[Lowfer] grounding active antennas

[Steve Dove]

Hi Doug,

Bear in mind that outer of the feedline to an e-probe is 
part of the antenna;  it's not just the little bit poking 
out the top.

This has two important implications:  Firstly, any noise on 
that feedline, which can of course extend all the way back 
to the shack and which is then connected to the always 
delightfully clean AC power distribution beyond, is 
connecting *directly into the antenna*.

The second is that the longer and higher that feedline, the 
bigger the overall antenna becomes, the bigger the signals 
it receives.  It's not the height, per se, it's that it is 
now a bigger antenna!

It is usually recommended to ground the coax coming down 
from the e-probe as soon as it hits dirt;  this can do a 
huge amount for reducing the feeder-borne noise, shunting it 
to ground before it hits the antenna system, and is the 
first thing to try.  Better the ground the better  - 
electrical service grounding rod, or copper pipe hammered in 
are good.  It isn't necessary to run a separate ground wire 
up to the e-probe  -  using the coax outer is superior in a 
couple of respects.

This  -  grounding the feedline where it hits dirt  -  is a 
good start to defining what then is actually the antenna, 
and what is feedline;  the bit going up from ground to the 
e-probe and the whip itself constitute the antenna (mostly), 
the bit from the grounding point back to the shack becomes 
feedline (mostly), just like Mother Nature intended.

So, that's the first thing to try.  Reducing those 'mostlys' 
further involves a common-mode choke on the feedline as it 
heads for the shack at the grounding point, and isolating 
the feedline and the phantom-powering source from shack 
ground in the shack, using transformer(s).  But more on 
these when you've tried grounding the feedline.

         Cheers,

                 Steve


http://www.w3eee.com




Douglas D. Williams wrote:
> Well, mine is on a 15 ft high tv antenna mast. The mast is galvanized, not
> painted, so it would be a fairly simple matter for me to drive a copper rod
> at the base of the mast, connect the mast to the rod, then connect the coax
> shield to the mast at the top. Might be worth a try to see what happens. 
> 
> -----Original Message-----
> From: lowfer-bounces at mailman.qth.net [mailto:lowfer-bounces at mailman.qth.net]
> On Behalf Of ToddRoberts2001 at aol.com
> Sent: Saturday, May 26, 2007 11:52 AM
> To: lowfer at mailman.qth.net
> Subject: Re: [Lowfer] grounding active antennas
> 
> In a message dated 5/26/2007 11:27:51 AM Eastern Standard Time, 
> iguana at chartertn.net writes:
> I am looking for opinions on whether or not active e-probe vlf/lf antennas
> should be grounded at the antenna location. Assume the antenna is located 50
> ft or more from the receiver and that the receiver has a good ground.
> 
> -Doug KB4OER
>  
>  
> Hi Doug,
>        In my experience I have found getting the active e-probe vlf/lf 
> antenna as high above ground level as practical helps more than anything
> else. I 
> have my active antenna hoisted up into a pine tree about 40 ft high and
> noticed a 
> big reduction in noise level AND a big increase in signal levels, compared
> to 
> the same antenna ground-mounted 5ft above ground level. 
>        There is no practical way to ground the antenna hoisted up in a tree 
> but mine works very well using the station ground back at the receiver end. 
>        If the antenna is mounted at ground level best thing to do is 
> experiment with a remote ground at the antenna and see if it helps.
> Everyone's 
> situation is different so remote grounding may help sometimes but not
> always.
>        73 Todd WD4NGG
>