[Antennas] Ground?

[K1TTT]

What the station 'ground' does is keep everything in the room at the same
voltage... this is easy at 60hz, the power line 3rd prong is designed to do
that for safety.  That is why any separate ground wires from the 3rd prong
have to be tied back to the service entrance also... to keep everything at
the same voltage so you can't touch the case of two pieces of equipment and
get shocked.

At rf it is harder because the size of the room can be a large fraction of a
wavelength so the voltage at one end may be different than the other end.
What is worse is if there isn't an efficient way for the current you send
out on the center of the coax to get back to the inside of the shield and
back to the radio.  With a 'balanced' antenna that is done by the two halves
having equal currents... with a vertical with a good ground plane under it
the ground plane provides an efficient method of getting the current back to
the inside of the shield.  Wen things get out of balance, or the ground
plane isn't good enough, the outside of the shield serves as the return
path.  Now, where does the outside of the shield get the current?  It can
pick some of it up from directly coupling to the rest of the radiating part
of the antenna, this is common in dipoles and V's where the feedline doesn't
come off perpendicular or in ocf's that are inherently unbalanced.  In a
worse case the current flows through the ground to the only other collection
point it can find, the station ground, which then flows back through the
case of the radio to the shield and back out to the antenna feedpoint.  In
the worst case there isn't a good enough connection from the 'ground'
(meaning soil and/or power system ground) back to the radio, as would be the
case if you disconnected your ground from the power line, and the nearby
radiating element generated bigger induced voltages and current trying to
get back to the return point.  Thus you get more interference and more rf
problems.

Remember, at the end of the coax the currents must balance, even if some of
that current has to come through you to get to it.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
 

> -----Original Message-----
> From: Philip (KO6BB) [mailto:ko6bb at sbcglobal.net]
> Sent: Sunday, June 28, 2009 19:42
> To: Tom Horton
> Cc: Antennas
> Subject: Re: [Antennas] Ground?
> 
> Tom et al,
> Well, first I didn't expect a lot of snide remarks (not referring to this
> message but to others), but guess I should have expected them anymore.
> 
> True, my antennas DON'T require a ground to effectively radiate, the
> Butternut HF-2V and homebrewed 20M 1/4 Wave vertical both have ~1200 Sq/ft
> of sheetmetal under them, creating an effective groundplane, and the
> balanced dipole certainly doesn't need it.
> 
> HOWEVER, this mobile home park is quite a noisy place, RF wise, I suspect
> mostly carried over the underground powerlines etc (probably even the
> neutral line).  The present ground system is a daisy chain of long and
> short
> rods and it has a HUGE effect on the noise floor here, from VLF all the
> way
> through the HF range and even at 2M!
> 
> IF I disconnect the ground line from my under-bench copper buss where
> everything (including computer tower) is tied together and ONLY use the
> service ground provided by the Electrical company, the noise floor goes up
> sharply, the radio drives the computer bananas when transmitting, etc
> (computer is totally unaffected when the outdoor ground is intact).  Of
> course, because of my extensive audio work, I have a LOT more peripherals
> on
> my computer than most folks do, 8 USB devices connected, 2 USB hubs, 2
> monitors,sound equipment, radio cat, etc.  When the ground system is
> intact
> the radios don't bother any of it.
> 
> This isn't meant as a flame, but, if as you say, you've never really used
> an
> effective ground system, you may just not realize what it's doing or not
> doing?
> 
> 73 de Phil,  KO6BB
> http://ko6bb1.multiply.com/ (My OTR Blog)
> http://www.qsl.net/ko6bb/   (Web Page)
> 
> DX begins at the noise floor!
> RADIO: Yaesu FT-2000.
> Antennas:  Butternut HF-2v,  88' Ladder-Line fed dipole.
> Merced, Central California, 37.3N 120.48W  CM97sh
> 
> ----- Original Message -----
> From: "Tom Horton" <k5iid at sbcglobal.net>
> To: <antennas at mailman.qth.net>
> 
> 
> > Ground? What's a ground?
> > Seriously, I have operated for years with a ground and years without a
> > ground. Never have I ever had more than one 8 foot copperclad rod
> pounded
> > in and then usually not very deep.
> > My last QTH was on the second story of a house built in 1910 and a
> ground
> > would have been 50 feet long. So I didn't bother. I have never really
> > noticed a difference one way or another.
> > I can just imagine all the firestorms coming my way now!
> > Tom, K5IID
> 
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