[Elecraft] BL-2 Connection To An Unbalanced Wire Antenna

[Ron D'Eau Claire]

Jim, IMX it's a mistake to equate "RF ground" with an Earth connection.

An RF "ground" is just a low-impedance, low-reactance current sink for RF.
Of course it is an integral part of the antenna circuit.

An RF "ground" would not be expected to radiate, and most "counterpoise" or
"radial" setups don't radiate a significant amount of energy*: 

1) Counterpoises near the Earth and on-ground "radials" tend to couple all
their energy into the lossy dielectric of the Earth, never to be seen again.
This is how BCB stations achieve a good RF ground generally using 120 0.2
wavelength radials around their towers to couple the RF into the Earth. 

2) Elevated radials will radiate a lot unless they are carefully balanced
and symmetrical so "legs" produce RF fields that cancel each other outside
of the immediate area of the antenna. Such radials, like any RF ground,
*are* part of the antenna circuit but, when properly designed, they are a
non-radiating "current sink". In the common "ground plane" designs, they
also decouple the radiating element from the feed line, providing an RF
"ground" not only for the radiator but also grounding the feed line at the
antenna so RF currents don't flow down the outside of the coax shield. 

Ron AC7AC

* Students have asked me what happens if they use only one radial with a 1/4
wave antenna. I reply that if they make it 1/4 wave long, then elevate them
both into the air and arrange them to run in opposite directions for maximum
efficiency, one 'radial' works just fine. If they draw out the antenna I
described on paper they'll recognize the common center fed dipole antenna.
In that case, there's no problem with the "radial" radiating.


-----Original Message-----

On Tue, 31 Mar 2009 18:43:39 -0700, Ron D'Eau Claire wrote:

>But it *IS* a ground for RF purposes

Nope! It has NO relationship with the earth, nor is one needed. This 
use of the word "ground" is an ongoing source of confusion and 
misunderstandings. Hams to go extremes to install ground rods, 
thinking that it will improve the performance of their antennas or 
make their radios quieter or fix RFI. A connection to earth does NOT 
do any of those things. It IS critical for lightning protection. 
That's all. 

Radials are not GROUND in any sense. They are part of the antenna! 
Indeed, their purpose is to intercept the fields produced by the 
antenna and by providing a low resistance path for return currents, 
prevent those fields from producing current in the lossy earth. 
There is an excellent discussion of this by Rudy Severns, N6LF, both 
in the ARRL Antenna Book and on his website. 

73,

Jim Brown K9YC