On 1/18/11 21:59 , bpnjensen wrote:
On Jan 18, 2:17 pm, "D. Peter wrote:
On 1/18/11 16:05 , bpnjensen wrote:









On Jan 18, 10:57 am, John wrote:
On 1/18/2011 10:44 AM, bpnjensen wrote:

...
Actually, no, and I am sorry if there was a misunderstanding - I meant
an inline (in the coax) RFI reduction system.

Baluns/ununs really are NOT an RFI reduction system. They provide
proper impedance matching between antenna and feedline. Coax, with an
rf choke (can be a balun/unun) allows the feedline to run though noisy
areas and not pick up the noise there, such as when it enters a house
with noise present.

Baluns/ununs/rf-transformers, because of the use in gaining a superior
match (transfer of signal energy) improves signal to noise ratio, in
most instances, and this can appear to be functioning as a "RFI
reduction system."

Some useful links:http://users.belgacom.net/hamradio/s...ongwire%20Balu...

Regards,
JS

OK, understood, but I have always thought (based on what I have read)
that one of these matching transformers, properly deisgned and
grounded, can bleed off some noise to ground. Am I misled?

Local environmental noise, and static, yes. Man made noise, or
noise radiated into the antenna space, not so much, no.

A properly designed matching transformer will improve the
transfer of antenna output to the receiver. And it will help drain
off static buildup on the antenna, and help reduce the noise floor.
But, if noise is being radiated into the air, as from powerlines,
digital toys, and dimmers and similar sources, and your antenna is
picking that up, it will depend on the antenna's ability to
discriminate between desired and undesired frequencies whether or
not you see a reduction in undesired signals.

It sounds as though much of your noise problem is related to your
connection to the mains. Mains borne noise is a big problem in radio
hobbycraft. Most of the noise in my own area is brought in through
the mains. The remainder is radiated from the hundreds of devices
throughout the neighborhood.

It's possible, though a PITA to do so, to bypass the mains with
safety caps between .1 - .01mfd (safety caps are essential, here,
for fire prevention) to reduce the irregular impulses on the line.
And isolation transformer, balanced to ground will also produce
significant results in reducing your noise, but that can be expensive.

Your least difficult path may be in isolating your radios from
the mains, entirely, and move to battery power.

Thanks, Peter - This may be all true - but for the record, with the
radios plugged in, I disconnected the antennas and kept the grounds
connected. The radios got very quiet; based on this, I don't think
it's the mains.


I had a noise I couldn't get rid of, a few years ago. Everything
pointed to some radiated phenomenon. Tried disconnecting the antenna.
Things got very quiet. Finally tracked it down with a Zenith transistor
radio. It was, in fact, noise on the mains, radiated into the antenna
space. Filtered the line and modded an offending device that was putting
the spike on the line. Cleaned it right up.

A transitor radio can be useful in tracking down the source. Follow
the noise, turn off each implement one at a time, and you'll find the
source or sources of noise.

You sound like you're living in the noise equivalent of the Little
Big Horn.



FWIW, I have an RFI filter on the 115 VAC - this item:

ICE:

http://www.iceradioproducts.com/imag...ersarticle.pdf

The difference between using it and not using it is slight, but
noticeable.

Such a device is best used as close to the source as practical.