Towertalk
[Top] [All Lists]

## Re: [TowerTalk] Grounding base slab and pier tower bases

 To: "Roger D Johnson" , ,"Jim Lux" Re: [TowerTalk] Grounding base slab and pier tower bases "Michael Tope" Tue, 4 Jul 2006 17:58:04 -0700
 ``` ----- Original Message ----- From: "Jim Lux" To: "Roger D Johnson" ; Cc: Sent: Tuesday, July 04, 2006 1:36 PM Subject: Re: [TowerTalk] Grounding base slab and pier tower bases > Now, let's look at the reactance of that C, at, say, 100 kHz (a standard > lightning impulse is 2 microsecond rise and 50 microsecond fall, so let's > say that it's like 100 kHz). X=1/(2*pi*100E5*80E-9) = 1/(2*pi*8000E-4) = > 1/(6*0.8) = 1/5 -> 0.2 ohms.... That's pretty low.. MUCH lower than the > resistive impedance to the earth from a ground rod (5-20 ohms). With that > 20 kA impulse, you're looking at a 4 kV voltage drop, which isn't all that > huge. Given that the rise time is actually much faster, and the reactance > lower, the voltage will be less. > Here is a practical question you UFER guys. I am planning to have some front yard hardscaping done in the next month or so (concrete retaining wall, steps, pilasters, etc). My thought was that following excavation and prior to the pour for the new concrete, I would lay down a fairly dense radial field for my short 160 meter vertical. The radials would start at the base of the vertical and then fan out into the front yard: http://www.dellroy.com/W4EF's-Ham-Radio-Page/Radial_Project/Radial.htm Originally I was planning to have the existing driveway slab demo'd and replaced but due to cost constraints, I've decided to keep it as is. Unfortunately, if I keep the existing driveway slab as planned, the front yard radials for the 160 meter antenna will have to be cut short about 20 feet of reaching all the way across the front yard (see illustration above). The UFER discussion got me to thinking that perhaps I could somehow tie the ends of the front-yard radials into the edge of the existing driveway slab so that could get some additional RF grounding benefit as compared to letting the front-yard radials stop just short of the slab. So the question is, how would I go about attaching the ends of the radials wires to the edge of the slab in a way that would provide a low resistance/reactance connection to the slab? I have a bunch of 3/8 diameter "Red Hat" concrete anchors left over from another project, so one thought was to use these to provide the connection. The Red Hat's wouldn't provide much actual contact area, however, as the only place where there is significant contact force between the metal and the concrete would be under the head of the hex-nut/washer and the wedge on the end of the anchor. Anyway, I would be interested in suggestions on how best to make these connections (or if its even worth bothering with). BTW, I should mention that my main goal for the radial system is to lower the losses of the radial system in order to raise the antenna efficiency. I am on dry rocky soil here with a less than ideal radial field arrangment (antenna on side of house), so I am looking for every last drop of efficiency that I can squeeze out of the system. As far as lightning protection goes, I am in Southern California, so this isn't a big concern. Thanks, Mike W4EF............................................ _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] Grounding base slab and pier tower bases, Nick Pair Re: [TowerTalk] Grounding base slab and pier tower bases, JC Smith Re: [TowerTalk] Grounding base slab and pier tower bases, Jim Lux Re: [TowerTalk] Grounding base slab and pier tower bases, Nick Pair Re: [TowerTalk] Grounding base slab and pier tower bases, Roger D Johnson Re: [TowerTalk] Grounding base slab and pier tower bases, Jim Lux Re: [TowerTalk] Grounding base slab and pier tower bases, Roger D Johnson Re: [TowerTalk] Grounding base slab and pier tower bases, David Robbins K1TTT Re: [TowerTalk] Grounding base slab and pier tower bases, Roger D Johnson Re: [TowerTalk] Grounding base slab and pier tower bases, Jim Lux Re: [TowerTalk] Grounding base slab and pier tower bases, Michael Tope <= [TowerTalk] Using a Concrete Slab as Part of Vertical Counterpoise?, Michael Tope Re: [TowerTalk] Grounding base slab and pier tower bases, Roger D Johnson Re: [TowerTalk] Grounding base slab and pier tower bases, Jim Lux Re: [TowerTalk] Grounding base slab and pier tower bases, Nick Pair