[Elecraft] USB/RS-232 Cable

[Bob McGraw K4TAX]

I get some noise via that K3S to USB computer connection.  I applied a 
ferrite bead, about 1" long, so that the cable actually makes a 1 turn 
loop at each end.  This is one of the snap on beads.    Cured the 
problem and a couple of others.

The 120 Hz signal somewhat indicates a "ground loop" exists in the 
system.  {What ever a ground loop is.}  Make sure every piece op 
equipment is bonded to a common point, usually the station power supply.

If you are using an Astron linear supply, the 3rd pin ground connection 
may have failed.  I've repaired several of these units where the 3rd pin 
ground wire lug inside the supply was nicely insulated from the case by 
their wonderful paint job.  Correction requires opening the PS, removing 
the lug and screw, scraping away some paint and then put it all back 
together.

73

Bob, K4TAX


On 12/16/2017 10:34 AM, JJ wrote:
> I have a K3 and use a SDRPlay RSP1 as a panadapter.  Last night I noticed a
> huge jump in noise and then noticed a strong, wide, cruddy signal every
> 120hz which would indicate a power supply problem.  This problem is new.  I
> have been using this cable for a few years with no problems.  I do not know
> the cable's provenance .
> I finally traced the source of the noise to my K3 USB to RS-232 computer
> connection.
> When I disconnect the cable from the K3 the noise disappeared.  The noise
> only occurs when the cable is activated.  If turn on the K3 and start
> whatever SDR program there is no noise.  As soon as I activate the
> connection between the K3 and my computer with OmniRig the noise starts.
> The cable appears to otherwise be OK in it's operation.
> I don't have another cable to test to see if it is the cable or not so I am
> going to order another.
> Has anyone else ever experienced this problem?  I'm hoping it's not the K3
> Thanks,
> Jon WS1K
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