Re: [TenTec] RFI Issues

["Bob McGraw - K4TAX" <RMcGraw@Blomand.net>]

For vertical antennas, not vertical dipoles, ground radials at 1/4 
wavelength and number about 32 is most adequate.  More than this in terms of 
length or quantity has shown little to no signal improvement in the AM 
broadcast world.  Even alternating between 1/4 wavelength and 1/2 wavelength 
radials makes little to no difference.  It is however a nice advantage to 
put a ground screen or mat of suitable size depending on frequency at the 
base of the vertical as this area has the highest ground current flow. 
Ground radials should be attached to the ground ring around this mat.
As to radial spacing, equally spaced is best assuming space and structure 
permit such. It makes for a nice omni directional pattern.  Otherwise, put 
radials in the ground what and where you can.  One can't get too many 
although there is a point of diminishing return for the work and investment. 
Typically 8 to 12 radials 1/4 wave will be great for most ham applications.
You are correct on the vertical 1/2 wave dipole, assuming you can get the 
feed line perpendicular to the antenna at the feed point elevation and it 
runs at least 1/4 wavelength horizontally away.  Try that on 160M!
73
Bob, K4TAX

----- Original Message ----- 
From: "John" <jh.graves@verizon.net>
To: <tentec@contesting.com>
Sent: Thursday, May 17, 2012 10:31 AM
Subject: Re: [TenTec] RFI Issues


> Bob,
>
> Aside from  1/2 wave verticals (or vertical end fed dipoles if you will)
> not needing radials as they are as complete as a  horizontal dipole
> also, with a 1/4 wave vertical, is it not sufficient to have a number of
> closely spaced short  radials rather than several radials a 1/4 wave
> long at the lowest frequency? I thought I had read that radial spacing
> may be more important than length and that radials may not have much
> effect past the 1/4 wave point. Although the thought of establishing
> (consuming the back yard) as a RF base for a vertical antenna is
> certainly interesting.
>
> John / WA1JG
>
>
> On 5/17/2012 7:59 AM, Bob McGraw - K4TAX wrote:
> > Just visualize that your 30 ft length of wire from your station to 
> > "ground"
> > puts your station near the HV point or nearly 1/4 wave above ground for 
> > 40M.
> > If one has RFI issues on one band and not on others, this could likely be
> > the reason.
> >
> > I agree with Jim on all of this.   Many antenna systems require a ground
> > reference for radiation efficiency AND lightning protection.   And all of
> > this should be outside of the structure, NEVER inside!
> >
> > At the same time, a center fed dipole or a beam is in itself a complete
> > radiating system and requires no ground at all to be an efficient 
> > radiator.
> > On the other hand, antennas such as verticals, end fed wires, slopers to
> > name a few do work against earth/ground which serves as the other 1/2 of 
> > the
> > antenna system.  This is the reason radials are typically used with
> > verticals be they at the surface of the earth or elevated as in a ground
> > plane antennas.
> >
> > RFI issues are typically the result of wiring within the station, acting 
> > as
> > an antenna itself, picking up RF as radiated from the transmitting 
> > antenna
> > or antenna loads that produce a highly reactive condition at the station.
> > In both of these cases, grounding is not the solution.
> >
> > I also don't subscribe to the idea of a tuned ground system or artificial
> > ground.  For one, tuning will change from band to band and in some cases
> > frequency within the wider bands.  Also, as one described, radials of
> > various lengths spread around the room can have quite high voltage at 
> > their
> > ends which in itself can produce some nasty RF burns or contribute to
> > accidents or fire.
> >
> > 73
> > Bob, K4TAX
> >
> >
> >
> > ----- Original Message -----
> > From: "Jose F Ballester"<jfballester@gmail.com>
> > To:<k9yc@arrl.net>; "Discussion of Ten-Tec Equipment"
> > <tentec@contesting.com>
> > Sent: Wednesday, May 16, 2012 9:57 PM
> > Subject: Re: [TenTec] RFI Issues
> >
> >
> > > I'm 30' from a copper plated ground rod connected with a 10 gauge 
> > > braided
> > > copper wire from my second story shack.   Never detected a difference 
> > > when
> > > it has been disconnected.   Don't have grounded antennas.
> > >
> > > Why is it necessary?
> > >
> > > 73 de Pepe WP3HW
> > >
> > >
> > > On May 16, 2012, at 10:49 PM, Jim Brown wrote:
> > >
> > > On 5/16/2012 12:22 PM, Stuart Rohre wrote:
> > > > Likely with a second floor shack, ONLY the tuned ground lead would help
> > > > your RFI.
> > > Repeat after me:
> > >
> > > A CONNECTION TO EARTH HAS NOTHING TO DO WITH RFI.
> > >
> > > A CONNECTION TO EARTH HAS NOTHING TO DO WITH RFI.
> > >
> > > A CONNECTION TO EARTH HAS NOTHING TO DO WITH RFI.
> > >
> > > A CONNECTION TO EARTH HAS NOTHING TO DO WITH RFI.
> > >
> > > A CONNECTION TO EARTH HAS NOTHING TO DO WITH RFI.
> > >
> > > A CONNECTION TO EARTH HAS NOTHING TO DO WITH RFI.
> > >
> > > A CONNECTION TO EARTH HAS NOTHING TO DO WITH RFI.
> > >
> > > A CONNECTION TO EARTH HAS NOTHING TO DO WITH RFI.
> > >
> > > A CONNECTION TO EARTH HAS NOTHING TO DO WITH RFI.
> > >
> > > What matters is proper bonding of cable shields to the chassis of the
> > > equipment to which it is connected, and the proper bonding of every
> > > equipment chassis to each other.
> > >
> > > 73, Jim K9YC
> > > _______________________________________________
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