Topband: Adding a Ground to Elevated Feed Vertical?
herbs at vitelcom.net
Tue Nov 29 13:44:57 PST 2011
On 11/29/2011 5:08 PM, Mark Adams wrote:
> I've been running my vertical for a couple of weeks now and it plays very
> nicely. The setup is:
> 85' up and 42' horizontal.
> Comtek 1:1 balun at feedpoint 7' off ground.
> 3 x ~137' radials all between 7 and 13 feet (driveway crossing height) off
> the ground.
> Fed with good coax.
> VSWR at rig end of coax is 1.9:1 at 1830 kHz.
> The question is whether it is worthwhile to install a ground rod under the
> feedpoint and connect the neg side of the balun to the ground rod (or maybe
> the shell of the 259 at the bottom of the balun). I'm asking because with
> my luck I won't be able to remove the rod once it is in and I cannot
> convert this antenna to ground radials because it is close to my driveway.
> OK, I could rent/borrow a horizontal boring rig.....
> Mark K2QO
> K2 #543
Mark, An earth ground at the point you mentioned is valuable, not so
much because of any change of the feed point impedance as a result, but
since this ground can provide provides a protection against lightning.
The way you have described it a lightning bolt or strike would need to
travel back to you shack and rig to find a path to ground. Having an
earth ground at the feed point and a proper choke for draining of static
build p on the inverted L is well worth the effort. If you find the
impedance change is gong the wrong way you could place the requisite
windings between the coax and the earth ground to isolate the RF ground
from the electrical ground and still have the value of the protection.
I am sure most would agree the actual change in radiation resistance all
depends on the ground type and conductivity.
Herb Schoenbohm, KV4FZ
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