[Lowfer] Ultimate LOWFER Transmitter?

[Stewart Nelson]

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


> > > This is the principle behind multiple tuned vertical radiator systems of
> > the
> > > type used at VLF stations such as SAQ, for example.
> 
> If you'll look at a typical schematic you'll see that the arrangement
> really involves using a number of ground circuits in parallel, reducing
> the ground losses.
> 
> > I am not sure if I am being subject to a gigantic leg-pull but here goes.
> > 
> > So you are saying that if I start with a typical LF antenna with say 1%
> > efficiency and feed it with say 1 watt (10mW radiated).
> 
> For a 50 foot top loaded tower to get even 1% efficiency would require
> a ground resistance of around three ohms and no other circuit losses. 
> That would really be a miracle for a typical lowerfer installation, but
> think a few guys are just about doing it.
> 
> 
> 
> > I would be interested in a rigorous explanation (no resistors and batteries
> > please :-) which further details the claimed doubling of efficiency for
> > doubling of independant radiators.    Of course we are not talking about
> > arrays of such a size as to have a directional effect.
> > 
> > 73s Steve Olney VK2ZTO
> 
> Even small arrays can have some directional properties, and some
> receiving sites use arrays of spaced loops to minimize interference.  Of
> course, there is no gain.
> 
> Ed