[Antennas] Buried radial question

Mon, 3 Mar 2003 17:38:46 -0600

Dennis, I recognize some of my own words there so let me frame a brief
answer.

The radials are in the near field of the antenna. Thus they have current
induced in them by the radiation from the "antenna" part of the system. that
current flows through space from the antenna to the radials and back to the
interior of the coax shield and back to the transmitter. Current leaves the
transmitter through the coax center conductor and flows to the antenna base.
The coax braid is connected to the radials and usually to earth ground as
well. The currents induced in the radials flow back to the coax braid and
complete the circuit back to the transmitter.

Now, why doesn't all this current cause radiation? It does, but if the
installation is designed right, not a great deal. First, the fields produced
by the radials tend to cancel one another due to the ideal symmetry of the
radial field. One radial will radiate very well. Two radials 180 deg apart
will tend to cancel one another since the current direction is opposite in
each of the pair. The more radials the more the fields tend to cancel one
another. This is true whether the radials are elevated, on the ground or
under the ground.

Radials on or under the ground surface will tend to be inefficient radiators
due to the losses induced by the proximity of the soil, etc.

So, the ideal symmetrical radial field is out there not to reflect anything,
although some reflection no doubt occurs, but rather to capture the
displacement current flowing from the antenna through space back to the coax
braid and back to the transmitter. Without the radials, the current would
have to travel through lossy soil and that reduces efficiency.

This is but a thumbnail sketch of the what is happening, so please consult
the ARRL Antenna Book, among others, for more detail and a better
explanation.

But, hope this bit helps . . .

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
Fairview, TX 30 mi NE of Dallas in Collin county EM13QE
"In the 57th year and it just keeps getting better!"

> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]]On Behalf Of k1drw
> Sent: Monday, March 03, 2003 5:14 PM
> To: [email protected]
> Subject: [Antennas] Buried radial question
>
>
> I was reading a reply to the question about buried radials -
> insulated -vs-
> non-insulated. Excerpt from the answer:  "The radials should present the
> lowest loss path possible in order to not degrade the efficiency of the
> antenna installation.  As to burial, the whole idea of a radial
> field is to
> capture displacement current being returned to the transmitter
> via the coax
> inner braid".
>
> I have learned much technical detail about this hobby in the
> couple of short
> years as a Ham but several fundamental concepts still escape me.
> I have just
> moved to another state and do not know any local Elmers yet.
>
> QUESTION:  I have an HF2V and use the radial kit supplied for
> this antenna -
> 12ea 32' insulated, slightly buried radials.  I still don't understand the
> concept applied here with the radials collecting and returning current.
> When I installed my HF2V, I thought the radials reflected RF like the main
> part of the antenna, just serving as the other half of a dipole.  If the
> radials just collect current and do not radiate, what happens to
> the current
> collected - what is its use...?
>   Dennis, k1drw