[Lowfer] Lo-Medfer Loading Coil

[Bill Ashlock]

Warren,

 

The actual value depends on the diameter of the conductor and to some extent the height above ground. We are probably both right on the value for capacity/meter and your 6pf is probably the correct value for a thin conductor such as a wire. The capacity varies to the log of the diameter so the capacity increases rather slowly with incremental increases in diameter. I'll see if I can find the text book that has this equation, where it is actually derived from electric field theory. 

 

I think what is really interesting (and not much is made of this in normal text books) is that the inductance of a straight conductor varies in a similar fashion and a point of resonance occurs when the inductive reactance of the conductor is equal to the capacitive reactance. That occurs when the length of the rod is approx 1/4 WL.

 

73

Bill

 

PS: Relative to your final goal: Watch out for that "hot" chassis effect :) Might even pose a real problem for modern auto electronics.
 
> Date: Wed, 8 Apr 2009 19:00:22 -0300
> From: wd2xgj at gmail.com
> To: lowfer at mailman.qth.net
> Subject: Re: [Lowfer] Lo-Medfer Loading Coil
> 
> Hi Bill,
> 
> Thanks, but according to the references I've seen, its 6pF/m
> rather than 8pF/m.
> Yes, its for portable/mobile operation on 500.
> 
> 
> 
> On 4/8/09, Bill Ashlock <ashlockw at hotmail.com> wrote:
> >
> > Warren,
> >
> >
> >
> > What's wrong with doing this the old fashioned way? Assume C = approx 8pf
> > per meter of antenna length and solve for the inductance (L) to resonate
> > 500KHz using 2pi*f = 1/sq rt (L*C). Comes out a little under 3.5mH. QED!
> >
> >
> >
> > BTW is this for a mobile rig? As in "break, break, old buddy" :)
> >
> >
> >
> > Bill
> >
> >> Date: Tue, 7 Apr 2009 11:08:37 -0300
> >> From: wd2xgj at gmail.com
> >> To: lowfer at mailman.qth.net
> >> Subject: [Lowfer] Lo-Medfer Loading Coil
> >>
> >> Hello the list,
> >>
> >> I am considering building a very small 500kHz vertical antenna (4
> >> meters) with a loading coil at the base. Modeling the antenna with
> >> EZNEC I get value of just under 3.5 millihenries for the loading coil.
> >> Has anyone built a Medfer beacon for the low end of the band and can
> >> verify this number?
> >> Thanks,
> >>
> >> 73 Warren K2ORS
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> 
> -- 
> 73 Warren K2ORS
> WD2XGJ
> WD2XSH/23
> WE2XEB/2
> WE2XGR/1
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