[Elecraft] serial interface noise on 160m -- propagates through K3 to coax cables and grounds...

[Mitch Mitchell]

Thanks to everyone who responded -- as far as directional antennas go the VX-3R yahoo group pointed out that the hand held has a fairly directional AM antenna that can be use to chase down noise.

I have been able to narrow the source of the noise down to the USB to Serial converters or the USB Hubs themselves.  The noise is getting into the ground through the serial interface on the K3 and then out to the coax shields.  I'll have to move a heavy desk to determine which of the two potential offenders is actually generating the noise.

I was curious if anyone else had experienced this with a K3 and USB<->Serial converters -- the pulsing of the noise turns out to be HRD polling the K3 for VFO position -- once every 300ms -- and when I turn off polling the noise stabilizes but is still present.  I am doing research to see what I can do to eliminate it.

While chasing this down with my HT,  I found several other sources of noise -- all within my shack, so I have a noise eradication project to embark on now.

73,
Mitch Mitchell, AE5HO
mitchmitchell1616 at msn.com




From: Leigh L. Klotz, Jr WA5ZNU 
Sent: Monday, June 22, 2009 12:59 AM
To: elecraft at mailman.qth.net 
Cc: Mitch Mitchell ; Ken Kopp 
Subject: Re: [Elecraft] serial interface noise on 160m -- propagates through K3 to coax cables and grounds...


Ken K0PP has pointed out I said it all wrong.  With my poor choice of the terms I have confused even myself, and produced gibberish.
I'll quote Ken because he said it clearly:


  Loops, if built correctly, have a NULL in both broadside directions ... through the hole in the loop, so-to-speak.

  The nulls are -very- narrow, but deep and are essentially the only directivity exhibited by a loop.

I've successfully used the cardboard/test-lead loop antenna and TH-F6A HT I described to locate noise coming from a switching power supply for a lamp in a neighbors house, the charger on my robot vacuum cleaner (a menace surely no 1950's ham ever faced), a laptop power supply, and a home music player power supply.  Turning off the house breakers is a great first step to tell you what room it's in, but if you already know it's coming from the shack, the small loop helps a lot.

Leigh/WA5ZNU


  Mitch, 
  You may be doing this already, but you can make a small loop antenna for your HT (TH-F6A?) to DF the noise. 
  A really simple one is just a short SMA to BNC jumper with a square wire loop (alligator test leads?) taped to a piece of cardboard. 
  When the loop is broadside to the noise, it will be the loudest, and when parallel, the null will be sharpest. 
  This type of antenna is inefficient, and so it work well to DF noise sources to a few inches. 
  So you can tell where noise is being radiated inside your shack.  (It might be created in one spot and radiated elsewhere, of course.) 

  If you need a better DF antenna for RFI, make a better version that is shielded, by using a piece of scrap coax: 
  http://lists.contesting.com/_rfi/2005-01/msg00078.html 

  Leigh/WA5ZNU 

    Hello, 
    I have been hearing an annoying noise on 160m that has a pulse rate of about 1/3 of a second.   After observing the behavior when I do certain things with my K3 and my computer I found that the source of the pulsing is Ham Radio Deluxe polling the K3 for VFO changes -- it polls every 300ms.  However, when HRD is shut down (no other serial port activity) the noise is still present as a constant tone with no pulsing effect.  My first suspicion is the USB to Serial adapters on the computer, but I am also thinking that maybe the noise is coming from the USB hubs or their wall warts.  I can hear the noise on the K3, my winradio, and my handheld (which is picking up the noise on 80m).  I was wondering if anyone has seen something like this and whether this might be coming from inside the computer or the USB hubs.  I am going to pull out my desk from the wall and start tracking this down to the source but I wanted to see if anyone else had experience with this sort of thing and any  thoughts or recommendations? 

    Best Regards, 

    Mitch Mitchell 
    AE5HO 
    mitchmitchell1616 at msn.com