On Jan 18, 4:23*pm, dave wrote:
On 01/18/2011 02:17 PM, D. Peter Maus 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.

You need to embrace ferrites. They're like putting a low pass filter is
series with your mains. Shunt caps are scary. MOVs, sure.

Thanks - Maybe, but I think ferrites on the RF cables might be more
critical than on the power cables. The radios are nice and quite when
I disconnect the antennae; no noise level at all even with the
multiple preamps all the way up.