? I use S/FTP cat8 (24awg) patch cable for my LZ1AQ (original AAA-1). I know that at antenna side cable shield is not connected to common GND to keep line symmetrical (relative to GND) and for less CM issues. Same should be applied for other antennas if shielded CAT is used (shield not connected on one side, most likely antenna side)... Regards, Simon On Tue, Feb 11, 2025 at 9:57?PM Fred M via groups.io <dl4zao@...> wrote:
On Tue, Feb 11, 2025 at 04:17 PM, Warren Dean / NI5L wrote:
Would there be any problem feeding the antenna and pre-amp with CAT-6 cable?
No, there would be no problem, this a a proven technique. Te original LZ1AQ AAA-1C active loop is using twisted pair Ethernet cable as feedline, power supply line and control line..
"Ethernet cables are designed to handle frequencies that coincide nicely with most of the interesting amateur radio bands, and their insertion losses not much worse than RG58. The twisted pairs are also a balanced system that’s good at rejecting common mode noise. Cat 6 cable also has four pairs of conductors, allowing you to feed multiple antennas with one cable, or to distribute power to amplifiers and switches along with antenna feeds."
Video:
regards, Fred
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A mate of mine also builds DSP-based cave radios ,operating at around 87kHz, which is a coomnly used frequency for such purposes.
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The antennas are tuned loops
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Regards,
?
Martin
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On Wed, Feb 12, 2025 at 12:01 PM, Fred Moore wrote:
Martin, great history document
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Re: File upload: Rotable FLAG-antenna
Thanks for that, Fred. I am definitely going to use CAT6 for the loop. We shall see how it works out.
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73
Warren / NI5L
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Martin, great history document. Who would have thought that buried wire could actually have worked that well. Thanks for the history lesson. Fred N4cla On Wed, Feb 12, 2025, 06:17 Martin - Southwest UK via <martin_ehrenfried= yahoo.com@groups.io> wrote:
I think the issues is how much contribution there is from the ground path vs, the interconnecting wire laid on the surface.
?
Earth probes and amplifiers were extensively used during trench warfare in WWI, in order to eavesdrop on field telephones, that at the time used the earth as a return path for the single wire phone line. Twin wire was then introduced, and latterly the Fullerphone, with increasing development to further improve security.
?
?
The earth itself is a lossy dielectric medium, but at VLF it's mainly resistive, the ground conductivity, and underlying geology having a major effect on propagation.
?
50 or 60Hz mains "hum" and harmonics are a major issue, and extensive filtering is required to reduce their level.
?
There has been some amateur experimentation at around 8kHz, and transatlantic communications, at a very low data rate has been achieved.
?
Some interesting historical notes on underground VLF antennas, including loops, can be found here.
?
?
Regards,
?
Martin
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?
On Wed, Feb 12, 2025 at 09:54 AM, John E. Burgar wrote:
I have been meaning to try an earth probe antenna here for over a year. I wanted to make one about 500' long with each end terminated by 8' copper coated ground rods.
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I think the issues is how much contribution there is from the ground path vs, the interconnecting wire laid on the surface.
?
Earth probes and amplifiers were extensively used during trench warfare in WWI, in order to eavesdrop on field telephones, that at the time used the earth as a return path for the single wire phone line. Twin wire was then introduced, and latterly the Fullerphone, with increasing development to further improve security.
?
?
The earth itself is a lossy dielectric medium, but at VLF it's mainly resistive, the ground conductivity, and underlying geology having a major effect on propagation.
?
50 or 60Hz mains "hum" and harmonics are a major issue, and extensive filtering is required to reduce their level.
?
There has been some amateur experimentation at around 8kHz, and transatlantic communications, at a very low data rate has been achieved.
?
Some interesting historical notes on underground VLF antennas, including loops, can be found here.
?
http://www.rexresearch.com/rogers/1rogers.htm#wx319
?
Regards,
?
Martin
?
?
On Wed, Feb 12, 2025 at 09:54 AM, John E. Burgar wrote:
I have been meaning to try an earth probe antenna here for over a year. I wanted to make one about 500' long with each end terminated by 8' copper coated ground rods.
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On Tuesday, February 11, 2025 at 09:20:29 PM PST, Gedas via groups.io <w8bya@...> wrote:
I have been
meaning to try an earth probe antenna here for over a year. I
wanted to make one about 500' long with each end terminated by 8'
copper coated ground rods.
When you think about it, in practice, it sort of resembles (to me)
a weird folded dipole of sorts.? A somewhat folded dipole where
the "top dipole wire" is running along on the ground surface while
the bottom dipole is a complex form comprised of the two copper
rods driven in the ground and whatever conductivity exists between
them via the soil. I might be wrong but my gut tells me that the
top dipole, the wire laying on the ground contributes quite a bit
to the antennas characteristics.
