"Key word, Balanced, done, if you keep it balanced it is self shielding,
if it gets un balanced then signals leak out and in."
Sounds good, but not possible in the real world. Small changes in balance
mean big dB changes. It's easier to achieve balance on transmit than
receive assuming the line is not coupled to nearby objects. On receive,
noise sources can arrive anywhere from 360 degree spherical directions.
While the line may achieve good rejection when the noise is perfectly
broadside to the line, the line will not maintain that balance if the noise
source moves say...90-degrees away. Just try and cancel noise from
multiple noise sources like a linear compressor from the kitchen
refrigerator in this direction, the direct-drive washing machine from that
direction, and the nearby shack switching power supply from another
direction.
You still have not indicated HOW you achieve balance. We all know balance
is needed. Tell us exactly how you do it and check for it and ensure
balance exists across the bands of operation.
Paul
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Paul Christensen
Sent: Thursday, August 04, 2016 9:51 AM
To: rfi@contesting.com
Subject: [RFI] FW: Quiet Switching Power Supply?
>"Unless you're in a screen room or 100 miles from civilization, the
background noise is going to cover up any minuscule noise that the best
switchers for ham use are going to emit. "
Dale, that's probably true when using coaxial lines and resonant antennas
but all switching supplies emit RFI - some more or less than others.
When using open feeders that run across the length of a home, any small
amount of RFI can be detected, including RFI emitted from the best ham
switching supplies. On receive, balanced feeders cannot cancel all noise
sources, since the arrival angle to the line is inconsistent.
Trans-positioning the line may sometimes help.
At my home QTH, coax is run through the house to feed a motorized,
symmetrical balanced tuner that's located outside and away from home RFI
sources. Problem solved but it requires an extra level of cost and
complexity.
Just my opinion, but for ladder line/open feeder runs through a house or
apartment, I would stick with linear supplies and linear wall-warts for
accessories.
Paul, W9AC
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