[Boatanchors] Burying Coax

[hwhall at compuserve.com]

My belief 
is or was that the outer shield forms a capacitor with the inner conductor 
and therefore a noise signal on the outer braid will to some extent 
capacitivily couple itself into the center conductor. 

 The inside ofthe shield indeed forms capacitance with the center conductor, but theoutside of the shield cannot do so, it cannot "see" the centerconductor. RF skin effects keep the currents flowing on the outside ofthe shield from passing through the shield to flow on the inner side ofthe shield. So, as long as everything (e.g., connectors, etc.) wasassembled correctly, the RF noise on the outside of the shield shouldnot be able to get inside. 

Having said all that, the coax shield will NOT prevent inductively coupled signals (e.g., varying magnetic fields) from getting through the shield . However, such magnetically coupled signals should affect the shield and center conductors alike, sort of like a balanced line, and thus not cause a net signal voltage to appear across the conductors. There may be a voltage found if either inner or shield conductors are compared to ground, however. If there's any way that your station might allow that to happen, then there might (or might not) be something gained from burial. I imagine the effectiveness of burial, if any, would also depend greatly on depth and the conductance of the soil.

If it wasn't so much digging, burying the line would be a wonderful experiment. I wonder if a shorter run to a closer-by temporary antenna would be sufficient to test the idea?

Wayne
WB4OGM

 

-----Original Message-----
From: Keith Densmore <kmd at xplornet.ca>
To: Boatanchors <Boatanchors at mailman.qth.net>
Sent: Thu, Dec 8, 2011 7:52 am
Subject: Re: [Boatanchors] Burying Coax


Thanks to all you great guys with the information on the ditch witch. Sounds 
like that will do it. Glad there is a machine for that, hi.

But a couple of you mentioned that burying coax will not lower noise pickup. 
Which has caused me to put this plan on hold. I need to know more.

I 'thought' coax to be a good insulator of noise but not perfect. My belief 
is or was that the outer shield forms a capacitor with the inner conductor 
and therefore a noise signal on the outer braid will to some extent 
capacitivily couple itself into the center conductor. In my case the antenna 
is in a low noise location but the coax runs through a noisier area. I 
listen to 40 meters down to VLF, VLF being very prone to AC line noises.

Anyone know for sure?

Thanks, 73,
Keith


______________________________________________________________
Boatanchors mailing list
Home: http://mailman.qth.net/mailman/listinfo/boatanchors
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Boatanchors at mailman.qth.net

List Administrator: Duane Fischer, W8DBF
** For Assistance: dfischer at usol.com ** 


This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html