Radiation from the feedline is usually the least of one's problems.

99 % of RFI is due to radiation from the very nearby antenna.

==========================================

Reg Edwards wrote:
Radiation from the feedline is usually the least of one's problems.

99 % of RFI is due to radiation from the very nearby antenna.


That's rubbish - have you ever *measured* the RF currents in your
station wiring?

....no, I thought not.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

"Ian White GM3SEK" wrote
Reg Edwards wrote:
Radiation from the feedline is usually the least of one's problems.

99 % of RFI is due to radiation from the very nearby antenna.


That's rubbish - have you ever *measured* the RF currents in your
station wiring?

==========================================

No, but I HAVE measured RF current in the antenna - from where most
RFI originates.

Have you ever run 400 watts from an 80 meter 1/2-wave dipole a few
feet above your roof and not far from the TV aerial?
----
Reg.

Reg Edwards wrote:

"Ian White GM3SEK" wrote
Reg Edwards wrote:
Radiation from the feedline is usually the least of one's problems.

99 % of RFI is due to radiation from the very nearby antenna.


That's rubbish - have you ever *measured* the RF currents in your
station wiring?

==========================================

No, but I HAVE measured RF current in the antenna - from where most
RFI originates.

Can't you see the circularity of your own 'logic'? If you haven't
measured common-mode RF current in the feedline as well, you don't
actually have a clue where the interference is originating. All you have
is an unsubstantiated opinion.


Have you ever run 400 watts from an 80 meter 1/2-wave dipole a few
feet above your roof and not far from the TV aerial?

I'm not disputing that RFI very often originates from the antenna - of
course it does (and the question you pose is a set-up, designed to make
*sure* it does).

What I object to is your sweeping generalization that "99 % of RFI is
due to radiation from the very nearby antenna." When absolute nonsense
is delivered with absolute confidence, some unfortunate beginner might
actually believe it.

However, since you asked...

In a typical small British back garden, I have been forced to do
something very similar to what you describe. Sure enough, it caused RFI,
but the interference was *not* due to my antenna! It was entirely
mains-borne, and only to the two neighbours (not the closest) who were
connected to the same phase as ourselves. The cause of the interference
was that a substantial fraction of my RF ground current was going into
the mains ground. Once I'd cleaned up my act and stopped injecting RF
current into the mains, the interference stopped too.

The high field strength from my antenna wasn't a problem at all, and the
neighbours continued to watch their TVs until I took the antenna down.

That's how it was in that one particular case.... but unlike you, I'm
not claiming it represents 99% of anything.

With RFI, the only safe generalization is to keep your mind open to
*all* possibilities.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Tue, 3 Jan 2006 14:44:01 +0000, Ian White GM3SEK
wrote:

Can't you see the circularity of your own 'logic'? If you haven't
measured common-mode RF current in the feedline as well, you don't
actually have a clue where the interference is originating. All you have
is an unsubstantiated opinion.

Ian, Ian you should know by now you're dealing with the "Prince of
Factoids".

Danny, K6MHE




email: k6mheatarrldotnet
http://www.k6mhe.com/

That's an interesting statistic. How did you arrive at it?

Roy Lewallen, W7EL

Reg Edwards wrote:
Radiation from the feedline is usually the least of one's problems.

99 % of RFI is due to radiation from the very nearby antenna.

==========================================

Roy!

Just a legitimate crude guess - perhaps biassed a little in the
opposite direction to the normal excessive bias.

If I remember correctly, you, your very good self, used Eznec to
demonstrate that even under the most adverse worst-case conditions you
could think of, power radiated from the feedline is only a fraction of
that radiated from the antenna.

.. . . . . and the equipment being interfered with is in the
near-field of the antenna just as it is in the near-field of the
feedline. That, for most people, includes your next-door neighbors.
Especially if your next-door neighbors happen to be within the antenna
beam.
----
Reg.

============================================

"Roy Lewallen" wrote
That's an interesting statistic. How did you arrive at it?

Roy Lewallen, W7EL

Reg Edwards wrote:
Radiation from the feedline is usually the least of one's
problems.

99 % of RFI is due to radiation from the very nearby antenna.

Reg, it would really be nice if you could come up with some new topics
to keep you entertained on those dull evenings. You brought that one up
just four months ago. Maybe you can keep a list of your favorites,
noting when you used each one the last time, and giving us a little
longer break between repetitions.

Reg Edwards wrote:
Roy!

