Kelly Johnson n6kj.kelly at gmail.com
Mon Jan 28 19:46:22 EST 2008

Did I not say "antenna system" in my original post?  Why yes, I did.
What was I referring to?  All the same things you mentioned like
transmission lines which allow RF to travel back into the shack on the
shield OR systems with part of the antenna inside the house (like long
wires with the tuner in the house).  We're saying the same thing.  I
just said it with fewer words :-)

On 1/28/08, Jim Brown <jim at audiosystemsgroup.com> wrote:
> On Mon, 28 Jan 2008 15:59:51 -0800, Kelly Johnson wrote:
> >If, on the other hand, you find TVI on multiple
> >TVs then I would suspect a poorly designed antenna system which is
> >allowing RF into the house.
> Well, sort of. But ANY antenna that is WORKING is going to put RF in
> your house. A better way to look at it is to say that some antenna
> SYSTEMS inherently put more RF there than others. :)  The word
> "systems" is quite important.
> If your antenna is something like a beam or dipole, most of the RF is
> radiated by that beam or dipole -- that is, the active elements are
> "up in the air." Their feedline WILL, however, become part of the
> antenna if it is not fully decoupled by a REALLY good choke (often
> called a balun). See my tutorial for more of that.
> If what you CALL your antenna is ANY form of wire that ends in your
> shack, everything connected to the chassis of your rig is also part
> of the antenna system. This includes the power system safety ground
> (and all of the wires connected to power system ground throughout
> your house), whatever you CALL ground (the wire going to a rod,
> radials, etc), and anything CONNECTED to the power system ground. All
> of that wire that we like to call "ground" IS PART OF THIS KIND OF
> ANTENNA, and the RF current that it carries is a MAJOR contributor to
> RFI, TVI, etc.
> This current causes problems three ways. First, the wires carrying
> the RF current (your transmitter power) will RADIATE that RF, just
> like any other antenna. Second, that current can flow INTO EQUIPMENT
> that has pin 1 problems!  Third, that current causes IR drop in the
> shields of coax that carry it, and that RF is added to the signal on
> that coax. The latter mechanism is most likely to be a problem on
> coax with thin foil/drain shields (like MATV cable) and low HF band
> operation.
> See my tutorial for a discussion of pin 1 problems. They are the #1
> cause of RFI!  Lousy shielding of the equipment itself is another
> biggie -- that's the likely cause of the problems that the RIGHT
> ferrite choke won't fix (like what Kelly is talking about).
> http://audiosystemsgroup.com/RFI-Ham.pdf
> It's too easy (and overly simplistic) to blame a bad antenna for RFI.
> Those of us who live on small lots MUST use less than ideal antenna
> systems if we want to work the lower HF bands [somebody tell me how I
> can put a 160M antenna on a 100 ft x 40 ft lot without end-feeding
> some sort of wire that ends at or near the transmitter], and even our
> very  good tribander at 40 ft (or even 70 ft) is going to put a lot
> of RF onto the wiring of the home entertainment rigs of you and your
> closest neighbors. If we want to operate without RFI, we've got to
> learn to blame (and fix) the real causes -- the pin 1 problems, lousy
> coaxial cables, and lousy shielding in that home equipment, not our
> antennas!
> FWIW -- I ran 1kW from a wood frame 2-flat on a 135x40 ft lot in
> Chicago on 160-10 and 100W 50-440 MHz. The only RFI issues I couldn't
> fix were cheap office phones (mostly a problem on 6M, not HF) and a
> toy musical instrument in my tenant's apartment. And I never had a
> complaint from a neighbor, even from houses only 25 ft either side of
> mine!
> http://audiosystemsgroup.com/K9YC/k9ycant.htm
> 73,
> Jim Brown K9YC
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