Hello to all,

We are in the process of designing the "Five sloping dipoles suspended from one support" for the ARRL's Antenna Book.

The text says that "The 36-foot length of feed line serves to increase the length of the element about 5%".

But suppose we want to increase the length by other factors (percentage), how to determine the (new) correct length?

A formula and/or a theoretical explanation would be much welcome..!

73 de Pierre VE2PID

Pierre

It's a bit of a hard antenna to get working in my experiance, however it can
be made to work. See link

http://vk6ysf.com/40m_sloper.htm

Regards

Peter

"ve2pid" wrote in message
...
Hello to all,

We are in the process of designing the "Five sloping dipoles suspended
from one support" for the ARRL's Antenna Book.

The text says that "The 36-foot length of feed line serves to increase the
length of the element about 5%".

But suppose we want to increase the length by other factors (percentage),
how to determine the (new) correct length?

A formula and/or a theoretical explanation would be much welcome..!

73 de Pierre VE2PID

On Monday, August 5, 2013 9:52:31 PM UTC-5, ve2pid wrote:
A formula and/or a theoretical explanation would be much welcome..!

I don't know exactly what you are asking for but a tuned feeder increases the electrical length of an antenna system because the forward wave and reflected wave have farther to travel, i.e. additional delays are introduced. A stub can accomplish the same function.

Here is an empirical chart that might help. Given the wavelength of a center-fed dipole, this chart indicates the wavelength of ladder-line needed to resonate the system. One can change wavelength to degrees if desired.

http://www.w5dxp.com/majic.gif

For instance, to bring a 0.4WL (144 degree) CF dipole to resonance, 0.12WL (43.2 degrees) of ladder-line is required. To bring a 0.8WL (288 degree) CF dipole to resonance, 0.3WL (108 degrees) of ladder-line is required. As you can see, it is not a linear relationship and resembles a tangent function..

That is a chart from my no-tuner all-HF-band antenna article:

http://www.w5dxp.com/notuner.htm
--
73, Cecil, w5dxp.com