[Lowfer] New vertical Y antenna

[Bill Ashlock]

Warren,

The formula is: C = Eo[(pi r^2/d) + r ln(16pi r/d-1)]

Where: C = capacity between circular planes; Eo = 8.85 pf ; pi = 3.14; r = radius of circular planes in meters; d = distance between planes in meters; ln = natural logarithm

Note that the first part of the formula represents the capacity between planes if spacing is very small, and is given in most electric fields text books, namely:   C = Eo A/d   Note, also, that the capacity result depends on the AREA of the planes. You will find that the second term, mainly accounting for the fringe field, amounts to about double the capacity value of the first term, but depends on the RADIUS of the planes, not the area. This seems to make sense because the fringe exists around the perimeter of the planes and it's length is proportional to the radius.

I think this WOULD make for a pretty hot 500K antenna! That will be on my list of tests.

Bill

> From: k2ors at verizon.net
> To: lowfer at mailman.qth.net
> Date: Tue, 13 Dec 2011 20:44:15 -0500
> Subject: Re: [Lowfer] New vertical Y antenna
> 
> Bill,
>    Yes please post details.
> How about loading it up on 500kHz ?
> 
> 73 K2ORS
> 
> 
> ----- Original Message ----- 
> From: "Bill Ashlock" <ashlockw at hotmail.com>
> To: <lowfer at mailman.qth.net>
> Sent: Tuesday, December 13, 2011 8:36 PM
> Subject: [Lowfer] New vertical Y antenna
> 
> 
> >
> > Rick and others,
> >
> > I'm all set to begin on-air testing of this new antenna once I install the 
> > loading coil and transmitter at the base and run wires to it. The capacity 
> > measurements between upper and lower "Ys" (plus fill-in wires) are 
> > complete and I'm seeing approx 400pf between them. This makes for a low 
> > Rac in the loading coil because of the relatively low inductance of 185mh 
> > at 185.3KHz.
> >
> > Turned out there was quite a large-sized finge field from the top "Y" and 
> > I had to expand the lower "Y" in order to capture a good percentage of it. 
> > That rule of thumb saying the radius of the ground radials must be at 
> > least equal to the height of the antenna proved to be true, BUT I think 
> > this applies to a vertical WITHOUT top hat. When a top hat is used it 
> > appears the radius must be equal to the antenna height PLUS the radius of 
> > the top hat. At any rate it will be interesting to see how the total Rac 
> > for this antenna comes out when I apply power, but I suspect it will be 
> > very low if I have captured as much of the fringe field as capacity 
> > measurements indicate. BTW there's a formula I found for the capacity 
> > between two circular conductive planes separated by a large distance (like 
> > 50ft) that seems to work. For Lowfer antennas it comes out approx 3 times 
> > the capacity derived from the formula that is typically given in text 
> > books for closely spaced planes not accounting for th
> > e fringe field off to the side. It's a bit lengthy but if anyone is 
> > interested, I'll post it.
> >
> > Bill
> >
> >
> >
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