Can you transmit radio signals through a metal tube?

[rasen58]

Is it possible to transmit radio signals through a metal tube?
If I have on transceiver in the middle and I want to communicate with my station at the end of the tube, would that be possible?

I know that it wouldn't work if the station was outside the tube entirely because the radio waves wouldn't be able to go through the steel because it would act like a faraday cage, but would it still be possible through the length of the tube?

 

[teufler]

I would say 800 mhz quarter wave, something that you could have that would not touch the sides of the pipe. I think you could even have a 90 degree bend in the pipe. Now for what purpose, I don't know but should work. Maybe even a quarter wave uhf or vhf, again if it was placed inside the tune and the antenna would not touch the sides of the pipe. Receiving, with the tube fiberglass or pvc, it could transmit as many antennas, for a base are designed like that.

 

[mmckenna]

Yes, it's called a waveguide.

 

[nd5y]

Yes. That is known as a waveguide. Normally they are rectangular instead of a round tube.
A circular waveguide tube diameter would have to be at least .59 wavelength at the lowest frequency.
http://www.w1ghz.org/QEX/circular_wg.pdf
http://www.rfcafe.com/references/electrical/waveguide.htm

 

[Voyager]

The above two comments are exactly what I was going to reply.

 

[Token]

Is it possible to transmit radio signals through a metal tube?
If I have on transceiver in the middle and I want to communicate with my station at the end of the tube, would that be possible?

I know that it wouldn't work if the station was outside the tube entirely because the radio waves wouldn't be able to go through the steel because it would act like a faraday cage, but would it still be possible through the length of the tube?

A little more detail would help. Is this an existing tube? What is the diameter of the tube? What kind of distances are you talking about? How far are you trying to go?

As others have pointed out, a circular tube can be used as waveguide. In certain modes of operation they can be very low loss. This mode of operation is determined by the diameter of the tube vs the wavelength of the frequency used. That does not mean it cannot be used at lower frequencies, however depending on a few factors the loss (efficiency of the energy transfer) can get very high. In fact, waveguide can make a pretty good filter

As a specific example, to use FRS radios in such an application the tube would have to be roughly 3 feet across to do it efficiently. Smaller diameter might work, but losses would go up as size goes down.

For small diameter tube I have had reasonable luck turning the tube into a low efficiency coax.

For example I wanted to talk from one underground location to another, about 200 meters apart. And as an experiment I did not want to put up antennas, and I wanted to minimize the RF that could be detected at distance. There was a one inch ID metal water pipe between the two locations. This was far to small a diameter for anything but microwave frequencies, and even then the surface irregularities of the pipe would make it a poor waveguide.

I used a vacuum cleaner to draw a pilot line (string) through the the pipe, then I used the pilot line to pull an insulated single conductor wire through. I then inductively coupled this wire to an FRS radio at each end (that means basically I wrapped the wire around the antenna of each radio without making a solid electrical connection). Communications between the two locations was fine, and was hard to detect above ground unless you were right on top of either location.

T!

 

[rasen58]

Thanks everyone.
For more detail, the tube has a diameter of around 2.23 m (> 7 ft) and will travel for let's say 20 miles.
There will be some slight turns as well, but as @teufler said, 90 degree bends should be fine as well?

I'm not sure if the radio waves will be able to continue for that many miles, so would repeaters have to be used?

 

[prcguy]

As coincidance I've been running elliptical waveguide and installing flange connectors over the last few days, but its too small for scanner freqs and made for the 6GHz range.
prcguy

 

[mmckenna]

We've spent a huge amount of time at work trying to find solutions to solve in building cellular telephone coverage.
There are a number of solutions, but one of the most interesting ones we heard about was a group talking about using HVAC ducting as a simple waveguide. Bi-directional amplifier, femto-micro-pico-cells or a direct iDAS system could place antennas at strategic points inside a building HVAC system to distribute signals. Better solutions have come along, but it's an interesting idea. Of course air dampers, coils and the like would get in the way, but in most cases that could be designed around. Bonus what that almost every office/room had it's own "waveguide" port in the ceiling.

Similar to the antenna-in-a-tube idea, and most HVAC ducts are suitable for lower cellular frequencies.

 

[ab3a]

If this is a permanent installation, you might want to consider something a bit different.

Generally, in tunnels, the practice is to use inline amplifiers and leaky coaxial cable to enable VHF radios to communicate. The Andrew corporation makes such a transmission line; I believe it is called Radiax. The problem with this approach is that it does get a bit expensive with mile after mile of this expensive cable. However, it is the right tool for the job. It is often used in subway tunnels. It can support many connections.

In the long run, it may be cheaper than setting up numerous femto or pico cells but I haven't run the numbers recently, so I can't say this is still the case today.

 

[krokus]

Thanks everyone.
For more detail, the tube has a diameter of around 2.23 m (> 7 ft) and will travel for let's say 20 miles.
There will be some slight turns as well, but as @teufler said, 90 degree bends should be fine as well?

I'm not sure if the radio waves will be able to continue for that many miles, so would repeaters have to be used?

Do you need communications just at the ends, or also at locations along the way?

Sent via Tapatalk