A "new" idea for RFI reduction:

Since we are getting a new roof installed I removed
all of my antennas. There has been a slight delay,
so I installed a temporary antenna and was disappointed
at the high level of RF noise.

"Common mode" RF noise is my biggest noise issue.
W1HIS's ground breaking "Common Mode Chokes"
goes a long way toward getting rid of this noise.

At my location there are two stage RFI filters on all the
"in house" low current RF noise sources. The higher
current RF noise sources have single stage RFI filters.

The incoming AC mains power is bypassed with
parallel 0.01uF and 0.001uF(1000pF) 2KV low
inductance capacitor. We also have a "whole house"
over voltage clamp at the breaker panel.

Every light switch has a 0.001uF cap across the
contacts.

For the most part devices in our home have been
chosen for minimum RF noise generation.

The telephone line, non DSL, has a common mode and
differential filter and over voltage protection immediately
after the NID. NID "Network Interface Device", AKA
"Demarcation Point".

My ground is much better then the typical ham or SWL.
I have a 3/8" copper tubing buried ~2' and bonded to the
utility (AC mains and telephone) ground. All of the antenna
masts have their individual ground rod and are bonded to
the utility ground.

In spite of all of these steps, I still have residual common
mode noise. This is made much worse by the temporary
antenna I amusing. To verify the noise was in fact common
mode, I turned off the AC at the meter base and disconnected
the telephone line at the NID.

I removed every battery from every smoke alarm, alarm clock
backup. So my home was "disconnected" from the world. And
my noise level was much lower.

My test receiver was a R2000 with a gel-cell providing operating
power. There were no other devices in the home powered up.

I did this on an afternoon when the power company was
scheduled to change our power transformer.

I was monitoring when they disconnected the transformer.
And other then a short nasty "buzz", there was almost no
effect on my received noise level.

So most of my noise was still self generated.

Bummer!

Will gave me a 250W Topaz "Ultra-Isolation" AC transformer that
has less then 0.005pF capacitive coupling between the AC mains
input output. I can not verify this because I can not measure
capacitor values below 1pF.

At 30 MHz the 0.005pF has a capacitive reactance of 1061033 Ohms.
This is over 1 million ohms. At lower frequencies this values
increases.
Any common mode noise coming through the transformer will have a
1M resistor in series.

Since my entire SWL setup draws less then 250W, more like 10W,
I decided to try the Topaz and lift the ground.

The NEC treats transformer as separately derived power. This means
I could lift the common ground and connect the neutral and ground
at the output of the transformer. And connect the new "ground" with
my house ground.

The house ground was not continued through to my room
ground.

I retested after the power and telephone connections were restored
and was surprised to find the RF back ground noise was almost as
low as when the power was disconnected.

I intend to do some additional tests when the roofers are done and I
am
using my normal SW antennas.


This week end I will be testing this at a friend's house who has a
more
"standard" ground situation. He has a modern home, 2005, with 2
ground rods, per NEC requirments , DSL, Cable TV and isn't the
slightest
interested in SWL. I know from prior experience his home is a
common
mode RFI noise hell hole. It will be interesting to see what, if any,
change
the Topaz will make.

Please note that Topaz Ultra Isolation transformers are expensive.
Standard isolation transformer will not provide this level of RF
common
mode noise isolation.

Terry

On May 23, 6:26 am, wrote:
The burried 5/8' copper tubing circles our entire home.
The 4 corners all have 8' grounding rods.

All connections to the ground ring are Calwelded.

This is a suplamental to the required NEC ground.

The utility has the required 28' grounding rods.

The entry point for antennas and the mast for VHF/UHF
disk cone has a 8' ground rod and this is bonded
to the ground ring and the utility grounding rods per
the NEC.

The Dallas Lankford "15' Relay Switched antenna"s
each have their own 8' grounding rod, but becuase
there is no direct connection to the house ground
system. By "no direct connection", I mean the
secondary of the transformer is isolated with no
connection to the primary.

I changed "ground rods" to "grounding rods" at the
request of our commercial electrician.

Terry

Jesus H. Christ Terry, if I had to do all of this to keep my noise low
I'd probably give up radio! I used to work with the guy who
originally designed the Topaz high isolation xfmr. He's older then I
am (ancient!) but an expert on this stuff. I t doesn't surprise me
because I think most of the noise that gets to the radio is carried on
the AC line, either as common mode or in some cases differential mode.

