From: [email protected] ([email protected])
         Subject: Re: Tuneable antenna for 1610 KHz...an update 
         Date: 1999/03/18 

    I know that there are sources out there saying that the length of
    wire in a coil counts toward the antenna length as far as the FCC
    is concerned.  I suspect that you can even get that answer from
    some FCC staff members. What they don't realize is that the coil
    is just an inductor, not an antenna.  The current flows around
    and around the turns and certainly produces a magnetic field near
    the coil, but that magnetic field would have to have an
    accompanying electric field of the correct magnitude and phase
    for radiation to take place. The electric field doesn't develop
    to any significant degree; the magnetic field dies out very close
    to the coil. [A very small amount of radiation takes place along
    the length of the coil due to the axial component of current
    resulting from the pitch of the winding - it is reasonable, in my
    opinion, to include the length of the coil itself, not the wire
    in it, in the length of the antenna.]

    If someone, like an FCC employee, tells you that you have to
    count the length of wire in a loading coil in the antenna's
    length, here's a question to ask of them:  Why can't I connect my
    transmitter to a 200 foot tower through a capacitor since the
    wires in the capacitor don't touch - just take an ohmmeter and
    measure the capacitor and you can see that the wires don't touch?
    In other words, if an inductor isn't an inductor but is a wire
    instead, then a capacitor isn't a capacitor... it's just an
    insulator! That ought to blow their minds.

    By the way, the improvement to be had by installing an
    appropriate loading coil is enormous.  A 10 foot wire and simple
    ground connection probably present an impedance of a few ohms
    resistance with a few hundred ohms capacitive reactance at the
    antenna input, depending on the frequency in the AM band. 
    Cancelling the capacitive reactance can result in many times as
    much current flowing in the wire... with many times as much
    radiation.

    Ronald Rackley, P.E.
    Sarasota, Florida
    
    

         From: [email protected] ([email protected])
         Subject: Re: Tuneable antenna for 1610 KHz...an update 
         Date: 1999/03/24 

    I certainly don't want to give any advice that would get anyone
    in trouble with the FCC.  I just find the idea of having to
    include the wire of an inductor in an antenna's length to be
    absurd because an inductor is an inductor, not an antenna.  I
    gave a technical explanation of why in my earlier posting on the
    subject.

    Why don't you have to take the tuning inductor inside a phono
    oscillator apart and measure its wire?  How about those little
    toroids inside modern solid state units?  Using this logic,
    shouldn't you have to measure every inch of conductor from the
    tube or transistor that develops the RF power and include it in
    your antenna length?  What about coils that are wound on cores
    and use less wire to obtain the same amount of inductance -
    shouldn't you have to use an "equivalent" wire length to penalize
    yourself for cheating and using a core?

    It is true that an inductor is made of wire.  It is also true
    that a capacitor is made of insulating material.  The two are
    duals of each other as stored energy devices.  Their RF conducting
    properties are determined by the energy stored in the magnetic
    field surrounding the coil in the case of an inductor and in the
    electric field across the insulating material in the case of a
    capacitor.  

    If we are going to ignore the real function of a coil
    and view it as the wire used to make it instead, why can't we
    treat a capacitor the same way?  We would view it only as what it
    is made of, making it an insulator.  How about that?  Just put a
    capacitor in your wire 10 feet from your transmitter and then
    connect as much wire as you like - even hundreds of feet -
    without having it count because it is insulated from the antenna.
    NOTE: I'M NOT SUGGESTING THAT THIS SHOULD BE LEGAL - I'M MERELY
    TRYING TO ILLUSTRATE THE ABSURDITY OF HAVING TO COUNT THE
    STRECHED-OUT LENGTH OF WIRE IN AN INDUCTOR IN AN ANTENNA'S
    LENGTH.

    I'm not a neighborhood broadcaster.  I'm familiar with 100 mW
    "transmitters" because I have one that I couple into my antique
    radios so that I can listen to jazz and big band music on them. 
    If I wanted to be a neighborhood broadaster, I'd use a 10 foot
    wire with an appropriate loading coil and be prepared to "go to
    the mat" if the FCC says that I can't do that.  I know I'd win. 
    [If you don't want to "go to the mat" with the FCC, maybe you
    should play it safe and not use a loading coil.]

    Ronald Rackley
    Sarasota, Florida
    

 

And now another point of view from the Community Radio USA message board.

       Name: Jonathan Smick
       E-Mail: [email protected]
       Date: 12/4/02 10:24 p.m.

	While Ron Rackley's arguments as to what to tell an FCC agent
	concerning loading coils are reasonable and make sense from an
	engineering standpoint, what he doesn't realize is that when you
	are being inspected the last thing you want to do is to be coming
	off as a wiseass. Just ask the owner of the cluster who was
	recently busted (different issue but same idea). He now apparently
	has a reputation within FCC as being a scofflaw because he stood
	his ground, and no one will go to bat on his behalf because they
	don't want to risk any standing they might have with FCC (and also
	because based on this incident the legality of clustering appears
	to be less than airtight). Maybe Ron is well-connected with FCC
	officials and thus confident he could successfully argue his
	point, but I would wager most Part 15ers are not so lucky.

