[Moon-net] cable losses ?

[Leif Asbrink]

Hi Jurgen,

> We nearly have the same setup; FPQ: 4x 9elxpol in +config , LWT 4x9el in X
> config
> FPQ is having a 4-port divider in the centre of the frame and uses 4x 5m
> length as phase line total use of cable =20m
The loss is then the nominal loss of 5 meters of cable: (=5*nom)
(Each cable carries 25% of the power and attenuates its own power only.)

> LWT is having coax dividers and is combining the 2 left antennas with a T
> junction,the 2 right antennas with a T junction  these 2 t junctions are
> connected together with n(odd)* 1/4λ lines tog et 50ohm again. Total use of
> cable  = 15m ( in fact this way the 4 port divider of coax is having longer
> legs)
The exact lengths matter. There would be four cables of length X and two
cables of n(odd)/4 wl. All I know is 4*X+n/2λ = 15m so I can not figure out
what X is without knowing the wave speed.

Here the loss would be (X + F*n/4λ)*nom 
The factor F, the extra loss because SWR = 2 in the cable can be found
in ARRL handbook for example. In the current context we can assume that
losses are small and then F=1.25 

> For both systems we have run from each antenna the same length of cable to
> the preamp. But the total amount of cable in the system is 5M less in LWT
> system. So our simple way of thinking will say LESS cable is LESS losses. Is
> this true ?? 
NO. It is the other way around. 

anyway it's cheaper :-)
And the difference is small:-)

73

Leif / SM5BSZ