[Elecraft] RFI resistant Monitor

[Myron Schaffer]

One thing I have noticed over the years is that the near-field noise is present with most any modern electronics. The switching frequency is between 200-300kHz and can be easily sniffed with a pocket AM radio (harmonics of that fundamental switching frequency are easily spotted with an AM radio). When I bring my CCrane Pocket Radio in the near field at the operating position, I can’t tune in the semi-local 600 KCOL out of Greely, CO. If I back up a few feet the noise level drops considerably and the station is audible again. The CC Pocket Radio has a fairly good front end with somewhat good selectivity but is still overloaded with IBOC noise.

I have battery chargers, an old Dell 1501 laptop, an external HD with switcher, the list goes on. Common mode noise and strong near-field noise is the bane of my ham radio existence in this RFI rich environment. 

Myron WV0H
Printed on Recycled Data

From: Jim Brown
Sent: Monday, April 11, 2016 12:14 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] RFI resistant Monitor

On Sun,4/10/2016 10:44 PM, KC6CNN wrote:
> I just found that when the monitor is on it adds 2 bars of noise to my
> meter. It is also turning off when I operate on certain bands.

I had exactly that experience with a Samsung that W4UAT gave me because 
it did that in his shack too. It also makes RF noise. The good news is 
that not all Samsung monitors are RFI dogs. I have two recent model 
Samsungs in my house and four in the shack. They are designed to run on 
power supplies labeled 14VDC, and the supply they sell you is a 
switching power supply that makes RF noise. I throw those power supplies 
away, cut the attached power cable and attach red/black PowePoles, and 
run them from either the 12V battery system in my shack  or a small 12V 
lead-acid cell that I float-charge from a linear 12V wall wart.

I also use ferrite common mode chokes on both the video cable that runs 
to the computer and the power supply cable "just in case" some RF trash 
is conducted to those cables, which the cables could radiate.

All that, and a lot more, is discussed in this "in progress" article for 
the National Contest Journal.  k9yc.com/KillingReceiveNoise.pdf

73, Jim K9YC
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