[RFI] Single-point grounding

Pete Smith N4ZR n4zr at contesting.com
Mon Jul 2 06:02:22 PDT 2012


I actually took a third path - the computer with the RS-232 connection 
is attached to my ground bus no more than an inch from where the 
transceiver's chassis is connected, and both ground leads are no more 
than a foot of #0 wire.  My hope is that this loop will then be small 
enough that the voltage rise will be minimal.

73, Pete N4ZR
The World Contest Station Database, at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000

On 7/2/2012 7:35 AM, David Robbins wrote:
> short = straight
> bends = not shortest path
> loops = multiple bends
>
> a widely published lightning expert who advises me has told me that he knows of no reason why bends are bad for lightning ground except for the case where jumping a gap from a bent wire to something nearby been observed.  sharp corners provide a place where the electric field can more easily breakdown an air gap... hence the observations that lead to the misconception that lightning doesn't turn corners.
>
> one thing to watch for if you have problems like pete's with control circuits is the unintentional loop that is closed by the control signal cable.  loops can develop large induced voltages from nearby strikes, and the bigger the area of the loop the higher the voltage... so consider two options, if you run a baseboard ground behind the tables like i do and take separate vertical connections up to a radio and a computer that are on opposite ends of a table you get a big square loop closed by the rs-232 cable... but if you run one conductor up from the baseboard to the radio then continue it over to the computer essentially parallel to the rs-232 cable you get a much smaller area between the conductors.
>
>
> Jul 1, 2012 04:17:18 PM, eddieedwards at tconl.com wrote:
>
> Jim Brown wrote:
> "IEEE research says that the energy in lightning is very broadly centered
> around 1 MHz, with lots of energy at least a decade of frequency above and
> below. At these frequencies, impedance is dominated by inductance, not
> resistance. Thus short is better."
>
> To keep impedance/inductance as low as possible, I've heard that all bonding
> connections should not only be short, but also should not have any sharp
> bends or turns. Nothing tighter than an 8"-10" radius bend. Greater than
> 10" radius bends if possible. And no loops. Keep it as short and straight
> as possible.
>
> 73, de ed -K0iL
>
>
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