Galaxy DX88HL

http://www.k0bg.com/

Everything you ever needed to know about proper grounding can be found on this site. Follow his directions and it will make a HUGE difference

 

I have always believed that if you change coax length and s.w.r does not change then you have a perfect antenna match. Just my opinion.

 

How did that article calculate 18 feet?
SWR never changes with cable length but impedance will, which is why you need an antenna analyzer if you insist on using anything other than a half wavelength of cable.

 

If you don't see an swr change when impedence changes, what would this mean?

 

This means you're not looking directly at the feedpoint.
It also means you're looking at it with a piece of equipment a little bit more sophisticated than an SWR meter.
It also means that there is some reactance in the antenna itself.
Since changing cable length changes the impedance perceived by the SWR meter it will show changes in readings but those readings will not be accurate when compared to the feedpoint impedance which remains constant.
That's why an antenna analyzer should always be used since you cannot fool it into providing a false reading.

Think of a cable as a capacitor.
The center conductor and shield form a capacitor.
As the capacitor charges or discharges, a current flows through it which is restricted by the internal resistance of the capacitor. This internal resistance is commonly known as Capacitive Reactance and is given the symbol XC in Ohms.

Unlike resistance which has a fixed value, for example, 100Ωs, 1kΩ, 10kΩ etc, (this is because resistance obeys Ohms Law), Capacitive Reactance varies with the applied frequency so any variation in supply frequency will have a big effect on the capacitors, “capacitive reactance” value.

As the frequency applied to the capacitor increases, its effect is to decrease its reactance (measured in ohms). Likewise as the frequency across the capacitor decreases its reactance value increases. This variation is called the capacitors complex impedance.

Complex impedance exists because the electrons in the form of an electrical charge on the capacitor plates, pass from one plate to the other more rapidly with respect to the varying frequency.

As the frequency increases, the capacitor passes more charge across the plates in a given time resulting in a greater current flow through the capacitor appearing as if the internal resistance of the capacitor has decreased. Therefore, a capacitor connected to a circuit that changes over a given range of frequencies can be said to be “Frequency Dependant”.

 

That depends on what tool you are measuring with.

 

18 feet is a big fat myth. Length does matter, but it ain't 18' (in fact, it depends on the type of coax, velocity factor is part of the equation) and 3' increments are BS too.

 

For hams with antenna tuners it doesn't matter.