How far can rf signals transmit in the pipe?

[tony_lth]

Hi, Gurus,
In the power supply pipe, there are some power supply cables, which maybe 20KV.
I want to transmit radio signals in the pipe.
I can use 470M or 2.4G in the pipe, 2.4G may have better anti-noise performance, but its transmit distance may be short.
So which would be better in the curve pipe?

And in the curve pipe, which antenna would be fitful and have small size?
Best,
Tony Liu

 

[vfone]

Similar with the other post you opened (transmitting RF signals using power lines), transmitting RF signals in such mediums to get a steady communication link, depends by so many factors (compared to a freespace radio communication) that I don't know if somebody can give (or even predict) a good answer.

 

[PlanarMetamaterials]

Hi Tony,

Are you looking at using the power cables as part of the RF transmission scheme? If you're just using the pipe itself, you'd need to be using a circular waveguide mode, which will only propagate depending on frequency, pipe radius, and fill factor of the pipe.

 

[volker@muehlhaus]

Is that a metal pipe? Think of it as a circular waveguide.

Signals can propagate if frequency is above the "cutoff frequency". Use this calculator to check cutoff frequency:

Circular Waveguide Calculator

www.everythingrf.com

 

[BigBoss]

If you can find a Very High Voltage Capacitor , why not.
This technique is used for much lower frequencies ( few kHz) since years.Electric grid distribution centers have been using this method to communicate.

 

[FvM]

Is that a metal pipe? Think of it as a circular waveguide.

Most cable pipes are made of plastic, e.g. PVC. Wave is dissipated into the ground.

 

[tony_lth]

Hi, Gurus,
Many thanks for the reply.
I have asked one my friend to help me, who is an antenna engineer.
Who will do some simulation for me, on the propagation loss.
I want to clarify the idea: using 2 power cables' shieldings, one as the signal, and the other as the GND, without any contact on the cables. Not TRX inside the cable as PLC did.
The idea is some weird, but I can't wait to know the results.
I will let you know the simulation results.
Best,
Tony Liu

 

[FvM]

Medium voltage cable has copper wire shield which is basically good for RF transmission, but you have typically arbitrarily varying cable spacing and in case of underground plastic pipe also huge losses. At the discussed 2.4 GHz, the transmission might be also disturbed by multiple wave modes.

 

[PlanarMetamaterials]

Who will do some simulation for me, on the propagation loss.
I want to clarify the idea: using 2 power cables' shieldings, one as the signal, and the other as the GND, without any contact on the cables. Not TRX inside the cable as PLC did.
The idea is some weird, but I can't wait to know the results.
I will let you know the simulation results.
Best,
Tony Liu

How long of a distance are you looking at propagating over? What are the specs on size of the cables and size of the pipe (is the pipe metallic)?

 

[tony_lth]

Hi, Gurus,
My friend built a 300mm length model, and found the min loss is 2dB.
So that means, for a 100dB loss, this method can only transmit 15 meters.
I am looking for a km level propagating. And now we are trying KHz, because the data rates are very low.
Best,
Tony Liu

 

[FvM]

You didn't yet answer basic questions, e.g. about pipe material.

 

[tony_lth]

The pipe is underground pipe, which may be concrete, for some power 20KV cables, and size is 1M*1M.

 

[volker@muehlhaus]

I think RF is the wrong media for this case. Over here, they installed fiber optics on the top end of underground pipes (sewer lines). Sounds weird, but works very nicely.

 

[biff44]

there are papers on RF communications in mine shafts. I would find some of those and see. i recall a few miles were achieved

 

[tony_lth]

Hi, @biff44,
Thank you very much.
After simulation, I found low frequency RF surely can reach KMs.
But it would be much better if refering your papers.
Best,
Tony Liu