	While I don't recall where the loading coil interpretation I was
	referring to was posted (I thought maybe it was on Crash's site,
	or in the LWCA messageboard archives, but it was a while ago in
	any case so I thought everyone had seen it by now), here is an
	excerpt from a December 15, 1998 email to me from John Reed, a
	senior engineer at the OET Division of FCC responsible for Part 15
	rules:

	"Section 15.219 permits a transmitter in the AM broadcast band with
	an input (not output) power to the final RF stage of up to 100 mW
	provided the total length of the antenna plus connecting lead plus
	ground lead does not exceed 3 meters. Note that this 3 meters
	length is the electrical length. If a tuning coil is added, the
	electrical length (i.e., length of the coiled wiring) of that coil
	is included as part of this 3 meter length."

	He goes on to say, in another email, dated the same:

	"Under Section 15.219, the rules specify only the length of the
	connecting cable, antenna and ground lead. While several people
	argue that this should not include the windings in a loading coil,
	please note that the rule is based on 'length' not 'height.' This
	is done specifically to reduce antenna efficiency and
	corresponding transmission range."

	He also states later in this email that there is no range limit
	under Part 15. (Any limit would naturally be that imposed by
	complying with the rules).

	The official party line with respect to loading coils appears to
	be: don't make it physically part of the antenna unless you can
	keep the total length under the legal limit (that means using a
	ferrite core to get enough inductance if you do.) It may not seem
	to make much sense from Ron's engineering perspective, but the
	rules are the rules so it is best to do things the way they want
	them done especially when you're the "little guy" with no pull.
	That also means distributed loading (like helicals) is illegal if
	it can't meet this definition, as would anything else in the
	antenna that makes it over 3 meters in length if stretched out
	straight or otherwise measured in terms of total length. That is
	why I even adopt the "ultra-conservative" approach of considering
	the *diameter* of a tophat, not its radius, as many
	Lowfers/Medfers do, as the "length" factor to be added to the
	total.

	A loading coil at the base of the antenna, in the final or ATU
	enclosure, would seem not to be considered to be part of the
	antenna (and note that it is often called a "tuning coil" instead
	of "loading coil" although that is a taxonomic technicality).
	Obviously you have to have some sort of coil somewhere for the
	thing to work *at all*. The method that appears to have the FCC
	"Seal of Approval" is when the coil is inside the same box as the
	final (or ATU, if that config. is used) or even made part of the
	final tank itself; these arrangements apparently make it (from
	their standpoint) part of the transmitter (or ATU) and not part of
	the antenna. The best evidence of this is that all FCC Certified
	(Type Accepted) rigs do it this way, and all do have coils.

	I'm not trying to be a nitpicker here, and I'd be the last one to
	discourage experimentation with ways of increasing efficiency
	within the rules, but I don't want to see anyone get busted when
	they are otherwise making the effort to try to be legal by
	choosing to comply with Part 15 in the first place.

	I suppose to clarify I should not have implied that center loading
	per se is illegal, but rather it would be if the length of wire
	used to wind the coil exceeded the legal limit when added to the
	remainder of the antenna/feedline/groundlead length. The thing is,
	most people who use center loading coils in one form or another
	tend to go right away for the classic air core type which needs a
	lot of wire (way over the limit) for sufficient inductance,
	perhaps from ham radio practice. In homebrew Part 15 designs, you
	should be able to use an air core coil, but put it inside the
	transmitter or ATU box or otherwise integrate it into the final
	tank design.

	Jon

	remove "spammers.keep.out."

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

       Name: Crash Knorr
       E-Mail: [email protected]
       Date: 12/5/02 4:18 a.m.

	Jon, you make some good points but IMHO the true "ultra
	conservative" approach is to advise people to use an FCC certified
	transmitter + antenna combo. People who are super jittery about
	inspections should not be fooling around with homebrew anything.

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

       Name: Jonathan Smick
       E-Mail: [email protected]
       Date: 12/5/02 5:55 p.m.

	True, but those who want to operate bands like LF for which there
	are no Certified rigs available have no choice but to go the
	homebrew route. Also, Certification is no "magical protective
	shield" against enforcement action; again, just ask the guy with
	the (former) Hamilton cluster, or the owner of Village Radio with
	regard to his defunct FM outlet.

	While homebrew gear may in theory be subject to greater scrutiny
	at time of inspection compared with a Certified unit, ultimately
	whether your station survives the visit will be determined by how
	closely you followed the rules (or the most widely-accepted
	interpretation thereof). If a transmitter is operated out of
	compliance Certification won't save your butt.

	Jon

	remove "spam.arrest."

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