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Re: [RFI] RFI Report Re: IOTA DLS-45 w/IQ4 Charger-PS

To: rfi@contesting.com
Subject: Re: [RFI] RFI Report Re: IOTA DLS-45 w/IQ4 Charger-PS
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Mon, 21 Mar 2011 23:39:24 -0700
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On 3/21/2011 7:57 PM, Christopher E. Brown wrote:
> The green wire in the AC cable bonds the the inside of the steel chassis
> and the circuit board, the chassis bond is on the outside.  Bonding the
> outside lug to the same gnd as the power plug corrected things for me.

I find the description a bit confusing, BUT -- I suspect a problem with 
PAINT preventing an electrical contact between the green wire and the 
chassis.  The inside of the chassis and the outside of the chassis 
SHOULD be the same point. Further, the green wire in the AC cable MUST, 
by law, go to the chassis.

There CAN be magnetic coupling of noise from a switching power supply to 
the outside world, but that is NOT what gets fixed with the ground lug.

In general, it is NOT a good thing to bond V- to the chassis of the 
power supply.  The reason is that doing so can couple the IR drop on the 
V- lead to accessory equipment that is powered from same supply. When 
running SSB that IR  drop will sound like SSB detected by an AM 
detector, which in turn will show up as distortion in the transmitted 
signal.  Bonding V- to the chassis also can couple buzz from power line 
leakage currents to the audio signal.

If I were you, I would carefully scrape the chassis at the point where 
the green wire connects to make sure it is making good contact, but I 
would remove any connection between V- and the chassis.

73, Jim K9YC
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