[Elecraft] Noise with KUSB

[Joe Subich, W4TV]

> On Tue, Aug 4, 2009 at 6:38 AM, Svend Spanget 
> <spanget at privat.dk> wrote:
> 
> > I recently discovered the source of a very annoying noise in my K3. 
> > When unplugging the USB cable from my USB hub the noise in the 
> > receiver disappears. How do I get rid of this? I am using HRD, so a 
> > connection to my PC is really needed...
> > 73's Svend, OZ7UV


One of the most common sources of USB device related noise is 
a bad/open shield on the USB cable.  First thing to try is a 
different USB cable.  Since you have a hub involved, don't 
forget to check the cable between the computer and the hub as 
well as the power supply for the hub.  Also make sure the 
computer is properly grounded to the station's common ground 
point and the shield has a good contact to the motherboard 
groundplane and the chassis. 

If the noise is from the RS-232 side of the USB to RS-232 
converter, place a jumper across the RF choke in pin 5 of 
the RS-232 connector (Elecraft RF Immunity Mod -
<www.elecraft.com/K3/mods/ELECRAFT_Application_Note_Improving_the_Immunity_of_
the_Rear-Panel_KIO3_RS232_and_Audio_Connectors_to_RF.pdf>. 
In addition, consider making your own RS-232 cable using 
K9YC's suggestions (CAT5 cable with pins 2,3,4 & 7 each 
on a separate "pair" with the other wire of each pair 
connected to the shell of the connector).  The K9YC cable 
makes the RS-232 signals "balanced" and cancels any radiated 
noise using the "magic" of twisted pairs. 

73, 

   ... Joe, W4TV