[Antennas] Log Periodic

[George, W5YR]

Myles, the problem here is what "ground" means in the instructions you
mention. To me, that means do not allow the coax braid or the boom that it
is feeding to be connected to anything about the actual tower or mast.
Since all that is many feet above actual earth ground and the tower itself
may be making relatively poor contact with earth ground, I doubt that you
are being cautioned against running a "ground" wire from the shield down
the tower to earth ground.

Actual connection of the shield to earth ground at the line input should
not cause a problem and may be recommended for lightning protection
purposes, but I will leave that to the esxperts.

It is unfortunate throughout the history of radio, etc. that "ground" was
ever introduced as a term for "connection to a <whatever> that is a neutral
potential reference." We speak of grounding things within a circuit when we
are actually talking about connecting something to the system "ground" or
reference point or whatever. Connection to an actual earth ground is
neither meant nor intended. Guess it all started when it was decided that
since one side of the power line which is earth-grounded for safety
reasons, it could for convenience be connected to the chassis of the
equipment and all signal and power returns made to that point. 

To your point, though, I think that it is clear that "ground" in the
context above refers only to the physical antenna itself, the coax
connection there, and the tower, etc.

73/72/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437
 

Myles Byrne wrote:
> 
> I have a KMA-1330  HF Log  Periodic 18 ft boom 8 element (13 to 30 mhz) - love the antenna it does a good job... The antenna uses a twin boom separated from each other by insulated material. One boom is the center of the coax the other boom the shield - feed through a bead balun.
> I Have been told  (instruction book states this) and convention dictates that the feed point (front of the Log) should not allow that the shield touch ground. The entire antenna is isolated from the mast by the insulated material also. Where along the feed line is it ok to ground the shield - a few feet, 10 20 100 etc feet - it is now grounded at a remote switch box at the base of a 75 foot tower. I have had the Log in the air for about 2 years, and it works well, but have always wondered about the grounding of the shield of the coax.