Just a legitimate crude guess - perhaps biassed a little in the
opposite direction to the normal excessive bias.

If I remember correctly, you, your very good self, used Eznec to
demonstrate that even under the most adverse worst-case conditions you
could think of, power radiated from the feedline is only a fraction of
that radiated from the antenna.

Sorry, you don't remember correctly. I said on quite a number of
occasions (and you once even agreed) that you can't assign radiated
powers from different parts of an antenna system. It was actually kind
of sad -- you kept loudly demanding that I provide fractions of power
from the feedline and antenna, ignoring my statements that it couldn't
be apportioned that way, and some time later you said out of the blue
that it couldn't. And then you wrote a program that does just that. At
the end of this posting is a summary of your contradictory statements
which I originally posted here on Sept. 1.

I did find with EZNEC that the current on a feedline could be very much
larger than your program predicts.

. . . . . and the equipment being interfered with is in the
near-field of the antenna just as it is in the near-field of the
feedline. That, for most people, includes your next-door neighbors.
Especially if your next-door neighbors happen to be within the antenna
beam.

Depends on the orientation of your antenna and the size of your lot. My
antennas are some distance from the house, but the feedlines come right
inside.

----- My posting on this group on 9-1-2005 -----

If anyone besides me is having trouble keeping track of what Reg is
trying to say, maybe the following recent quotes will help. That is,
they'll help you understand why you're having trouble keeping track.

For what it's worth, I agree with the first quotation of 8/31. But
apparently Reg doesn't, even though he said it.

Roy Lewallen, W7EL

8/30:

Perhaps somebody might be prepared to state the power actually
radiated from feedlines in watts. At least it may create the
impression you know what you are talking about.

8/30:

Roy, do everybody a favour, by stating, numerically, how much power is
radiated from feedlines. Then somebody might have some confidence in
what you are bafflegabbing about.

8/31:

Any current which finds its way on to (3), which ought to flow in the
antenna, will result in the coax participating in the radiation
pattern of the whole antenna structure.

BUT IT IS A SILLY QUESTION TO ASK HOW MANY WATTS ARE RADIATED FROM THE
FEEDLINE.

OR, CONVERSELY, HOW MANY MICROWATTS ARE PICKED UP BY THE FEEDLINE ON
RECEIVE.

The feedline cannot be treated in isolation as if it behaves
independently of the antenna. For starters, the radiation resistances
of the feedline and antenna do not add arithmetically. They interact
with each other.

8/31:

If you erect a 10 meter 1/2-wave dipole and center-feed it with a 50
feet length of coax, and then transmit on 1.9 MHz, 99.9 percent of
available power will be radiated from the feedline and only 0.1
percent from the antenna itself.

http://www.smeter.net/feeding/feedpowr.php:

Centre-Fed Dipole - Radiation from Coaxial Feedline
Author: R.J.Edwards G4FGQ © 25th March 2003

Program Notes
.. . .
With no loss in accuracy, to simplify the model, the transmitter is
located at the dipole centre and the coaxial line is replaced by a
single conductor of the same diameter as the coaxial braid. There are 3
radiating elements. Radiation resistance, input impedance, and input
current of each element is calculated. Finally, the percent of total
power radiated by each of the three elements is calculated.

---------------------

Roy Lewallen, W7EL

Reg Edwards wrote:
Radiation from the feedline is usually the least of one's problems.

99 % of RFI is due to radiation from the very nearby antenna.

In some cases, that nearby antenna is a counterpoise
laid across the floor which some people consider to
be a "ground" of sorts. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Reg Edwards wrote:
Radiation from the feedline is usually the least of one's problems.

99 % of RFI is due to radiation from the very nearby antenna.

==========================================


REALLY??

I thought most RFI issues, in today's world, are related to lack of
selectivity in the device experiencing the interference. RFI is
generally a susceptibility in the interefered with device. Read ALL the
information provided and you should find a manufacturer's disclaimer.

If the transmitted signal is 'clean' [meets applicable standards] then
the cause of RFI is SUSCEPTIBILITY in devices designed for MAXIMUM profit.

I'm not responsible for susceptibility issues. A neighbor complained
that my station was coming through his computer speakers. I invited him
to my station and turned on my computer and speakers. At 1 KW output
there was/is no RFI in my speakers !!! [My computer is co-located with
my station]. I suggested that he contact the manufacturer of the
speakers and obtain information to reduce susceptibility. I showed him
how I solved the susceptibility issue for my computer. The
responsibility is now his.