[Elecraft] Grounding negative side of power supply?

Mon Apr 19 20:36:29 EDT 2010

To Tom, Bill and all:

I never said anything about a "direct" strike.  Don't bother trying to 
protect for a direct strike.   Nothing will survive a direct strike.

The problem is two ground points, separated by some distance of earth be it 
5 ft, 50 ft or 500 ft.  During a nearby strike the energy from the nearby 
strike is dissipated largely across the surface of the earth up to a depth 
of some 18" to 24".  Due to resistance between the two ground points and the 
energy flowing through the earth there will be a difference in potential 
between the two points.  Now, with the radio connected between the receiving 
antenna and the AC mains, the path for the current difference is through the 
radio and power supply.

It's your radio, it's your choice.  You decide.

73
Bob, K4TAX

----- Original Message ----- 
From: "Tom W8JI" <w8ji at w8ji.com>
To: <rmcgraw at blomand.net>; "Bill Coleman" <aa4lr at arrl.net>
Cc: <elecraft at mailman.qth.net>
Sent: Monday, April 19, 2010 12:03 AM
Subject: Re: [Elecraft] Grounding negative side of power supply?

> This appears to be a question from January 20, 2010, so it
> is a little late, but a person never wants to connect the
> ground rod of the K9AY antenna or any other small or low
> receiving antenna to the mains ground.
>
> First, it would kill the advantage of having the antenna. If
> you are going to do that, don't bother installing the
> antenna. It will hurt the antenna in more than one way.
>
> Second, it is not necessary for safety. It is not a large
> tall structure and is not likely at all to be involved with
> a direct lightning hit, and even if it were hit the ground
> at the cable entrance to the house would provide all the
> required protection.
>
> The shack ground and the antenna entrance ground should be
> bonded to the mains, but the K9AY or any other low noise
> receiving array must have an isolated ground. The cable
> leaving the receiving antenna should be buried, should have
> common mode isolation, and should be grounded at the house
> entrance to a ground that is bonded to the mains ground.
>
> 73 Tom
>
>
> ----- Original Message ----- 
> From: "Robert Mcgraw" <rmcgraw at blomand.net>
> To: "Bill Coleman" <aa4lr at arrl.net>
> Cc: <elecraft at mailman.qth.net>; <don at w3fpr.com>
> Sent: Sunday, April 18, 2010 10:35 PM
> Subject: Re: [Elecraft] Grounding negative side of power
> supply?
>
>
> Yes, do provide a driven ground for the K9AY receiving
> antenna.  This is
> required for lightning protection.  AND be sure to bond this
> ground to
> the AC mains ground for the house.  Failure to do this will
> produce a
> voltage difference or step voltage between the two ground
> during a nearby
> lightning strike.  The voltage difference can be enough to
> damage or
> destroy the radio connected between the antenna and the AC
> power.  AND,
> bonding of all grounds to a common point is a requirement of
> the NEC.
>
> Remember, lighting has traveled through several thousand
> feet of air.  A
> balun will offer little to no protection in this regard.
> Now placing a
> choke balun or a 1:1 current balun at the feed point will
> reduce common
> mode noise on the coax feed line.
>
> 73
> Bob, K4TAX
>
>
>
>>
>> On Jan 20, 2010, at 11:47 PM, Richard S. Lindzen wrote:
>>
>>> Dear Don,
>>>
>>> This leaves me a bit concerned.  I am planning to put up
>>> a K9AY
>>> receiving antenna in my backyard and it is supposed to be
>>> connected
>>> to a ground rod.  I had never seen it suggested that this
>>> must be
>>> connected to the utility ground stake.  I'm not even sure
>>> where the
>>> utility ground stake is.  I've never noticed one though I
>>> will ask my
>>> electrician.  If there is one, it is likely to be pretty
>>> far from the
>>> K9AY.
>>
>> For the K9AY, your best bet is to make sure the antenna
>> ground and the
>> coax ground are completely isolated. I do this by
>> magnetically coupling
>> the coax with a 9:1 transformer. Otherwise, common-mode
>> noise can move
>> out the shield and be picked up by the antenna.
>>
>> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
>> Web: http://boringhamradiopart.blogspot.com
>> Quote: "Not within a thousand years will man ever fly!"
>>             -- Wilbur Wright, 1901
>>
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