Hi; A modestly high impedance between the mast and the tower will send more of the current down the feedline, thus increasing the voltage at the lightning arrestor, suppressor, or attenuator (of cour
Hi, Pete; Don't worry about the 100,000 amp strike. The average lightning stroke is 18,000 amp and lasts for something like a microsecond. The killer strikes, the 10% capable of lots of damage, have
Nylon deteriorates when exposed to UV. If you use it for guys or anything else outdoors, plan to inspect it often and replace it occasionally. I'm not sure how to determine that its strength is not r
A few years ago, I had money to spend and asked for info for modeling with ELNEC. AEA responded with data and hints. A prominent, but surviving antenna seller insisted his antennas were the very best
Hello to all; I also modeled a 3.5 wl wire using EZNEC and observed exactly what Pete reports at .5 and at 1.0 wl above ground. It is moderately directional, with the strongest signal in an arc off e
Hi, Steve and all; ARRL handbooks provide formulas and graphs for calculating inductance and designing coils. "The approximate inductance of a single layer air-core coil.... L = d^2 times n^2) &divid
Hello, Jim, Jim, and all; Jim is correct in calculating the loads and questioning the adequacy of the roof and joist structure. He is also correct in questioning his recollection of wind force: use 4
Hello, again; I forgot to mention in my earlier response, engineering handbooks are available in the references of many librarys. Libraries that don't have them may be able to borrow them. Some libra
Hi, Danny; Radials under some vertiacl antennas serve to reduce ground losses or, in the case of elevated verticals, serve as part of the antenna (refer to Jerry Cevik's discussion on his web site).
Work hardening and metal fatigue are not the same. Metal fatigue affects aluminum, copper, steel, and other metals. It does not occur unless the applied stress exceeds a threshold value. Correct desi
Regarding corroded bolts in towers. It is advisable to inspect the hardware every 5 years or so and replace any that is deteriorating. Stainless steel is superior but may be hard to find or very expe
Joe, Dan, and all; I confirm Dec 84 QST includes an excellent article about traps constructed of coax. I built a pair for 40M with RG-58 on 2.5" plastic pipe and they have been in service since 94. T
Hello to all; I appreciate the information Tod, KØTO, provided regarding his experience refurbishing an aluminum tower. I wonder if loose pins in place of bolts holding sections together adequ
Be careful heating alloys, lest you weaken them. Universal uses 6063-T832 for the legs. I don't know the max to which it may be heated without altering it, but I'm sure this information is available,
Regarding grounding and an RF service entrance: Parallel conductors spaced apart provide low inductance similar to that provided by flat conductors, as described in Polyphaser's book and other source
The drag force on a cylinder perpendicular to the wind (and other forms) is given by: Drag = Cd X 1/2 X density of air X area X velocity squared. (D = Cd*.5*rho*A*V^2) Cd, coefficient of drag, is a f
It appears to me the 'forked radial' may have merit under vertical antennas taller than 1/4 wave, where the maximum current appears higher than the base and where the maximum reflected ground current
Hi, Frank; You are correct that there is a reason not to drain the tubes. Alkalinity of the concrete protects steel from corroding. Drainage permits the alkalinity to leach out, after which the steel
10,000 at one site in a single night? That number discredits the report, in my opinion. Think of the pile of that many dead birds. Ever find a victim under your tower? I've heard similar reports abou
Hi, Mark; Good information is available in PolyPhaser's book and in the application notes from ICE. For a tower not at the corner of your building fan out at least five radials counting two that are