Frank
K3YAZ

In article . com,
wrote:


The incoming AC mains power is bypassed with
parallel 0.01uF and 0.001uF(1000pF) 2KV low
inductance capacitor. We also have a "whole house"
over voltage clamp at the breaker panel.

Every light switch has a 0.001uF cap across the
contacts.

Snip

You should only use specially rated capacitors for this type of
application. You understand that a capacitor on the mains supply draws
current to heat the dielectric as a consequence right?

You should also have a fuse of circuit breaker between it and the mains
supply in case it shorts. The lamp cord is not rated to what the house
circuit breaker rated at of course.

Here is the skinny on the subject.
http://my.execpc.com/~endlr/line-filter.html

He also describes a snubber network, a series resistor and capacitor
that is a good way of suppressing switch noise from rectifying diodes in
power supplies. The diode switch noise on power supply DC outputs causes
the hum on portable radios.

--
Telamon
Ventura, California

In article . com,
wrote:

On May 23, 10:03 pm, "
wrote:
On May 23, 6:26 am, wrote:



The burried 5/8' copper tubing circles our entire home.
The 4 corners all have 8' grounding rods.

All connections to the ground ring are Calwelded.

This is a suplamental to the required NEC ground.

The utility has the required 28' grounding rods.

The entry point for antennas and the mast for VHF/UHF
disk cone has a 8' ground rod and this is bonded
to the ground ring and the utility grounding rods per
the NEC.

The Dallas Lankford "15' Relay Switched antenna"s
each have their own 8' grounding rod, but becuase
there is no direct connection to the house ground
system. By "no direct connection", I mean the
secondary of the transformer is isolated with no
connection to the primary.

I changed "ground rods" to "grounding rods" at the
request of our commercial electrician.


Jesus H. Christ Terry, if I had to do all of this to keep my noise low
I'd probably give up radio! I used to work with the guy who
originally designed the Topaz high isolation xfmr. He's older then I
am (ancient!) but an expert on this stuff. I t doesn't surprise me
because I think most of the noise that gets to the radio is carried on
the AC line, either as common mode or in some cases differential mode.


Hey, if I had any sense I wouldn't be listening to SW in the first
place!

I got the idea to use the Topaz as an "ultra-isolation" transformer
from an experiment here atr work.

Snip

I've used them for low noise Faraday cage work. You have to filter all
lines in and out of the cage.

--
Telamon
Ventura, California

On May 26, 7:27 pm, Telamon
wrote:
In article . com,

wrote:

The incoming AC mains power is bypassed with
parallel 0.01uF and 0.001uF(1000pF) 2KV low
inductance capacitor. We also have a "whole house"
over voltage clamp at the breaker panel.

Every light switch has a 0.001uF cap across the
contacts.

Snip

You should only use specially rated capacitors for this type of
application. You understand that a capacitor on the mains supply draws
current to heat the dielectric as a consequence right?

You should also have a fuse of circuit breaker between it and the mains
supply in case it shorts. The lamp cord is not rated to what the house
circuit breaker rated at of course.

Here is the skinny on the subject.
http://my.execpc.com/~endlr/line-filter.html

He also describes a snubber network, a series resistor and capacitor
that is a good way of suppressing switch noise from rectifying diodes in
power supplies. The diode switch noise on power supply DC outputs causes
the hum on portable radios.

--
Telamon
Ventura, California

The caps in the breaker box have 1A fuses in series for protection.

The caps in the light switches have 10 ohm, 1/10W, metal film
resistors.

And yea I used the correct caps, I would hate to burn our home down.
My wife would be mildly miffed.

I am writing up a piece discribing my experiences at home and at
another house
detailing the positive effects the Topaz ultra-isolation. It is too
bad there is no
simple way to build broad band RF isolation transformers with less
then .5pF
capacitance between the primary and secondary.

Isolation of at least 10K is needed to knock common mode RFI down low
enough
to not be a problem. The trouble wil going with series inductance on
the shield, or
even harder, balanced feedline is the interwinding capactance allows
the noise to
sneak past.

Terry

Terry