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noob coax question - RF Cafe Forums

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crossection
 Post subject: noob coax question
Posted: Sun Oct 05, 2008 2:14 pm 
 
Lieutenant

Joined: Sun Oct 05, 2008 12:44 pm
Posts: 1
Location: CA
Apologies if this isn't the right forum for this question...

I need to build a coaxial line that will have perforations in the outer conductor to allow me to see the interior. The visual access section will be about an inch in length, and the coax is built from 1.5" i.d. copper tube (outer conductor) and 0.375" copper rod (inner conductor).

Perforations will be small - about 1mm diameter on 4mm pitch arrayed around and along the 1" sight section. Frequency is 2.45 GHz, so the perforations are small compared to the wavelength (dielectric is air).

My question is whether I'll have significant radiation from the perf'ed section - significant would be ~1% or more of the incident power. I have successfully used perforations to give nonradiating visual access in rectangular waveguide (symmetric hole patterns centered on the short wall).

My math says that a coax wall won't radiate under these conditions, but since I've never worked with coax before, I don't have full confidence in my math model. I'd like to get another opinion before I cut metal and maybe warm up the room in an unanticipated way!

Thanks for your help.


 
   
 
WA9WVX
 Post subject: Radiating Coaxial Feedline
Posted: Wed Dec 24, 2008 12:13 am 
 
Captain

Joined: Mon Jul 07, 2008 9:42 pm
Posts: 7
Location: Northern, IL
Sounds like you want to re-invent Andrew's Radiax Coaxial RF Cable. This has also been known as Leaky Line. This 50-Ohm RF cable has been available for 40 or 50 years and is heavily used in large multi-level buildings such as: hospitals, hotels, downtown offices, football, Basketball, baseball, horse racing stadiums, museums and tunnels. The RF cable allows signals to penetrate areas where outside antennas are unable to reach marginal or dead spots within the buildings and it allows the signals to work both ways in a two-way radio communications system.

Andrew is now a division of Commscope and here's their website:

http://www.commscope.com/andrew/eng/product/trans_line_sys/coaxial/radiating/1206639_13611.html

73,

Dan
WA9WVX




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