Stub revisited
 

What is an example of using a stub on a ham antenna, its real purpose
and how it does it?

Like a R5 or beam.

On Mon, 03 Jan 2005 18:18:19 -0800, bbnn wrote:

What is an example of using a stub on a ham antenna, its real purpose
and how it does it?

Like a R5 or beam.

If you have access to the catalogs, antenna specs or even the
advertisements from HyGain, you can see stubs all over their
verticals.

As to its real purpose. It is often, but not exclusively a means of
imposing the equivalent of an open circuit in a part of the antenna,
so as to make the antenna seem shorter at that frequency.

In other applications a stub is just a way of inserting a capacitance
or an inductance into the feedline. The inductance or capacitance
obtained in this way is generally cheaper and less vulnerable to the
elements than using a discrete component.

As to how it does it - it is the nature of a section of transmission
line (stub) to transform any non-matching impedance at one end into a
different impedance seen looking into the other end. In the particular
case of a stub the terminating impedance is usually a short or an
open, thus reflecting a pure reactance to the other end. If you want
more detail than that, then it's time to start looking into an
understanding of the transmission line equations.


Bob, W9DMK, Dahlgren, VA
http://www.qsl.net/w9dmk

What is an example of using a stub on a ham antenna, its real purpose
and how it does it?

Hi, A stub used on a ham antenna is generally a "matching" stub. It is a
section of transmission line that exhibits capacitive or inductive reactance
depending on the length and termination of the line. (open or short). Used to
transform a complex antenna impedance to the feedline characteristic impedance.
It may or not require other devices to realize a successful impedance
transformation.
I don't know what an R5 is, on beams, a hairpin match (stub) is often used
for impedance matching.
73 Gary N4AST