[TenTec] The Rogers /Dobbins ARL Folded Conical Helix Antenna paper now published. Revolution in small HF Antenna design!

[Tom Rauch]

> It can be further reduced in height over the example in the paper, and
> calculations show that it should be possible to operate on 160m with a
> patio fitting antenna with 90 per cent efficiency!  That was not a

That might indicate someone has a *very* large patio or a very poor 
calculator. 

> (with attendant losses), are needed.  You do have to use a transmatch
> to move around the band.

Bandwidth is tied to energy storage in the system. When an 
antenna is physically small and efficient, energy storage is very 
high and bandwidth will be very small compared to larger similar 
styles of antenna. Unless there is some form of tuning adjustment, 
bandwidth would be a few kilohertz or less even with efficiencies of 
only a few percent in a 20-foot-long 160-meter antenna.

If you are seeing wide bandwidths, low currents, and low voltages 
that is a big warning flag that efficiency is also low.

> Materials to make the elements include two differing diameters of
> wire; even RG 58 has been used for one element that is coiled into the
> funnel.  The folding of the element overcomes the fact that an
> electrically small cone would have an input resistance much less than
> 50 ohms at first resonance. Folding raises this back to 50 ohms.  The
> fold is a shorted transmission line.  This antenna was produced
> without dielectric loading.  However, that is another method of
> altering the resonance.

Radiation occurs from charge acceleration. This all boils down to 
the ampere-feet of **linear spatial distance** carrying in-phase 
currents. As the total *linear spatial distance* decreases, current 
must proportionally increase for the same power radiated. 

In other words, if a dipole antenna is ten feet from tip-to-tip, that is 
the maximum possible linear spatial distance we can accelerate 
charges through. We can fold, bend, or spiral until the cows come 
home (or until we have a thousand feet of wire packed in a ten foot 
area).and we still have a ten-foot dipole antenna. 

That is why current in ALL small efficient antennas increases a 
great deal. As a matter of fact, with small antennas we must 
double current as we halve the length to radiate the same power. 
That means radiation resistance (which is NOT the resistance at 
the feedpoint) must decrease by a factor of four. It's I squared R 
and will be forever. 

For a given applied power we either must double currents causing 
radiation every time the physical area is halved or we have very 
high loss. With that increased current, comes increased conductor 
losses.   
 
> Attempts to calculate the SWR and input impedance with NEC 4 did not
> give consistent results. 

That might be worth looking into. It generally means all the 
information was not entered correctly.

> The pattern of this antenna is much like that of a vertical (elemental
> monopole), that is ground mounted. The vertically polarized power
> level was 22 dB above the horizontally polarized component.  The
> antenna gain is 4.7 dBi, (over isotropic).

How was that measured?

If the pattern is vertically polarized and the antenna is near earth, 
how can system efficiency be 90% without a large groundplane 
even if the radiator itself is lossless?
73, Tom W8JI
W8JI@contesting.com