Better 'grounding' ... I like.
It means even greater "displacement currents" are induced in equipment when
said equipment is in the high-intensity E-field of the antenna (maybe twenty or
thirty feet from the end of a 160m meter dipole or inverted V.
(Remember, invoking the reciprocity theorem means that currents can be induced
back into the antenna which affects the receiver by locating little noisy
voltage sources in the antenna's E-field pattern as well.)
As a user of moderate-sized tuned QW loops, I find less of a problem with RFI
(rx and tx) even operating 20 feet away (at ground level) from the antenna at
the 1 kW power level.
SO, the point of this discourse is, take a few moments to envision where your
gear is located in relation to the High E fields of the antenna. Again, this is
important on RX in the reverse direction.
73, Jim WB5WPA
From: Gary Smith via RFI <rfi@contesting.com>
To: rfi@contesting.com
Sent: Monday, March 13, 2017 11:38 AM
Subject: Re: [RFI] USB qrm - what to do?
How is your station grounded? Trusting the old "attach it to the water
pipe, that'll be fine"? Sounds like ground looping to me.
Most ground looping problems, to me this is what your describing, can be
cured by going back to the basics. That is, a 6 or 8 foot ground rod
driven into the dirt (ground) nearest your shack. If you can't find or
don't want to spend the bux for 1.5 wide copper strapping, take a old
piece of coax, marry the center conductor to the shield, then rung it
into the shack. Hook each piece of equipment to the coax, (don't series
them) see if that doens' help reduce the noise level. Sounds as if you
have lots of little antennas looking for any signal of any kind, and,
finding quite a few.
Gary...wa6fgi
On 3/13/2017 7:48 AM, Robert Nobis wrote:
> Pete,
>
> Besides using quality shielded USB cables, make sure that your computer is
> also separately grounded to your common station ground with a one inch ground
> strap. In other words don’t rely on the ground pin of the AC power line.
>
> 73,
>
>
> Bob Nobis
> n7rjn@nobis.net
>
>
>> On Mar 13, 2017, at 04:31, Pete Smith N4ZR <n4zr@comcast.net> wrote:
>>
>> My shack computer has 6 different USB devices attached. When I disconnect
>> all but the keyboard, it cuts the background noise level on 160M by a
>> whopping 25 dB, from S9+18 down to S8 (as monitored by HDSDR and my QS1R,
>> calibrated by an Elecraft XG3).
>>
>> What is to be done? It doesn't seemvery feasible to wind each usb cable on
>> a small type 31 toroid and get enough attenuation . Available snap-ons all
>> seem to roll off dramatically below 25 MHz. Can a common mode filter be
>> built using discrete components that will have decent attenuation at 160 M?
>> Or, maybe, is such a filter available commercially? I have Googled and
>> reviewed K9YC's tutorial but found nothing directly apposite.
>>
>> Thanks for any ideas!
>>
>>
>> --
>>
>> 73, Pete N4ZR
>> Check out the Reverse Beacon Network
>> at <http://reversebeacon.net>, now
>> spotting RTTY activity worldwide.
>> For spots, please use your favorite
>> "retail" DX cluster.
>>
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>>
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