[WriteLog] RFI and Keyers

Joe Subich, W4TV w4tv at subich.com
Mon Nov 12 13:12:48 EST 2007


Jim, 

To follow up on this one time ... 

> I've also seen a number of posts on the NCCC list from good 
> engineers who have fixed stability problems with Microham 
> products using ferrite chokes on interconnect wiring. That 
> fix would not work (or be necessary) if he was right. 

Others may have fixed alleged problems with "microHAM products" 
by adding ferrite chokes on the interconnect wiring but they 
are masking a problem that lies elsewhere much like an "antenna 
tuner" masks problems at the antenna by applying matching at the 
transmitter. 

The "Pin 1" issue is in the computer - specifically the USB 
port - and not the microHAM product.  If you check most of 
the consumer computers these days you will find several red 
flags for Pin 1 problems.  First, the USB connector shield is 
often not connected to the motherboard ground plane and not 
connected to the metal case of the computer (if the case is 
metal).  In addition, the USB Power return (circuit ground) 
is not connected to the power supply "ground"/chassis.  Finally, 
most amateurs do not ground their computers other than any 
chance grounds through common leads to their radio and/or 
the line "safety ground."  

The issues with both "radiated noise" related to USB and 
data loss in the presence of RF can be related directly 
to Pin 1 problems in the computer - laptops are more of a 
problem that old style metal case "tower" systems.  

The solution is multi-fold ... proper design of the computer 
motherboard AND chassis, proper grounding of the computer 
(a short strap to the station "common point ground") and 
eliminating common mode currents on cables coming into the 
shack (e.g., proper grounding of all cables to the common 
point ground at the entry window with common mode chokes 
between the entry window and equipment). 

73, 

   ... Joe Subich, W4TV 
       microHAM America 
       http://www.microHAM-USA.com 
       http://groups.yahoo.com/group/microHAM 
       support at microham.com 
 

 



> -----Original Message-----
> From: writelog-bounces at contesting.com 
> [mailto:writelog-bounces at contesting.com] On Behalf Of Jim Brown
> Sent: Thursday, November 08, 2007 11:08 AM
> To: WriteLog Reflector
> Subject: Re: [WriteLog] RFI and Keyers
> 
> 
> On Tue, 6 Nov 2007 20:49:42 -0500, Joe Subich, W4TV wrote:
> 
> >With respect, the microHAM products were done correctly with 
> >regard to any "pin 1 problem."  
> 
> While I respect Joe and his business, I believe that Joe is mistaken 
> about this. He and I are corresponding privately, and I've pointed 
> out some components of the RFI problem that others are seeing. I've 
> also seen a number of posts on the NCCC list from good engineers who 
> have fixed stability problems with Microham products using ferrite 
> chokes on interconnect wiring. That fix would not work (or be 
> necessary) if he was right. 
> 
> 73,
> 
> Jim K9YC
> 
> 
> 
> 
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