[Amps] 2 more questions-- electrical

[Roger (sub1)]

On 4/5/2011 12:47 PM, Jim Brown wrote:
> On 4/5/2011 7:59 AM, Bill, W6WRT wrote:
>> REPLY:
>>
>> If you are getting RF in the shack, you do not have a grounding problem,
>> you have an antenna problem. You do NOT need an RF ground at your shack
>> in any way. The only grounds your shack needs are for safety of the AC
>> mains and for lightning.
>>
>> RF in the shack problems indicate an unbalance in the antenna and/or
>> feedline system and can almost always be cured by proper application of
>> a balun or unun.
>>
>> RF energy is expensive to generate. Do not waste it by running it
>> through dirt. Get it up in the air where it belongs.
> RIGHT!
>
> Back to Charles's question about which ground is better.  The answer is
> that it doesn't matter -- ALL MUST BE BONDED TOGETHER, which makes them
> effectively in parallel.  In addition to lowering the impedance to
> earth, that also reduces the potential difference between different
> points in your building in the event of a lightning event, which in turn
> minimizes the likelihood that something is going to fry.
>
> As to the power company's ground rods -- THEY DON'T MATTER! LIGHTNING IS
> NOT A DC EVENT, it is an IMPULSE, with VERY STRONG harmonics. The energy
> in lightning  is broadly centered around 1 MHz, so what matters is the

I would add "broadly centered" may cover an order of magnitude, but the 
farther out you go the fewer outliers you find.  Even the super strikes, 
or positive lightning will not vary much outside that range even though 
the power contained in the harmonics may be substantial compared to a 
typical strike.  It might help some to think of lightning as a really 
dirty 1 MHz signal<:-))

A typical strike may induce over 1000 volts per meter in a conductor, be 
it an antenna, coax, telephone wire, or even house wiring. In a home 
that's say, 75 or 100 feet long including garage the voltages induced at 
one end of the building could be as much as 20 or 30 thousand volts 
different from wires at the other end of the home.  That makes common 
grounds and common paths for wires entering the home essential.

Just to keep it interesting my shop North wall is a good 160 feet from 
the South wall in the house. They are also on separate underground 
electrical feeds but from the same pole.  There are 2 computers in the 
shop tied into the wired network with CAT6 cable and a telephone cable. 
The network and telephone runs are each 130' long.  They are also tied 
into the ham stations in the house and shop. All electrical grounds are 
tied into the ground system for the towers and electrical feeds to both 
buildings. That system consists of a network of  33 8' ground rods and 
over 600 feet of bare #2 copper plus the two electrical system ground 
rods at each service entrance for a total of 37 ground rods although the 
ones required by code at the entrances are relatively anemic compared to 
the rest of the ground system.

73

Roger (K8RI)

> IMPEDANCE of the path to ground, which, if you do the arithmetic, is
> dominated by the  INDUCTANCE of the connecting wires.
>
> 73, Jim Brown K9YC
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>