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Re: [RFI] Fixing Pin 1 Problems

To: RFI RFI <rfi@contesting.com>
Subject: Re: [RFI] Fixing Pin 1 Problems
From: dalej <dj2001x@comcast.net>
Date: Thu, 13 Jan 2011 15:31:01 -0600
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
Thanks Jim.

I will have a look at your tutorial.  

The old TV sets of a few years ago are/were most troublesome.  We have new sets 
here and they are miles apart as far as RFI goes from the old sets.  I checked 
my cabling to the external boxes and it appears pin one of the XLR does go to 
chassis of the two external boxes. I have them in a rack which the rails are 
taken to station ground.  So far I have no RFI issues now on 10, 15 or 20, 20 
being my worst case band for RFI here.  I also have many #31 and 43 mix 
snap-on's all over everything.  BTW, I burnished the paint off the surface 
where the rack ears attach to the Behringer box.  I felt that paint might be 
preventing a good RF ground to the rack ears.  I also installed a couple of 
split cores on internal cabling from the front panel to the rear PCB which 
holds all of the XLR/TRS receptacles.   

Dale, k9vuj

On 13, Jan 2011, at 14:08, Jim Brown wrote:

> On 1/12/2011 2:49 PM, dalej wrote:
>> How would I cure a pin one problem in a particular piece of equipment.  
>> Would I look at the input XLR or TRS and put that pin one directly to ground 
>> or the chassis somewhere close to the receptacle?
> Let's stop confusing things by using the word "ground" when we talk 
> about a connection to the chassis, or to circuit common.  The key info 
> here is that common mode current, usually, but not always shield 
> current, needs a complete circuit (or an antenna). Our objective is to 
> provide a path that does NOT include circuit common, thus keeping it 
> outside of equipment.
> Low frequency current usually finds a path to the earth, or to the power 
> system equipment ground (Green Wire), and NEC REQUIRES that the the 
> Green wire go to the chassis of equipment, and to the earth at panel 
> where power enters a building.  Thus, a connection to the CHASSIS (or 
> more correctly, the SHIELDING ENCLOSURE) for all cable shields, return 
> of power cables, solves that problem. That is, all the common mode 
> current stays outside the box.
>>  What about the PCB?  Some of those doggone connectors are mounted to PCB 
>> and not that easy to find the pin one connection.  I like the theory, but 
>> implementation is another matter, in some cases.
> YES, that's exactly the root CAUSE of most pin 1 problems, and because 
> of the way stuff is built, they are usually VERY difficult to fix 
> without rebuilding and rewiring equipment (and perhaps causing more 
> problems than you solve).  In those situations, the best solution is 
> usually to simply kill the current on that cable, either with a common 
> mode choke, or by diverting the current to a lower impedance path.  
> Common mode chokes are most effective at RF, while diversion is usually 
> most effective at audio and power frequencies. Both are typically needed 
> on telephone equipment (including voice phones and DSL modems).
> RF current is on those cables because they are acting as receiving 
> antennas. At high frequencies, no earth connection is needed to provide 
> a return path for that antenna current -- the local wiring within a ham 
> shack, or an A/V rig, or even the chassis of equipment may be large 
> enough as a fraction of a wavelength to be the other half of the antenna.
> There is a lot of tutorial material on my website about this.  The Power 
> Point on Ham Interfacing, and the Solving Problems In the Shack chapter 
> of the RFI tutorial, address the audio frequency solutions. The RFI 
> tutorial also includes lots of detail about how ferrite chokes work, and 
> how to use them to kill RFI coupled by pin 1 problems.
> http://audiosystemsgroup.com/publish.htm
> Two sets of people need to understand all of this, and the two must 
> react to it differently.  Those of us who USE equipment must usually 
> work around those problems with band-aids like diversion and ferrite 
> chokes, and by making sure that our stations and systems are properly 
> bonded together, to the earth, and to the power system.  Those who 
> DESIGN and BUILD equipment must BUILD IT DIFFERENTLY!  In 1994, when the 
> pro audio world was first alerted to the Pin 1 Problem by Neil Muncy 
> (ex-W3WJE), a very good pro audio mfr called Rane acknowledged the pin 1 
> problems in their gear, and over a period of about five years made 
> running production changes to all of their more than 50 products to 
> eliminate them. When that transition was complete, they found that their 
> customer support costs, most of which addressed  problems with hum, 
> buzz, and RFI, had dropped by 90%!
> 73, Jim Brown  K9YC
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