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RF signals in tunnels - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Below are all of the old forum threads, including all the responses to the original posts.

-- Amateur Radio
-- Antennas
-- Circuits & Components
-- Systems
-- Test & Measurement

 Post subject: RF signals in tunnels
Posted: Wed Oct 05, 2005 7:53 am 

I read somewhere (maybe on RF Cafe) about special "leaky" coaxial cable that is used in tunnels to broadcast signals. Do you know if this is only used for things like AM/FM radio and emergency channels, or can it also be used for cell phone signals?

How about does anyone know of specific instances where it is being used now? I'm thinking about a SBIR (Small Business Innovation Research) project proposal for Homeland Security and want to get as much info as possible, including where it is actually working now.


 Post subject:
Posted: Wed Oct 05, 2005 11:25 am 
User avatar

Joined: Mon Jul 18, 2005 4:31 pm
Posts: 43
Location: Baltimore, MD
Leaky coax is very old technology that has been used for years. Yes, it is currently used for cell phones and pagers in subway tunnels all over the place.

You will be able to get some examples from some of the vendors. Andrew calls theirs "Radiax" and Times Microwave also has a product. I'm sure there are others.

 Post subject:
Posted: Wed Oct 05, 2005 12:48 pm 
Thank kanling, I'll look there.


 Post subject:
Posted: Mon Jun 02, 2008 4:36 am 

Joined: Mon Jun 02, 2008 2:29 am
Posts: 1
Hi Leo
I saw your post on the RF Cafe. Did you manage to find more information about leaky coax cables. I am working on a 868 MHz antenna and is interest in any kind of information on this subject.


 Post subject:
Posted: Mon Jun 02, 2008 8:23 pm 

RFS also has this cables, I've used them on a subway line and they worked pretty well..

They call them "Radiaflex":

You'll find more info on the catalogs.


 Post subject: Leaky Cable Vs Fiber Optic
Posted: Mon Oct 27, 2008 5:50 pm 

Joined: Mon Oct 27, 2008 5:32 pm
Posts: 1
Location: Los Angeles, CA
kanling is right. Leaky cables are very old technology. Some companies started using fiber optic cable to transmit signals and build repeater stations along the way.

Your solution for RF over Fiber

 Post subject:
Posted: Wed Oct 29, 2008 4:46 am 
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 304
Location: London UK
Hi Leo
The 22 mile-long Channel Tunnel between UK and France supports all emergengy communication for the trains and response services using a "Leaky Feeder" coaxial system for VHF and UHF. The system was put in by a JV between Motorola and Andrew Antenna Corp. many years ago (during tunnel construction work in 1987).
More modern approaches certainly focus on fibre-optic cables with drop/insert modems whereby the optical side is directly modulated /demodulated with the full radio spectrum, then a small antenna radiates the radio signal locally (eg TETRA). A power feed is obviously necessary on copper cables bundled with the optical fibre.

 Post subject:
Posted: Thu Oct 30, 2008 6:58 am 
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 304
Location: London UK
Hi Leo
Two further afterthoughts:
1. You might find some interesting, although probably "academic" treatment of the topic in IEEE Trans. 1986 EMC-28 (3) a paper entitled "Experimental Study of Radio Characteristics in an Underground Street and Corridors" by Yamaguchi, Abe and Sekiguchi.
2. There is a report in the British amateur radio journal RadCom of tests at VHF, UHF and 1300MHz done in connection with emergency services and the National Rail Network in the UK. I will try to locate the reference date. I recall it concluded that 1300MHz was a very effective part of the spectrum for free radiation through concrete-lined rail tunnels to support rail accident rescue operations.

Posted  11/12/2012

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