[Lowfer] Ultimate LOWFER Transmitter?

[Ed Phillips]

Stewart Nelson wrote:
> 
> Hi Steve and all,
> 
> Assume that the "base" lowfer antenna has an 0.02 ohm radiation resistance,
> a 20 ohm loss resistance (ground + coil loss), and is tuned to be a
> 20 ohm resistive load at the operating frequency.
> 
> Now, we build a second antenna, identical to the first, about 100 feet away.
> Take two 50-foot lengths of 20-ohm coax, and connect the antenna systems
> "in parallel", with feed at the midpoint.  I contend that the impedance
> seen at the new feed will be only slightly greater than 10 ohms, but that
> the radiation resistance of the combination will still be 20 milliohms.
> As a result, the combined system has almost 3 dB higher gain (less loss)
> than a single antenna.  (Of course, this combined system would not be
> a legal lowfer antenna, which is one reason for using multiple transmitters.)
> 
> If you disagree, do you believe that the radiation resistance of the
> combined system is lower?  Or that the impedance seen at the new feed
> will be much higher than 10 ohms?  Why?  I'll try to give a more
> rigorous explanation of that aspect.
> 
> 73,
> 
> Stewart KK7KA

	Last night I spend a couple of hours looking through the stuff on
antennas in Watt's "VLF Radio Engineering".  Endless detail on how to
calculate losses of all sorts.  It would appear that several VLF (~20
kHz in this case) antennas were built using a number of vertical
elements with bases driven in parallel, exactly what you describe.  Some
used individual top-loading umbrellas and some used a giant one covering
the whole array of vertical elements.  By far the most efficient antenna
ever built (the german "GIGANTE") used this configuration.  It was built
in late 1941 using galvanized steel conductors because of the shortage
of copper, and gave an overall efficiency as high as 60%.  Watt gives
measured data on a lot of the early antenna systems and efficiencies
ranged from about 10% to bit over 20%.  Typical radiation resistance was
of the order of 0.05 ohm, ground resistance of the order of 0.3 ohm, and
capacitance of the order of 0.05 to 0.1 ufd.  Those were enormous ground
systems and far beyond anything one could put up in his back yard or in
his neighbor's field.

	Anyone who can get access to a copy of Watt (its long out of print and
hard to find with the used book sellers) should do so.  He gives an
enormous amount of information of use to lowfers, and has a lot of stuff
on propagation which makes interesting reading in the light of the
recent success some guys have had.

Ed