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Re: [TowerTalk] Station Ground

To: "Tower Talk List" <>
Subject: Re: [TowerTalk] Station Ground
From: "Jim Brown" <>
Reply-to: Jim Brown <>
Date: Sat, 15 Jan 2005 20:00:03 -0600
List-post: <>
On Sat, 15 Jan 2005 18:46:37 -0500, K8RI on Tower Talk wrote:

>But what do you do with equipment like the Icom 756 Pro that uses the mike 
>shield as a neutral return to the PC board?

I think you mean it uses the shield as the signal return for the mic. The 
answer is that still connect the shield to the chassis. At audio frequencies, 
the circuit board will be at ground potential unless you do something stupid 
like connect a shield to it. (and it's Icom that did it stupid). 

>This is an old house and who knows where all the wiring goes, but I'd bet 
>dollars to donuts there is a floating neutral *somewhere* on a circuit in 
>the house.  I can say with a pretty strong certainty it isn't on either 
>circuit in this room.

I'm not sure what you mean by a floating neutral. As we've been saying, the 
neutral gets bonded to ground once. Do you mean that a neutral and hot (phase) 
conductor are reversed somewhere?  That IS a common wiring mistake, and it's 
important that you chase it down. A voltmeter or good outlet tester will tell 
you. You should always read very low voltage (less than a volt) between 
neutral and the ground pin, and you should always read close to 120 volts 
between the ground pin and hot. 

There was a company called ECOS, located in a suburb of Chicago, that made 
great outlet testers. The company is long gone, but the testers come up pretty 
often on EBay for not a lot of money. They do a quick accurate test of an 
outlet, and you can push a button and read the resistance from the ground pin 
back to the neutral on a meter. 

>> called "audio ground" or "control ground" on the mic connectors and the 
>> rear
>> panel jacks. One sure sign of a pin 1 problem is an RCA or 1/8" jack that 
>> is
>> insulated from the chassis. The easy cure is to remove the shield from 
>> that
>The socket is grounded to the chassis.

Excellent. So tie the mic cable shield to the connector shell. 

Jim Brown  K9YC


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