Gedas, W8BYA EN70JT
Light travels faster than sound.....
This is why some people appear bright until you hear them speak.
On 2/11/2025 11:24 PM, Facility 406
wrote:
On
2/11/2025 11:55, Everett N4CY via groups.io wrote:
What would happen if you put two ground
rods in the ground, spaced 25' to 50' apart and use an
amplifier?
I'd have to dig out some old books, but I think the Germans were
doing that, minus the amp at the time, in the 1860's.? I seem to
recall a section in one of my radio books from around 1906 having
a decent writeup on it.? It wasn't called radio yet, but was known
as wireless at the time, and detected intentional signals, but it
was the beginning.
For several decades, probes with amplifiers were the go-to.?
Probes ranged from screwdrivers stuck in the dirt in gardens, to
1m rods tens of meters apart.? Several years ago, I asked about
two probes, one about 200' deep, the other, about 500', 1/2 mile
apart.? No response.? I no longer have access to both of those
probes.? I also had the idea of a 1/2 mile loop, and up to a dozen
turns a half mile around each.? I may still play with that.
Here is some probe info:
If you can find references to the old ELF/ULF forum that was on
Yahoo, it was almost entirely discussing probes.
This one may parallel it:
/g/VLF
If not, people at the above forum may have info.
Kurt
|
Re: File upload: Rotable FLAG-antenna
On Tue, Feb 11, 2025 at 04:17 PM, Warren Dean / NI5L wrote:
Would there be any problem feeding the antenna and pre-amp with CAT-6 cable?
No, there would be no problem, this a a proven technique. Te original LZ1AQ AAA-1C? active loop is using twisted pair Ethernet cable as feedline, power supply line and control line..
?
"Ethernet cables are designed to handle frequencies that coincide nicely with most of the interesting amateur radio bands, and their insertion losses not much worse than RG58. The twisted pairs are also a balanced system that’s good at rejecting common mode noise. Cat 6 cable also has four pairs of conductors, allowing you to feed multiple antennas with one cable, or to distribute power to amplifiers and switches along with antenna feeds."
?
Video:
?
?
regards, Fred
|
I have been
meaning to try an earth probe antenna here for over a year. I
wanted to make one about 500' long with each end terminated by 8'
copper coated ground rods.
When you think about it, in practice, it sort of resembles (to me)
a weird folded dipole of sorts.? A somewhat folded dipole where
the "top dipole wire" is running along on the ground surface while
the bottom dipole is a complex form comprised of the two copper
rods driven in the ground and whatever conductivity exists between
them via the soil. I might be wrong but my gut tells me that the
top dipole, the wire laying on the ground contributes quite a bit
to the antennas characteristics.
Gedas, W8BYA EN70JT
Light travels faster than sound.....
This is why some people appear bright until you hear them speak.
On 2/11/2025 11:24 PM, Facility 406
wrote:
toggle quoted message
Show quoted text
On
2/11/2025 11:55, Everett N4CY via groups.io wrote:
What would happen if you put two ground
rods in the ground, spaced 25' to 50' apart and use an
amplifier?
I'd have to dig out some old books, but I think the Germans were
doing that, minus the amp at the time, in the 1860's.? I seem to
recall a section in one of my radio books from around 1906 having
a decent writeup on it.? It wasn't called radio yet, but was known
as wireless at the time, and detected intentional signals, but it
was the beginning.
For several decades, probes with amplifiers were the go-to.?
Probes ranged from screwdrivers stuck in the dirt in gardens, to
1m rods tens of meters apart.? Several years ago, I asked about
two probes, one about 200' deep, the other, about 500', 1/2 mile
apart.? No response.? I no longer have access to both of those
probes.? I also had the idea of a 1/2 mile loop, and up to a dozen
turns a half mile around each.? I may still play with that.
Here is some probe info:
If you can find references to the old ELF/ULF forum that was on
Yahoo, it was almost entirely discussing probes.
This one may parallel it:
/g/VLF
If not, people at the above forum may have info.
Kurt
|
On 2/11/2025 11:55, Everett N4CY via groups.io wrote: What would happen if you put two ground rods in the ground, spaced 25' to 50' apart and use an amplifier? I'd have to dig out some old books, but I think the Germans were doing that, minus the amp at the time, in the 1860's. I seem to recall a section in one of my radio books from around 1906 having a decent writeup on it. It wasn't called radio yet, but was known as wireless at the time, and detected intentional signals, but it was the beginning. For several decades, probes with amplifiers were the go-to. Probes ranged from screwdrivers stuck in the dirt in gardens, to 1m rods tens of meters apart. Several years ago, I asked about two probes, one about 200' deep, the other, about 500', 1/2 mile apart. No response. I no longer have access to both of those probes. I also had the idea of a 1/2 mile loop, and up to a dozen turns a half mile around each. I may still play with that. Here is some probe info: If you can find references to the old ELF/ULF forum that was on Yahoo, it was almost entirely discussing probes. This one may parallel it: /g/VLFIf not, people at the above forum may have info. Kurt
|
Tom, Here is another link for you
Good Evening Tom.
