if anyone is interested ............

http://www.dx-antennas.com/Coax.htm

"WHAT LENGTH?
As mentioned the best length is the shortest, in this way the loss due to the cable is the lowest.
There can be one advantage by extending the length of the cable:.
A HALF WAVE coax cable or ANY multiple (1, 1½, 2 wavelength) length of this will show you: "exactly the same input resistance at both ends of cable". In normal words:
You can measure the exact SWR from the antenna with these lengths of coax cable.If your antenna is truly 1:1 it doesn't matter, each SWR measurement anywhere on the line and you will find 1:1.
Only when your SWR isn't 1:1 but higher your measurements will change according to length, this is when it can come in handy to keep the line a half wave long (or any multiple). "



"COAX AND VELOCITY FACTORThe shielding and the core of a coax form a capacitor. Through the use of insulation material, the value of the capacitor is bigger then it would be in air, and this has the effect of slowing down the signal. This can be of great importance in some applications, although for many purposes it does not needed this information ;-)Velocity factor
The speed at which the signal travels is normally given the abbreviation VF and this is the fraction of the speed at which the signal travels when compared to a signal traveling in free space. So VF for a signal traveling at the speed of light would be 1.0, and for one traveling at half the speed of light it would be 0.5.

The velocity factor of the coax cable is found by VF = 1 / SQRT (dielectric constant)Coax cable electrical length
One important factor of a coax cable in some applications is the wavelength of the signals traveling in it. In the same way that the wavelength of a signal is the speed of light divided by the frequency for free space, the same is also true in any other medium. As the speed of the wave has been reduced, so too is the wavelength reduced by the same factor. So if the velocity factor of the coax cable is 0,66, then the wavelength is 0,66 times the wavelength in free space.

In some instances lengths of coax cable are cut to a specific length to act as an impedance transformed or a resonant circuit, then this needs to be taken into consideration when determining the required length of coax cable.
The advantage of using a coax cable with a low velocity factor is that the length of coax cable required for the resonant length is shorter than if it had a figure approaching one. For example, 1/4 lambda 75ohm coax (VF * 1/4 lambda length) for transform the impedance from 125ohm to 50ohm. "