[Lowfer] Active Whips

[ToddRoberts2001 at aol.com]

I do not completely agree that the coax running up to an
active whip is the same as a longer antenna as far as receiving quiet  
signals goes.
Using a 30 foot long coax up to an elevated active whip 3 feet long is  not
the same as a "33 foot long antenna".
 
Of course the ground return is part of an active whip antenna,
but there are other things going on when you raise a short active
whip high in the air versus a ground-mounted vertical or wire of the
same length as the active whip plus feedline.
 
When you raise an active whip high above ground into the clear  there  is 
less 
nearby ground clutter
such as trees, buildings and shrubs to attenuate the signal. That is 
only common sense.
The E-field is less attenuated high above ground. The Amrad article
in QST explains that trees and surroundings form an "electrostatic
blanket" below an average height above ground that will
attenuate E-field signals on LF and VLF.
 
Also I have confirmed a definite improvement in signal-to-noise
ratio using a short active whip mounted high above ground
versus a ground-mounted vertical element of the same height.
 
For example when receiving VLF Germany on 23.4kHz at a height of
5 feet the line noise level was reading an S-7 and Germany 23.4 was  
reading  an S-3.
By raising the  3 ft active whip to 30 feet above ground level the  
constant noise level
dropped to an S-3 while the signal on 23.4kHz increased to about an
S-8. This is a clear improvement in signal to noise ratio by raising a  
short
active whip antenna high above ground level. Something you cannot
do by running a longwire or vertical element of the same length from  the
ground up.
 
If this was the same as a 33 ft. ground-mounted vertical then the  noise
level would probably stay the same at S-7 or perhaps greater with a  longer
antenna element. Elevating a short active whip definitely improved  the
signal-to-noise ratio on VLF and helped to isolate the antenna from noise  
running 
along ground level. This is one advantage of an isolated short active  whip 
mounted
high and in the clear.
73 - Todd WD4NGG
 
 
 
In a message dated 1/24/2013 9:10:54 A.M. Eastern Standard Time,  
jrusgrove at comcast.net writes:
Good discussion.

Years back I decided to  investigate the much ballyhooed PA0RDT Mini Whip 
antenna with it's tiny  
antenna element. The test involved mounting it at ground level over a  
conductive screen ... along 
with several other 1M and longer e probe  antennas. Bet you can guess the 
results. Trying to point 
out that the  feedline of the elevated Mini Whip was actually part of the 
antenna was met with  great 
criticism ... so I finally gave up the 'crusade'. Folks *wanted* to  
believe in magic ... that the 
tiny antenna element was doing all the work  ... even though their own 
tests showed that it needed to 
be elevated several  meters to be effective.

I use an elevated e probe here for VLF and  general purpose LF/MF work with 
an elevated radial system 
directly under the  antenna ... along with feedline decoupling measures. 
This reduces the effect of  
the feedline to great measure but doesn't completely eliminate  it.

Jay W1VD  WD2XNS  WE2XGR/2