[BC] Ground system

[Milton Holladay]

OK, I'll bite !
Yes, four radials, gull wing connected, supported from the bottom of the 
tower, which put the connection point ~five feet above ground.  The 
radials were supported by short lightpoles (readily available, as this 
was not too long after Hurricane Hugo); and were, as I said, #6 hard 
drawn copper powerline wire (same comment.)
IIRC, the tests were done on 920 with 1000 watts;  the tower was not at 
its ultimate height, and the station was changing frequency to 920.  ( I 
recall that the R was 11 Ohms, so it was likely 920 rather than 1410, 
the old frequency.).  The other towers were not yet present, nor was any 
buried ground system. The soil is sandy and in the FCC's 2 conductivity  
zone, I believe.  Nearly all of SC is either 2 or 4, on the map, but 
really is much less, probably a quarter of that.
I don't recall the height of the radials--mebbe eight feet--, but after 
a bunch of measurements, they were moved up to mebbe twelve or fifteen 
feet and some more measurements were made.  ISTR that there was no 
noticeable difference.
M

On 2/12/2012 15:15: VIRUS ALERT!, Phil Alexander wrote:
> This was William Culpepper's original design. A few years ago while
> I was in Charlotte for an AM Transmission Seminar and Radio Show
> I had privilege of discussing this topic in detail with William. He
> told me that 9 deg. was a first experimental approximation that
> worked so well he felt there was no point in trying other heights.
> I believe this testing was done with 4 radials, but perhaps Milton
> can settle that point because I believe he was there.
>
> There are various theories about vertical profile of the wires, and
> some sentiment supports a "gull wing" profile. The disadvantage of
> this configuration is the high RF voltage inherent at the wire ends.
> Keep in mind that economic efficiency is an equally important target
> to radiation efficiency. IIRC, modeling I did shortly after my talk
> with William seems to support the idea of using a conventional (i.e.,
> 3 ft. AGL) drive point with a 45 deg ground wire departure angle up
> to a point 9 deg AGL extending 90 deg from the tower to an insulator
> 9 deg AGL. It can be seen that the near (tower end) support can be a
> point between 2 insulators in a short guy cable while the far support
> can be an insulator supported by a utility pole.
>
> Another point demonstrated by modeling is that galvanized guy cable
> does not appear to reduce radiation efficiency unreasonably although
> Cu jacketed steel wire (i.e., Copperweld) is somewhat superior, but
> may not be economically justifiable especially when maintenance
> factors in some geographic areas (e.g., coastal) are considered.
>
> Phil Alexander, CSRE, AMD
>

-- 
Milton R. Holladay Jr. / miltron at att.net
Columbia, S. C. / 803-331-8059
RF Measurements / Planning&  Installation / Emergency Service&  Parts