Except in this case, assuming the shield is intact and good quality, we are dealing with undesired currents flowing on the surface of the cable shield only. At 100 MHz and assuming an aluminum foil shield in the cat5, the shield metal is thicker than a few skin depths (about 8 um skin depth). So we essentially have a solid conductor in open air, and if the insulation's relative permittivity is close enough to 1 to neglect (should be), the velocity factor is close to 1.
-- Patrick Shoemaker From: [email protected] [mailto:[email protected]] On Behalf Of Greg Ihnen Sent: Wednesday, April 13, 2011 21:32 To: WISPA General List Subject: Re: [WISPA] Ethernet Cable for FM Tower Install In space (vacuum). Cables have a velocity factor. On Apr 13, 2011, at 8:42 PM, Patrick Shoemaker wrote: And speed of light (c) = 300,000,000 m/s -- Patrick Shoemaker From: [email protected]<mailto:[email protected]> [mailto:[email protected]] On Behalf Of Patrick Shoemaker Sent: Wednesday, April 13, 2011 21:10 To: [email protected]<mailto:[email protected]>; WISPA General List Subject: Re: [WISPA] Ethernet Cable for FM Tower Install Wavelength (m) = speed of light (m/s) / frequency (Hz) Avoid ΒΌ wavelength multiples. -- Patrick Shoemaker From: [email protected]<mailto:[email protected]> [mailto:[email protected]] On Behalf Of Scott Carullo Sent: Wednesday, April 13, 2011 14:54 To: [email protected]<mailto:[email protected]>; WISPA General List Subject: Re: [WISPA] Ethernet Cable for FM Tower Install Get with someone who can tell you exactly how long to make the cables. You don't want them any whole fraction of the FM wavelength freq or it will compound your problem. Make them as de-tuned length as possible. I've had a coax in my hand not hooked to anything in the vacinity of a high-power FM station and it was a resonant length and it got so hot I had to drop it. Scott Carullo Technical Operations 855-FLSPEED x102 [http://www.flhsi.com/files/emaillogo.jpg] ________________________________ From: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Sent: Wednesday, April 13, 2011 9:39 AM To: [email protected]<mailto:[email protected]> Subject: [WISPA] Ethernet Cable for FM Tower Install We are mounting close to a 50kW FM antenna and want to use heavy, double shielded cable for the runs to the APs since we've seen issues in the past. Fiber up the tower but will need 3-4 ft jumpers to the APs. Any recommendations? -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: [email protected]<mailto:[email protected]> Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: [email protected]<mailto:[email protected]> Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
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