TTers:
I'm very sympathetic with Wayne. In south west
Colorado (Pagosa Springs) my home sits on
bedrock. All 5 acres of my property is bedrock
under just a few inches of soil. When it cam
time to put up the tower, I discovered that the
best I could do was go down about 6
inches. Fortunately, the rock was virtually
contiguous with very few fractures. I removed
the dirt, drilled 25 holes into the bedrock, and
cemented re-bar in place with industrial grade
cement. From there, I made a frame, poured the 5
yards of concrete, and the tower is up and works fine.
Grounding is another challenging issue. Based
upon discussions with local old timers who worked
on microwave relay sites in the Rocky Mountains
around here, I went with the copper strap headed
away from the tower and aimed away from the house
approach. I employed a"Ufer" ground, and added
lots of radials around the tower (about 60
total). The coax shield is grounded at the top
of the tower, at the base of the tower, and at
the shack, as are the SteppIR antenna and rotator control cables.
I use I.C.E. protectors on all circuits and
grounded everything at the tower, as well as at
the single point ground outside the house by the
radio room. It was quite a challenge to do it
all, and the initial approach concerned
me. However, it seems to be working fine. I've
just had one strike, and I need to replace one of
the I.C.E. protectors. Fortunately, that's all.
My web site describes in words and photos what I did:
http://home.centurytel.net/WD0M/
Click on Ham Radio, then either the Tower or
Lightning Protection link, depending upon your
interest. Good luck to all the other "grounding
challenged" hams out there! I'm sure there is
more I can/could/will do, and thanks to all who
share their experiences and suggestions here on TT.
73,
Joe
WDØM
At 12:02 PM 8/3/2005, Wayne Greaves wrote:
>Steve,
>
>I have similar poor soil (e.g., rock) conditions at my QTH in south-central
>New Mexico. While excavating the foundation for my second tower I hit a
>very solid layer at only 18 inches that required a jackhammer and clay spade
>attachment to bust through. I'm down to four feet now and ideally have one
>more foot to go.
>
>This tower will be 200 ft. away from the house. Ground rods are impossible
>to pound in by hand here(although my power company did install one next to
>the meter pole). My solution for providing a ground for this tower will be
>to bury two radials of 1-1/2 inch wide 26 ga. copper strap about 6 inches
>below grade. Each radial will be 50 ft. long and extend in opposite
>directions from the tower base. The copper strap attaches to the tower
>using Polyphaser TK-4 clamps, which prevents the copper from being in direct
>contact with the galvanized steel base (dissimilar metal issue). Ideally,
>the strap should also be connected to ground rods spaced every 16 ft. or so,
>but that simply is not going to happen in my case. In theory this design
>should provide a low impedance path to dissipate electrons into the earth.
>Copper strap is more effective than solid copper ground wire because the
>large surface area of the strap better exploits the skin effect.
>
>The tower being 200 ft. from the shack is advantageous because the
>inductance in the feedline will slow the pulse risetime as it travels down
>the coax allowing the ground system to bleed off more charge before it
>reaches the shack. In addition, the coax braid will be bonded to the tower
>at two points, top and bottom.
>
>I must take exception to your not grounding the coax bulkhead to your house
>ground. In my opinion, disconnecting the entry coax from the bulkhead does
>not guarantee that strike energy won't get into your house. After traveling
>thousands of feet to that point, a few more inches won't make any
>difference. Furthermore, if the bulkhead is not bonded to your house ground
>then during a strike event there will be a significant difference of
>potential between the bulkhead and the house and current will find a way
>flow (bad). If instead the bulhead and house ground are tied together, the
>two points will be at the same potential and will rise and fall
>simultaneously, a much preferred situation.
>
>Best of luck!
>
>73,
>Wayne, WØZW
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|