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