Fwd: Fw: [VLF] 8270 Hz propagation chart

[Jonathan]

Hi All,

I had to share this plot created by a member of the VLF community. He modeled 8270 Hz (that's 8.270 kHz) propagation vs distance during both daytime and nighttime Earth-ionosophere waveguide. I find it so fascinating!

The thread below mentions the model parameters and a very interesting interaction with two waveguide modes and the modal interference at a certain distance from the transmitter. I've seen similar modal interference with Navy VLF transmitters that are a long distance away. 

For those that may not be aware, 8270 Hz is significant because it's used for amateur VLF transmissions. Unlike HF, VLF waves propagate in a waveguide created by the Earth's surface and the D/E layers of the ionosphere. Like waveguide used in microwaves transmission, VLF waves excite various waveguide modes, and unlike in microwave transmission (at least normally), the waveguide parameters are continuously changing throughout the diurnal. 

Jonathan

---------- Forwarded message ---------
From: Jonathan <mr_inte...@yahoo.com>
Date: Sun, Jun 22, 2025 at 7:15 PM
Subject: Fw: [VLF] 8270 Hz propagation chart
To: emum...@gmail.com <emum...@gmail.com>

Sent from Yahoo Mail for iPhone

Begin forwarded message:

On Sunday, June 22, 2025, 6:12 PM, alves thierry via groups.io <elf_ehf=engine...@groups.io> wrote:

Hello,

I have made a chart showing the signal decrease on the 8270 Hz band for daytime and nightime considering an homogeneous ground with er=15 and s=0.001 S/m. During daytime, only the first mode is excited. At night the first mode suffers less attenuation, probably because the waveguide cutoff is somewhat lower than in daytime.

Notice that in nightime a second order mode is also excited resulting in a modal interference with maximum effect at 350 km from the transmitter. Probably some of you have already noticed that effect comparing day/night signal. So yes, if you are at this distance, daytime signal is greater !

Above 1000 km, the nightime second mode suffers to much attenuation, only the first mode remains, as a result here nightime signal is greater, "as usual".

73 from Thierry.

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[Bill Liles]

Thanks, Jonathan. Are there any details of the model used?

Bill

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[Lawrence Naif]

Nice, where did he get the data? Perhaps we can map that to the state of the ionosphere above if we know that exact date and time of observations and map it to S4, RFI, TEC measurements, across 192 GPS-LEO configurations.

Check the attached video.

Best Regards,

[Steve Cerwin]

That is very cool Jonathan. That deepest null looks just like the multipath WWVB nulls we looked at a couple of years ago. Like those, I bet there is a 180-deg phase shift at the bottom. 

73, Steve 

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From: ham...@googlegroups.com <ham...@googlegroups.com> on behalf of Jonathan <emum...@gmail.com>
Sent: Sunday, June 22, 2025 7:55 PM
To: Unknown <ham...@googlegroups.com>; hamsc...@googlegroups.com <hamsc...@googlegroups.com>
Subject: [HamSCI] Fwd: Fw: [VLF] 8270 Hz propagation chart

 

[Jonathan]

Bill,

I'm almost positive that it's the LWPC model, but I'm getting confirmation.

Lawrence,

This isn't a plot of data, this is a plot of what is more than likely an LWPC model output. One thing to keep in mind is that the tools you've mentioned don't apply to VLF. Traditional ionospheric measurement and sounding tools don't adequately provide information on the D layer. One technique is to use VLF signals such as sferics and VLF transmitters. To get large scale measurements, you need a lot of VLF receivers, and that is one thing I'm trying to work towards.

Steve,

I completely agree! I would definitely wager that it is a ~180 degree phase shift. I think this and WWVB are examples of model interference with !180 degree phase shifts.

Jonathan

To view this discussion visit https://groups.google.com/d/msgid/hamsci/PH7PR10MB64839FFBBDC824DB79F65AA1DC79A%40PH7PR10MB6483.namprd10.prod.outlook.com.