Here is one of them ? This is an open wire loop with no shielding for obvious?reasons because of its physical?size.
Here is another VLF antenna using a Ferrite Rod
There was a third one I recently found but can't seem to locate it at the moment.? The one with the ferrite rod ought to give you some idea of the shielding and I hope the reason for the shielding. Basically the shield reduces the electrical field and lets the magnetic field in the box.? When I find it I will?pass it along.
Fred N4cla
Fred,
Can you list the web sites that talk about this type of antenna?? I have never heard of the gap that you mention nor the shielding.
I am familiar with loop antenna but this seems very different then a normal loop?
Thank you
Tom
?
?
Tom Anderson
SDR_Radio@...
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I am thinking of making a VLF loop out of a 10 ft piece of PEX pipe with many turns of wire inside the PEX and a plastic junction box on the bottom.? I have read several articles about doing the same thing with copper pipe as the
shield and making a gap in the top center of the pipe. The purpose of the gap is to shield the windings from electrical noise and allowing the magnetic waves inside the pipe.?
There are several?articles on how to shield VLF antennas ie; Ferrite Rods, from electrical noise.? Making copper pipe loops and metal electrical boxes at the bottom and cutting a gap in the pipe at the top is basically the same as shielding
the Ferrite Rod with aluminum and leaving an air gap for the magnetic waves.? Pex is a different animal as if you cut a gap in the top of a PEX loop, you lose the round loop. So my question is this.? What if I keep the round loop attached to the plastic electrical
box and shield the entire round loop with #80 copper mesh and not the box, would I have the same shielding as an the copper pipe loop?
Fred
N4CLA
|
Good Evening Tom.
Here is one of them ? This is an open wire loop with no shielding for obvious?reasons because of its physical?size.
Here is another VLF antenna using a Ferrite Rod
There was a third one I recently found but can't seem to locate it at the moment.? The one with the ferrite rod ought to give you some idea of the shielding and I hope the reason for the shielding. Basically the shield reduces the electrical field and lets the magnetic field in the box.? When I find it I will?pass it along.
Fred N4cla
Fred,
Can you list the web sites that talk about this type of antenna?? I have never heard of the gap that you mention nor the shielding.
I am familiar with loop antenna but this seems very different then a normal loop?
Thank you
Tom
?
?
Tom Anderson
SDR_Radio@...
?
I am thinking of making a VLF loop out of a 10 ft piece of PEX pipe with many turns of wire inside the PEX and a plastic junction box on the bottom.? I have read several articles about doing the same thing with copper pipe as the
shield and making a gap in the top center of the pipe. The purpose of the gap is to shield the windings from electrical noise and allowing the magnetic waves inside the pipe.?
There are several?articles on how to shield VLF antennas ie; Ferrite Rods, from electrical noise.? Making copper pipe loops and metal electrical boxes at the bottom and cutting a gap in the pipe at the top is basically the same as shielding
the Ferrite Rod with aluminum and leaving an air gap for the magnetic waves.? Pex is a different animal as if you cut a gap in the top of a PEX loop, you lose the round loop. So my question is this.? What if I keep the round loop attached to the plastic electrical
box and shield the entire round loop with #80 copper mesh and not the box, would I have the same shielding as an the copper pipe loop?
Fred
N4CLA
|
Fred,
Can you list the web sites that talk about this type of antenna? ?I have never heard of the gap that you mention nor the shielding.
I am familiar with loop antenna but this seems very different then a normal loop?
Thank you
Tom
?
?
Tom Anderson
SDR_Radio@...
toggle quoted message
Show quoted text
On Feb 12, 2025, at 2:13?AM, Fred Moore via groups.io <n40cla@...> wrote:
?
I am thinking of making a VLF loop out of a 10 ft piece of PEX pipe with many turns of wire inside the PEX and a plastic junction box on the bottom.? I have read several articles about doing the same thing with copper pipe as the
shield and making a gap in the top center of the pipe. The purpose of the gap is to shield the windings from electrical noise and allowing the magnetic waves inside the pipe.?
There are several?articles on how to shield VLF antennas ie; Ferrite Rods, from electrical noise.? Making copper pipe loops and metal electrical boxes at the bottom and cutting a gap in the pipe at the top is basically the same as shielding
the Ferrite Rod with aluminum and leaving an air gap for the magnetic waves.? Pex is a different animal as if you cut a gap in the top of a PEX loop, you lose the round loop. So my question is this.? What if I keep the round loop attached to the plastic electrical
box and shield the entire round loop with #80 copper mesh and not the box, would I have the same shielding as an the copper pipe loop?
