A "new" technique for measuring differential mode to common conversion.
 

Regulars here may have followed my efforts to deal with noise
generated within
my own home. Along the way I read W1HIS's work on "Common Mode Noise"
and further study revealed differential noise becomes a problem when
it becomes
common mode noise.

W1HIS does a great job of describing how and where to use filters and
ferrite
to reduce noise from the home and to prevent noise from going up the
coax to
enter the antenna.

The exact method of DM conversion to CM has intrigued me. Reducing DM
is
the most useful tool for stopping self generated RFI. But you can't
get rid of all
of the DM noise. So I have been trying to decipher the riddle. I have
gathered a
lot of references and tried to develop a "ressonable" way to explain
the exact
conversion method.

In the process I have made a lot of measurements and wasn't have any
great
success at building a model to deal with this. My method of injecting
SM and
seeing where it becomes CM was useful but left gaps.

There are days I am so dense it amazes me I accomplish anything. A
net
search for another topic and found a article by Jasper Goebloed
entitled
"Reciprocity and EMC measurements".

It is so simple. Inject a Common Mode noise source and follow the
conversion to Differential Mode noise.
www.ieee.org/organizations/pubs/newsletters/emcs/summer03/jasper.pdf

This is a very useful tool that avoids the quasi legal use of my 10mW
3.58MHz,
80M ham band, RF source.

Assuming anyone else is trying to tame their self generated RFI is
interested,
this is a very useful method that allows us to inject CM noise, that
does not
radiate a significant amount of RF, IE I can't receive it 20' away
from the
power cable. I am using a home made ferrite toroid

Will will post this and the pdf in his stopRFI page in the near
future.

Terry

A "new" technique for measuring differential mode to common conversion.
 

In article .com,
wrote:

On Oct 10, 2:17 am, "Al" wrote:
wrote in message

oups.com...

Regulars here may have followed my efforts to deal with noise
generated within
my own home.
Terry

Your posts on this subject and others similar to it have been excellent. I,
and I'm sure others, appreciate the time and work you put into these
subjects and for making this information available.

Thank you.

Al KA5JGV
San Antonio, TX

Thanks, there are days I feel like a lone voice in the woods.

very grateful to read your posts. Look forward to your future articles.
-j

A "new" technique for measuring differential mode to common conversion.
 

Thank You Terry!

Burr

A "new" technique for measuring differential mode to common conversion.
 

On Oct 9, 10:25 pm, wrote:
On Oct 10, 2:17 am, "Al" wrote:





wrote in message

roups.com...

Regulars here may have followed my efforts to deal with noise
generated within
my own home.
Terry

Your posts on this subject and others similar to it have been excellent. I,
and I'm sure others, appreciate the time and work you put into these
subjects and for making this information available.

Thank you.

Al KA5JGV
San Antonio, TX

I also want to say thank you for all your effort and the sharing of
this information. I think a low RF noise enviornment is more
important than the receiver used, much like a poor antenna will make a
$2000 radio perform almost no better than a $200 one.

A "new" technique for measuring differential mode to common conversion.
 

On Oct 11, 12:59 am, wrote:
On Oct 9, 10:25 pm, wrote:



On Oct 10, 2:17 am, "Al" wrote:

wrote in message

roups.com...

Regulars here may have followed my efforts to deal with noise
generated within
my own home.
Terry

Your posts on this subject and others similar to it have been excellent. I,
and I'm sure others, appreciate the time and work you put into these
subjects and for making this information available.

Thank you.

Al KA5JGV
San Antonio, TX

I also want to say thank you for all your effort and the sharing of
this information. I think a low RF noise enviornment is more
important than the receiver used, much like a poor antenna will make a
$2000 radio perform almost no better than a $200 one.

For a little over a year I had an AOR7030+ to store for a friend.
A great receiver with a great selection of filters, but a PITA menu
system.
I also own a R390 and had a Drake R8B for a few months.

At my location, even after all my noise mitigation efforts, the 3
great receivers
were not significantly better at digging out the weak one. True the
filters and
superior front end, lower phase noise and better detectors made
listening
a lot easier and more fun, but at the end of the day my R2000 could
hear
better then99% of what the other three could.

Even my lowly DX398 could hear about 95% of what the best could.

Don't get me wrong, as soon as I can I will upgrade to a R8B and with
luck
a 7030+. SDR's are improving so fast that may divert me, but I think I
will
stick with conventional for a while longer.

The R2000 is rated by Sherwood labs as having ~-127dBm sensitivity.
The best I have seen the noise floor around here was during an ice
storm 14 years ago when I had 2 days of SW bliss. The noise floor
was around -110. So even then I had 17 dB of gain that I couldn't use.

Of course the better radios are much better at picking one signal in
a
crowded situation. The R2000 suffers from pretty poor close signal
separation. For 2 signals of roughly the same strength it isn't an
issue,
but when the unwanted signal is more then about 3 times strong as
the desired signal, the R2000 has very tough time picking it out.

The R8B and 7020+ are great. The R390 is better. But the R390 is no
fun to rapidly tune from one frequency to a very different frequency
in
a hurry.

Terry