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Author Topic: Why does medium wave radio cut out when going through a tunnel?  (Read 16610 times)

Offline tommya300

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Why does medium wave radio cut out when going through a tunnel?
« Reply #25 on: 29/09/2010 05:37:21 »
is it simply because the wavelength of FM matches the entrance of the tunnels so it diffracts/bends around corners better?
I am having a bit of difficulty trying to verify this.
Can you help me find any creditable information to back this up?
Please display a URL that will lead me to this, highly curious
I thought I seen something about 5 meters referring to what you are saying, but I can not seem to find it again
« Last Edit: 29/09/2010 05:41:31 by tommya300 »
 

Offline tommya300

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Why does medium wave radio cut out when going through a tunnel?
« Reply #26 on: 29/09/2010 06:07:51 »
Here is the bit about AM/FM. I'm afraid it's all a bit anecdotal.

"They also wanted to put in AM/FM radio over the airways and rebroadcast in the tunnels, so we had to provide for all four of those," Chen said. "Any time you have four different RF sources, the chances of having co-channel interference is higher."

To avert problems, the carrier created specially made cross-band couplers to eliminate interference. But the challenges did not end there. Chen said AT&T also had to adhere to power limitations. If it put more power into the system than Bell Atlantic or the Port Authority did, it would create interference."

From: http://connectedplanetonline.com/wireless/mag/wireless_trouble_tunnels/

The artical covers real issues in multiple close communication systems.
 RF Cross talk, maintenance, population of equipment, real estate.

Leaky Coax usage attempts on Mining tunnels safety regulations

Here is some backup for you Geezer...
http://www.cdc.gov/NIOSH/Mining/pubs/pdfs/j0199048.pdf
« Last Edit: 29/09/2010 06:15:32 by tommya300 »
 

Offline mcjhn

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Why does medium wave radio cut out when going through a tunnel?
« Reply #27 on: 29/09/2010 19:08:21 »
is it simply because the wavelength of FM matches the entrance of the tunnels so it diffracts/bends around corners better?
I am having a bit of difficulty trying to verify this.
Can you help me find any creditable information to back this up?
Please display a URL that will lead me to this, highly curious
I thought I seen something about 5 meters referring to what you are saying, but I can not seem to find it again

sorry no data to back it up, it was a v.short answer (with no more explanation than that) from Dr Karl on a Australian science phone in program to the same question
http://www.drkarl.com/home/ [nofollow]

(N.B. not Dr Karl Kennedy from neighbours)

but you get the same effect in multistory car parks (FM better than AM that is)
« Last Edit: 29/09/2010 19:09:59 by mcjhn »
 

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Why does medium wave radio cut out when going through a tunnel?
« Reply #27 on: 29/09/2010 19:08:21 »

 

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