Fred
N4CLA
|
Re: File upload: Rotable FLAG-antenna
That's exactly what I intend to do.? :)
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73
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Look at the W1VLF YouTube channel. He has several different loops of different sizes and materials. For example a 9' x 9' loop made from hardware cloth:
?
?
On the shielded loop shielding the windings from the electric field I'm not so sure. We are talking about electromagnetic waves which are both E and H. Unless Maxwell is wrong a changing magnetic field generates an electric field (and vice-versa), so I'm not sure how you can sort one from the other. Here is a good page that talks about receiving loops. Summary is that the shield helps balance the loop and thus makes it less susceptible to common mode noise:
?
?
--
===================================================================
Mike M
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Just for the heck of it I asked AI if the ground rods would work and this is what it came back with.
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Everett N4CY
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Yes, it is possible to detect VLF (Very Low Frequency) signals using two rods in the ground connected to a preamplifier. This setup essentially forms a simple dipole antenna2. The rods act as the receiving elements, and the preamplifier boosts the weak signals received by the rods.
However, there are a few considerations to keep in mind:
-
Signal-to-Noise Ratio (S/N): VLF signals are often weak and can be easily drowned out by noise. A good preamplifier with a high dynamic range can help improve the S/N ratio1.
-
Ground Conductivity: The effectiveness of the rods can depend on the ground conductivity where they are placed.
-
Interference: Avoid areas with high electromagnetic interference, such as power lines or electronic devices.
Would you like more detailed information on how to set this up, or any specific aspects you're curious about?
https://physicsopenlab.org/2020/05/03/loop-antenna-for-very-low-frequency/
In a message dated 2/11/2025 1:41:32 PM Central Standard Time, martin_ehrenfried@... writes:
?
I think the skin depth of the various conductor types you have suggested may be an influencing factor.
?
Some of the antenna articles on the VLF.IT website could be of interest.
?
?
Regards,
?
Martin
?
On Tue, Feb 11, 2025 at 06:13 PM, Fred Moore wrote:
would I have the same shielding as an the copper pipe loop?
|
What would happen if you put two ground rods in the ground, spaced 25' to 50' apart and use an amplifier?
?
Everett
In a message dated 2/11/2025 1:51:11 PM Central Standard Time, 1rfsam@... writes:
?
Or that one:
?
On Tue, Feb 11, 2025 at 11:49?AM rfsam via groups.io
<1rfsam@...> wrote:
>
> There are also PEX lines with aluminum layer between plastic layers.
> Could be a proper candidate for shielded loop?
> Like that
> Not cheap though.
> Simon
>
> On Tue, Feb 11, 2025 at 11:44?AM W0LEV via groups.io
> <davearea51a@...> wrote:
> >
> > You could cover your PEX with a continuous layer of a good conductive material like copper mesh or copper (bronze) screen.? But be sure to introduce the break at the top of the loop.? I believe PEX is nonconductive.? With the screen or mesh, it should act much like using a copper tube.
> >
> > Dave - W?LEV
> >
> >
> > On Tue, Feb 11, 2025 at 7:41?PM Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote:
> >>
> >> I think the skin depth of the various conductor types you have suggested may be an influencing factor.
> >>
> >> Some of the antenna articles on the VLF.IT website could be of interest.
> >>
> >>
> >>
> >> Regards,
> >>
> >> Martin
> >>
> >> On Tue, Feb 11, 2025 at 06:13 PM, Fred Moore wrote:
> >>
> >> would I have the same shielding as an the copper pipe loop?
> >
> >
> >
> > --
> > Dave - W?LEV
> >
> >
> >
>
>
>
>
>
?
?
?
?
|
Or that one: On Tue, Feb 11, 2025 at 11:49?AM rfsam via groups.io <1rfsam@...> wrote:
There are also PEX lines with aluminum layer between plastic layers.
Could be a proper candidate for shielded loop?
Like that
Not cheap though.
Simon
On Tue, Feb 11, 2025 at 11:44?AM W0LEV via groups.io
<davearea51a@...> wrote:
You could cover your PEX with a continuous layer of a good conductive material like copper mesh or copper (bronze) screen. But be sure to introduce the break at the top of the loop. I believe PEX is nonconductive. With the screen or mesh, it should act much like using a copper tube.
Dave - W?LEV
On Tue, Feb 11, 2025 at 7:41?PM Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote:
I think the skin depth of the various conductor types you have suggested may be an influencing factor.
Some of the antenna articles on the VLF.IT website could be of interest.
Regards,
Martin
On Tue, Feb 11, 2025 at 06:13 PM, Fred Moore wrote:
would I have the same shielding as an the copper pipe loop?
--
Dave - W?LEV
|
Warren Dean / NI5L
Everett N4CY